Return to White Hound fan-fiction
Contact:
But Snape is just nasty, right? (post-DH version) a consideration of the evidence for Our Hero being exceptionally unpleasant
We know now that Snape is definitely one of the Good Guys, but this essay looks at the evidence that he is nevertheless a markedly unpleasant person, as often portrayed in fanon where the expression "IC (In-Character) Snape" means a Snape who is cold, spiteful, emotionless, domineering and cruel. Because Potter fandom is so vast, for anybody who reads fanfics on a regular basis the sheer volume of fannish stories can outweigh the original books, until it becomes difficult to keep track of what is canon and what fanon.
Even for those who love Snape there are many negative assumptions about his character and behaviour which tend to be taken as a "given". Some are undoubtedly true - there's no doubt that he has a difficult, jagged personality, an overbearing classroom manner and a malicious sense of humour - but many are derived from fanon and are only weakly supported by the books. That's not to say that it's impossible that e.g. teenage Severus was a serious racist, or that the Death Eaters were wholesale, random killers, and in some ways these things may make for a more interesting narrative. But there's a difference between ideas which can be got to fit in with canon and ideas which are strongly established in canon, and my interest is in teasing out that difference and showing that many of the negative assumptions about Snape's behaviour are just that - assumptions.
Many fen who dislike Snape argue that it's clear that JK Rowling intends him to be dislikeable, and that therefore where his actions are open to interpretation they should be interpreted negatively: but with Rowling authorial intent is a complex issue. There are places where you can say "She must have had a reason to include this detail" and make a stab at what that reason was. There are places where you can certainly say "She is deliberately creating such and such an impression" - but you also have to bear in mind that often, she sets out deliberately to create an impression which is actually false, and not only as regards Snape and Dumbledore. There was the story of Winky and the Crouches, for example, where it looks as if Barty Snr is treating his house-elf as a pathetic slave and punishing her disobedience, and you have to be paying very close attention to realise that he had allowed Winky to make major decisions for the household and to persuade him to act against his better judgement, and she had then chickened out of an arrangement which she herself had insisted on, with disastrous consequences. Or the "little" matter of Grawp, where Rowling sets up a portentuous warning from the centaurs which sounds like The Voice of the Author, telling us that Hagrid's attempt to civilise Grawp is doomed - and then the centaurs turn out to be flat wrong. So whilst there are places where we can say yes, Rowling apparently intends Snape to e.g. come across as biased here, we cannot say with certainty that she intends him to be biased.
The essay as it was first draughted was substantially updated in June 2009 to take account of topics raised on the Loose Canon discussion group, and many of the points raised were contributed by members of that group or by other Snape fen including wynnleaf, duj, Dyce, Verity Brown, Red Hen, excessivelyperky, cinnamon_luvr, sionna_raven and Mary Johnson.
Page references for quotes refer to the UK hardback editions. A few lengthy digressions on topics such as the date when the Potters went into hiding, and the nature of Sectumsempra and of curses generally, have been hived off into separate mini-essays to prevent them from distracting attention from the main thrust of this one.
N.B.: This essay has been somewhat re-worked in the light of new evidence presented in Deathly Hallows, but the original, pre-DH version can still be viewed here for comparison purposes, so you can see what I did and didn't get right.
contents list
One of the things we think we know about Snape as a schoolboy is that he was already a Dark wizard in the making, but within the books this rests solely on statements by Sirius, who hated him. Nor is there just an absence of evidence that he was very heavily into the Dark Arts at school: there is an actual presence of evidence that he wasn't, or at least that he wasn't generally considered to be. In some ways this is a pity, because the idea of Severus as a budding Dark magician is kind-of cool, dramatically speaking; but canon doesn't really support it.
JK Rowling did say in a Live Chat that young Snape loved Dark Magic and was "drawn to ... loathesome people and acts", and that this was a factor in Lily's failure to develop romantic feelings for him; but she didn't say whether he actually performed any loathesome acts himself and we see in the books that as at a point partway through fifth year, just after Severus was nearly fed to a werewolf, Lily accuses him of hanging around with somebody who does Dark Magic, but not of doing it himself - which suggests that if he did take up Dark Magic himself it was after this scene, and after his life was threatened. By the end of the school year Lily would have broken up with him, so there really isn't much of a window for her to have decided she was rejecting his suit owing to his newly discovered interest in Dark Magic - unless "drawn to ... loathesome people and acts" just means "was friends with Avery and Mulciber".
Nor does Sirius or anyone in the books accuse Severus of involvement in Dark magic, but only in the Dark Arts. The whole issue is less clearcut than it appears. The accompanying essay on Sectumsempra and the nature of curses looks at, among other things, what Dark magic actually is, which is never established in the books. We can say with confidence that it does not equate directly to "magic which is self-evidently evil", because we are told that Beedle the Bard - and by implication Dumbledore, who is said to have held similar views to Beedle - merely "mistrusted" Dark magic. Most obviously evil magic seems to be classed as Dark, but by no means all magic classed as Dark is obviously evil. On the whole, "Dark" when applied to magic seems to mean "transgressive" - which can mean anything from powerful spells which are blatantly evil or which break the fundamental laws of magic, down to minor artefacts or potions which contravene some arbitrary Ministry restriction - and the Dark Arts are some sort of mildly illegal wizarding technology which includes some of the things Hagrid uses.
Keeping giant spiders, for example, seems to be a Dark Art, since Harry sees them being sold in Knockturn Alley, and we are told that everything he can see on sale there is a Dark Arts item. Just like Hagrid and his pet Acromantula, a teenager who took an interest in Dark Arts might do so because he had a very high opinion of his own ability to control a dangerous force, rather than because he intended to do harm.
Within the books, then, the information that young!Snape was fascinated by the Dark Arts comes only from Sirius, and he does say Dark Arts, not Dark magic. Lily, even when she is furious with Sev, does not accuse him of practising Dark magic himself: only of associating with other Slytherins who do - and this is in fifth year, when if Sirius is to be believed Snape already had an established reputation as a Dark wizard in the making.
Sirius does seem reasonably honest, and he does say it twice (once in the cave scene in GoF, once when he and Remus are reassuring Harry about the bullying which he saw in the Pensieve), which gives it slightly more weight. We can take it that he believes what he is saying. But although Sirius is honest it's clear he isn't always right. He must know Dumbledore well, since they were in the Order of the Phoenix together, yet in the same cave scene he says Dumbledore would never have hired Snape if Snape had ever worked for Voldemort, which we know isn't correct.
Sirius can't speak about Snape without being gratuitously insulting ("Slimy, oily, greasy-haired kid"; "little oddball" etc.). True, Remus does not contradict Sirius when he says that Snape was "up to his eyes" in the Dark Arts, but we've seen that Remus will suppress vital facts in order not to cause a scene, and that he was prepared to go along with Sirius's boyhood bullying of Snape. Once Sirius is no longer there to sway him, Remus tells Harry that both James and Sirius had "an old prejudice" against Snape. JK Rowling herself has said on her website that "Sirius claims that nobody is wholly good or wholly evil, and yet the way he acts towards Snape suggests that he cannot conceive of any latent good qualities there." So, we know without doubt that Sirius's own author intends him to be a biased source.
Nevertheless, Sirius is so honest that even when he is trying to rubbish Snape, he admits that he (an Order member, but one who was arrested before Snape's past was investigated by the Wizengamot) is not aware of any accusation that Snape was a Death Eater. Since he is trying to rubbish him, we can assume he means no rumour, not just no formal accusation, because if there had been a rumour you'd expect him to say so. And if Snape really had had a reputation of being deeply involved in Dark magic, I would have expected there to be a rumour that he was a Death Eater, even if he hadn't been.
Sirius says that "Snape knew more curses when he arrived at school than half the kids in seventh year". This is a profoundly traumatized man in his mid thirties, trying to remember an impression gained when he was eleven about somebody he is deeply prejudiced against. Nevertheless, let's assume it's true and see what it tells us.
The logical corollary is that Snape knew fewer curses than half the seventh years, or the same number. So Snape is being accused of precocity rather than monstrousness. And we know he was precocious, because he invented Levicorpus in the margin of a sixth-form text-book, and yet Remus tells us that Levicorpus enjoyed a vogue at Hogwarts for some months during their fifth year. Ergo, Snape was using a sixth year text as a note-book quite early in fifth year.
[We can assume Advanced Potion-Making was a NEWT text when Snape was at school, because even Umbridge admits that the fifth-year Potions class he later teaches is quite far ahead for their age, yet when they start Advanced Potion-Making in sixth year the recipes in it are new to them. Ergo, Advanced Potion-Making really is quite advanced.]
Knowing a lot of curses does suggest a penchant for combat spells, but several curses are either on the Hogwarts curriculum or readily available in the library. When Draco uses Locomotor mortis on Neville in first year he announces that he's been looking for somebody to practice it on and the Trio all recognise it at once, which suggests that they've been taught it, or at least taught about it, in class. Hermione already knows Petrificus totalus in first year, which she presumably got from a book, and in fourth year they learn Reductor from a book with McGonagall's blessing, and are taught about the Unforgivables. A student it seems may know several curses and yet not know anything which the school deems unacceptable. And how many curses is more curses than are known to half the new seventh years?
At the end of sixth year, Harry - who is such a Defence Against the Dark Arts expert that he's competent to teach it - knows Reductor, Locomotor mortis, Petrificus totalus and Furnunculus. He knows of the three Unforgivables but can't yet cast them effectively. And he knows Sectumsempra, which is also considered a curse.
[Harry also knows Impedimenta, but only once, in the US edition of GoF, is it called the Impediment Curse, and this seems to be an error. Everywhere else - including the same place in the UK edition - it's called the Impediment Jinx.]
So that's five curses he can perform, and three he knows of but can't really perform, most of them sanctioned by the school, for an Outstanding DADA student at the transition-point between sixth and seventh years. On this evidence, "knows more curses than half the seventh years" probably means "knows six curses". Indeed, we can assume fairly confidently that Severus didn't know any more than six or seven curses, because if even the most Outstanding DADA student starts seventh year knowing only eight curses, three of which he can't yet do, that means that if Severus had known more than six or seven he would have known more than almost all the seventh years, not just half of them, and Sirius would have said so.
Nor, of course, do we know whether he used those curses offensively, defensively or in a duelling club.
We also have to consider that the Marauders repeatedly hexed Snape, even by their own admission, and seem generally to have come out on top in their encounters (if they'd lost, Snape wouldn't have been so bitter about it, and James would have been able to produce a better excuse for attacking him than "he exists"). Evidently, they knew a lot of aggressive spells from an early age, too.
I suppose some people might interpret the scene in Deathly Hallows where a branch falls on young Petunia after she has mocked Snape as being proof that he was using curses even before he started at Hogwarts. But so far as I can see this scene is analogous to the ones where Harry unwittingly vanished the glass barrier at the zoo, or inflated his horrible aunt: a sudden involuntary, unconscious lash of wandless magic from a child who was angry and humiliated.
He may well have been taught hexes as quite a small child, though: whether or not he ever used them. Severus was born in 1960, in what looks as though it is probably the Manchester area. Out here in the real/Muggle world, from 1963 to 1965 that area was haunted by the paedophile serial killers known as the Moors Murderers, so Eileen Snape would have good reason to think that the Muggle world was dangerous and her son should be taught to defend himself.
What contemporary evidence is there that Snape was a Dark wizard? Lily accuses fifth-year Severus of associating with someone (Mulciber) who uses Dark magic, but not of using it himself. Nor does she accuse him of being involved in whatever Mulciber tried to do to Mary Macdonald, or even of witnessing it: she asks him if he knows about it, and since she will later say that her friends have been advising her to drop Severus, if he'd been present they would have made sure to tell her. Severus replies that whatever Mulciber did was just "a laugh", but since Lily says that Mulciber "tried" to perform Dark magic - that is, he didn't succeed in doing it - we don't know whether Severus means that Mulciber was trying to perform Dark magic which was meant to be amusing, or that Mulciber was joking and only pretending he was going to use Dark magic.
Assuming that Mulciber did try to perform a Dark spell (or use a Dark potion), we don't know if it was really bad or not. As an adult Death Eater Mulciber (a Mulciber, anyway) was famous for his use of Imperius, so it may be that he tried to Imperio Mary Macdonald - in which case, it was highly illegal, but how nasty he was being, and how appropriate or otherwise it was for Severus to play it down, depends on what he was trying to make her do - on which we have no information. It could be anything from magically-assisted rape to making her quack like a duck.
Nor do we know what the circumstances were. Mulciber could have been a bully singling out a victim for persecution, or a prankster like the Twins who scattered his hexes broadcast. He could have been a victim of bullying or other attack, defending himself against an aggressor. It could have happened in DADA class, or in a duelling club. In fact, given how inept teenage boys are at expressing sexual interest, it's entirely possible that Mulciber tried to provoke Mary because he fancied her. A friend of mine was mad keen on a girl at his school when he was about fifteen, and the only way he could think of to express his interest and admiration was to flick little pellets of rolled-up paper at her.
At any rate, probably all Severus knows about it is what Mulciber has told him, which will have presented Mulciber in the best possible light; and since, as we see, Severus has a great capacity for devotion to his friends, he will tend to believe him. In fact, Severus contrasts with Lily in this scene. Severus believes that whatever Mulciber did must have been OK because Mulciber said it was and Mulciber is his friend. Lily refuses to believe Severus's version of the werewolf incident, or even to discuss it properly, even though he's an old, close friend and even though what he's telling her is true. Severus's gullibility and willingness to make excuses for his friend Mulciber may be misguided, but it's more amiable than Lily's certainly misguided scepticism.
And whatever Mulciber did, it probably wasn't as bad as trying to feed somebody to a werewolf. Admittedly Lily doesn't know at that point quite how deadly what Sirius did was, but she won't allow Severus to tell her. And he, at least, knows that she is blaming him for hanging around with somebody who [perhaps] tried to pull a nasty prank, while she herself is associating with a would-be murderer. This presumably contributed to his tendency to play down whatever Mulciber did - and it's natural that he turns the subject away from Mulciber and onto the Marauders. Lily is complaining about something nasty done by one of Severus's housemates, which he evidently believes was intended as a joke (in one sense or another), so it's natural that his mind will turn towards the fact that only a couple of days ago, some Gryffindors tried to feed him to a werewolf as a joke - only he can't actually put it that way, because he's promised Dumbledore he won't tell.
Young!Snape writes long answers for his DADA OWL, suggesting his interest may be as much defensive as offensive. When Lily demands James tell her why he persecutes Snape, at which point coming up with a good answer would be strongly to James's advantage, James does not think to say "because he's a Dark wizard", which suggests that his evil reputation was not nearly as established as Sirius would later claim.
Of course, he may have developed a deep interest in the Dark Arts later, in sixth or seventh year. He had seen, after all, that the "Light" side were able to get away with attempted murder, and that James thought it acceptable to continue to attack him even after being promoted to Head Boy, so he would not see (it seems from his comments to Lily that he did not see) that practising Dark Arts was an obviously more evil thing to do than bullying people or trying to feed them to a werewolf. But we can certainly dismiss Sirius's claim that James persecuted Snape because he was famous for being heavily into Dark Arts, since we see James treating him with great cruelty in fifth year, at which point he clearly isn't regarded as a famously Dark wizard.
Sirius is not so far as we know a liar, so if he says James attacked Severus because Severus was into Dark Arts, that's probably what James told him - but James was a liar. We know this because he concealed his continued seventh year hex-war with Severus from Lily, knowing that it was something she would want to know about and would be angry about.
In fact, we see James begin to bully Severus on the train on their first day at Hogwarts, for no reason except that he wants to be in Slytherin and has a friend who is a girl, and Rowling has said at interview that James's bullying of Severus was at least partly caused by his, James's sexual jealousy of Severus's friendship with Lily. So Sirius's statement that James attacked Severus because he thought he was a Dark wizard is either a lie, by Sirius to Harry or by James to Sirius (because James attacked Severus when he knew nothing about him except that he wanted to be in Slytherin) or, if true, it means that James simply assumed without evidence that anybody who was in Slytherin was a Dark wizard (because he attacked Severus when he knew nothing about him except that he wanted to be in Slytherin). Sirius, coming from an apparently Dark family who were all Slytherins, may well sincerely believe the latter; but either way, it cannot be taken as strong evidence that Severus actually was Dark.
Then there is the issue of Sectumsempra. We do not know whether young!Snape invented it or merely learned it, but he certainly used it. How unpleasant a spell is it?
Sectumsempra means something like "cut every time" - so Snape may have either invented or learned it because it could be read as "Sever(us) forever". It's his signature-spell, literally, and as such goes with the "Half-Blood Prince" tag: half genuine boast, half clever pun.
We don't know if Severus invented the spell himself or not, although Harry assumes he merely copied it and that may be Rowling's intention. The punning name and the fact that at the end of HBP he accuses Harry of stealing his own spells, plural, when Harry has just tried to use Sectumsempra and Levicorpus, suggest that he did. The fact that the spell was just written in his book without any workings-out, and the fact that Remus speaks of it familiarly as if it is a known spell, suggest that he did not: and it's possible that he learned it because of its already-appropriate name, rather than giving it that name, and that by telling Harry not to use "my spells" he is issuing a general warning rather than actually counting how many of his spells Harry has already used.
The separate essay Sectumsempra and the nature of curses looks at what we can derive from canon about the nature of Sectumsempra, and of curses in the Potterverse generally. Basically the canon evidence shows that Sectumsempra is indeed a curse, but that "curse" does not equate to "obviously evil spell", but rather to something like "strong, potentially dangerous spell". Some curses are actually taught on the Hogwarts curriculum. They occupy the same sort of position as knives and gunpowder do in the Muggle world - things which can be used as weapons, or as useful tools for tasks like quarrying and carving.
Canon strongly suggests that all curses which are capable of amputating a body part (whether deliberately or by accident) result in a permanent amputation: the affected body-part cannot be regrown. In addition, curses which are classified as "Dark" create wounds which resist healing and scar very badly, similar to the persistent wounds which Bill Weasley received from the Dark creature Greyback. If Sectumsempra causes an amputation, the affected part cannot be regrown (George's ear) but the open wounds it leaves can be closed easily (George's ear again), and even very severe gashes caused by Sectumsempra heal without scarring if treated promptly (Draco's injuries in the bathroom scene). Therefore, Sectumsempra is a curse, but not a Dark curse.
The name "sever forever" sounds superficially as if it is a curse which was designed specifically to cause permanent amputation but this cannot be the case, unless it is a very, very old spell - so old that it predates all other spells which do the same. From what we are told, all curses which can cause amputation, cause permanent amputation, and Sectumsempra can hardly be the first cutting curse ever devised, unless it is ancient. Therefore, causing permanent amputation is not something for which a curse would need to be specifically designed, nor is it an effect noteworthy enough in itself to be a spell's name.
If Severus did invent the spell himself, he might have given it that name purely as a joke: but if it's analogous to the Half-Blood Prince tag it ought to have a literal meaning as well as a punning one. I would suggest that "cuts every time" means "the knife that never needs sharpening" - especially as Staysharp is a famous British brand of kitchen knife, and JKR is fond of names which are puns on British products (Spell-o-tape, Ethelred the Ever-Ready etc.).
We know from its effects on Draco, and on the Inferi in the cave - where Harry slashes at his opponents with all his considerable might, and yet doesn't actually cut them in half or chop any bits off them even though in the case of the Inferi he is trying to - that Sectumsempra equates to a knife rather than a sword, albeit a knife which can be projected at a distance. The fact that it cuts fairly shallowly, even when swung with full force, suggests that, far from being designed to cause amputation, it's been designed not to, as far as that's possible for a cutting curse. That is, the shallow nature of the wounds may be a safety-feature, to prevent it from cutting bone, or it may simply be rigged not to do so. Otherwise, it's hard to explain how Harry managed to hack away at the Inferi as hard as he could, and yet inflict only flesh wounds.
Severus's use of it against James during the underpants incident, whilst perhaps a little over the top given that James wasn't attempting to injure him physically at that point, is understandable when you consider that James was part of a gang who had previously put him in extreme danger of his life, either deliberately or recklessly. And his use of the spell was very controlled - he only gave James a little flick with it, and we know that that was all he intended to do, because we're told that he pointed his wand straight at James; and also because James was in between Severus and Lily. We see from the incident of George's ear that if Sectumsempra misses its intended target it keeps going until it hits something else, like a bullet, so if Severus had taken a wild swing at James he would have endangered Lily.
We do not know exactly when Severus learned or invented Sectumsempra. It's written in a sixth-year textbook which we know he was using as a notebook in fifth year or earlier (because he worked Levicorpus out in the margins of it, and that spell enjoyed a vogue during fifth year). If he invented it, then the lack of workings-out surrounding it may mean he had come up with it before he started using that book, and copied it across - but you would think in that case that he would simply remember it. The encyclopaedic knowledge of potions which he demonstrates in class suggests that he has a phenomenal memory. So it is likely that he copied it from elsewhere, or invented it on the spot, at the point at which he wrote it down.
There are a number of imponderables - for example we don't know when he started to use Advanced Potion-Making. He could have been so precocious he was using it in first year, but as it's a sixth-form text it's more likely he was using it in fourth and fifth years. We don't know whether he intended Sectumsempra, a knife-spell, as a weapon from the first, or whether he initially used it as a tool, for chopping potion ingredients without bruising them or for sneakily snipping shoelaces, and only later designated it "for enemies".
But whether he knew it beforehand or not, there is at least a very strong possibility that he only designated Sectumsempra "for enemies" some time in fifth year, after Sirius tried to feed him to a werewolf. After, that is, he knew that his "enemies" might actually murder him.
We can surmise that werewolves are more or less immune to direct magical attack, otherwise Severus, with his wand, would not have needed to be rescued from were-Remus, without his wand; and James, with his wand, accompanying Severus, with his wand, would not have been in so much danger from Remus as to be considered heroic. At the same time, purely physical things do affect them, even if those physical things were created by magic. Snape in the Shrieking Shack in PoA magically-generates cords with which he intends to "drag the werewolf", and were-Remus has to physically wrench his paw out of the manacle conjured by Sirius: he doesn't just pass through it or melt it away.
Even though Sectumsempra cuts by magic, the wounds it creates are physical ones which behave more or less as if made with a physical knife. It seems entirely possible, therefore, that Severus learned or invented Sectumsempra after the werewolf attack, or re-designated it from tool to weapon at that point, because he knew it was something which might actually stop a werewolf - whereas a purely magical weapon, such as Petrificus totalus or a Stunning spell, would have no effect.
If he did come up with it as a weapon earlier, though, it may have been because he comes from what looks like a very rough area. He might have learned it (or invented it, if he did) because he could use it to defend himself against Muggle attackers in a way which wouldn't leave obviously magical lesions. As a small child he would have grown up in the shadow of the paedophile serial killers known as the Moors Murderers, who operated in the north Derbyshire/south Lancashire area where Spinner's End is probably situated, so a little paranoia would be natural.
Much has been made of the fact that when Snape caught Harry using Sectumsempra he said "Who would have thought you knew such Dark magic?" But in PoA, Snape also described the Marauder's Map as "plainly full of Dark Magic".
If Snape is always accurate about such things, then Sectumsempra is seriously Dark but so is the Map (a surveillance device which answers as if it could think although - as Arthur said - you can't see where it keeps its brain, and which is activated by swearing a solemn oath of wrongdoing). In that case, young!Snape was indeed working Dark magic but that fact does not set him apart, because so were the Marauders. On the other hand, if he was just being melodramatic when he said that a parchment found in Harry's possession was obviously Dark, he may equally well have been grandstanding when he accused Harry of using a Dark spell.
It's possible that both Sectumsempra and the Map may be Dark, because in DH we see Snape apparently sense the curse on the Peverell ring, which suggests he has some sort of psychic "feel" for such things. But if so that means that the Marauders too were working Dark Magic - and if they, who claimed to hate Dark Magic, nevertheless worked it without apparently intending to,the definition of Dark Magic must be quite wide and vague.
We certainly see that despite their assuming the high moral ground over "Dark wizard" Severus, the Marauders were quite happy to allow were-Remus to roam the countryside, despite several near-misses which put villagers and/or students at potential risk. We are told that werewolves are classed as Dark creatures, that scratches inflicted by a werewolf, even when not transformed, cause cursed unhealing wounds and that the bite of a werewolf turns the victim into a Dark creature in turn, if it does not kill them. But they were quite happy to risk causing Dark injuries to innocent bystanders if it suited the interests of a friend of theirs - just as Severus was willing to excuse whatever Mulciber tried to do.
So, we have a spell which acts as a small-to-medium-sized knife, which could be used as a tool as easily as a weapon. It is classed as a curse by Remus (a DADA teacher, so he knows his stuff), but that doesn't prove it's an evil spell, since some apparently quite benign spells (such as Petrificus totalus) are classed as curses, although they are taught at Hogwarts. It creates normal, physical cuts of shallow-to-middling depth, except that if it amputates a body-part it stays amputated. This last feature seems be common to all curses, rather than a special design feature. The fact that, amputation aside, Sectumsempra does not cause permanent scarring suggests that it probably should not be classed as truly Dark. And it doesn't cut bone even when used with some force, which suggests that it's actually been designed with a built-in safety factor to prevent it from causing amputation.
On the face of it, it seems no nastier than the Reductor curse, which also could be either a tool or a weapon, which probably also causes permanent amputation, and which Harry was freely permitted to learn in fourth year, or than Diffindo which can also cut flesh if you want to use it that way. The only evidence that it is considered Dark Magic depends on comments by Snape himself which apply equally to the Marauder's Map.
Whether he invented it or not, it's not a particularly bad spell, and the spells which do have workings-out, which we definitely know he invented, are all humorous and fairly harmless: rather less spiteful or dangerous, in fact, than a lot of the Twins' bright ideas. Indeed, the fact that a book which is full of young!Snape's home-made spells and notations contains only one mildly nasty curse, which he may well not have invented, is pretty good evidence that he wasn't particularly Dark or unpleasant. If "Dark wizard" equates to "evil wizard", you would expect that a serious Dark wizard, or even Dark wizard wannabe, would come up with something a bit more wicked than making toenails grow.
Furthermore, in his tirade to Harry at the end of HBP Snape says that James used his own spells, plural, against him, and we certainly see James use Levicorpus. If he's speaking accurately then either Snape's spells were so mild that James, who was supposed to hate Dark Magic with such a passion, regarded them as acceptable for his own use - or Snape's spells were Dark and James was a hypocrite who also used Dark Magic when it suited him.
So, other than an off-the-cuff comment by JKR during a Live Chat, the evidence that young!Snape was heavilly involved in Dark Arts rests on his use of Sectumsempra, which is itself not an especially bad spell, and on the word of a biased source (Sirius) who got his information at least in part from a known liar (James). Other equally good, contemporary evidence - the nature of the spells which we know for certain he invented and which James found acceptable for his own use, James's failure to come up with a good excuse for persecuting him, and the fact that Lily only accuses him of having friends who are into Dark magic, not of being into it himself - indicates that his involvement was not as deep or notorious as Sirius claimed. Sirius says that young!Snape arrived knowing more curses than half the seventh years, but even if this is true we've no reason to think that this amounts to knowing more than six curses, or to knowing any curses not sanctioned by the school.
We know that young!Snape used Sectumsempra, whether or not he invented it, and we know it is classed as a curse, and like any curse if it causes amputation, that amputation will be permanent. That aside, it functions as a simple kife, which could be either weapon or tool. We don't know when he designated it "for enemies", but we do know that the first time we see him use it was after his life was threatened by someone immune to magic.
Snape's swishing robes, lowering persona and dramatic introductions to his classes all suggest that he has a streak of dark romanticism a mile wide, and if he did take an early interest in the Dark Arts it was probably not because he was truly vicious but because he was a posy little proto-Goth. As the former proprietor of a small occult shop, I can personally testify that a morbid interest in curses is absolutely normal in boys of that age; and indeed we are shown that first-year Harry shares Snape's interest, and expects that Dudley would too.
Also, Snape was an apparently dirt-poor, working-class half-blooded Slytherin at a time when Slytherin was full of future Death Eaters. A reputation as a super-cool Dark wizard - even if it was mostly air and fluff - and a proven ability to invent his own hexes were probably useful defences against his housemates, as well as against the Marauders.
In any case, a precocious ability with combat spells is seen as attractive and admirable - when it's Ginny's. Neither Harry nor the Twins are seen as Dark, despite the fact that by the end of Deathly Hallows Harry has cast Unforgivables six times, once with partial success and five times with full success, plus a seventh attempt (casting Crucio on Snape), which was interrupted, and the Twins were seriously planning to let off Garrotting Gas which, we are told, is undetectable, and presumably garrottes people. Ginny's comments sound as if it does so fatally. So what makes Severus's controlled and limited weapon so wicked, whilst the Twins' plan to indiscriminately endanger the lives of a school full of children as young as eleven is good-natured fun?
The Twins in fact do some quite appalling things - terrorize their little brother and persecute their older one; induce a toddler to swallow acid and to take an oath which could kill him (admittedly they themselves were very young at that point); beat a child's pet to death for fun; force a lab. animal to eat fireworks; conduct dangerous experiments on eleven-year-olds and Muggles; publicly jeer at an eleven-year-old for having been sorted into what they consider to be the wrong house; commit criminal blackmail; threaten to rape Zacharias Smith with an implement and shut Montague in a broken Vanishing Cabinet where they expect he may be trapped for weeks. He presumably has his wand, so he wouldn't die of thirst, but he could starve or freeze to death or just be destroyed by the damaged magic of the cabinet and he would certainly spend the time shut in a box which is probably too small to lie down in which is a known, and severe, form of torture - all of this to punish him for taking a few points. Rowling herself calls the Twins "cruel" and Snape only "rather cruel". Yet in the eyes of much of fandom everything the Twins do is all right because they have red hair and freckles, and everything Severus does must be wicked because he has greasy, black hair and sallow skin.
Note also that in HBP Dumbledore tells Harry that Snape "returned" to him when he realized the Potters were in danger, and in GoF we see a Pensieved memory of Albus telling the Wizengamot about how Snape "rejoined our side". This does suggest that Dumbledore regarded schoolboy!Snape as naturally of the light, and probably as a potential recruit for the Order.
Later, we see adult!Snape complain to Bellatrix that Dumbledore would never give him the Defence Against the Dark Arts post in case he was tempted back into his "old ways". JK Rowling said something similar in an interview, but this was before HBP and its revelation about the cursed DADA post came out, so she may well just have been planting a red herring. The fact that Dumbledore gives Snape the DADA post once he knows that, one way or another, Snape will be leaving the job in a year anyway suggests that his reasons for not giving Snape the job beforehand were to do with the curse, not because he didn't trust him. The last thing he would want to do would be to tempt Snape towards the Dark Arts just as he himself was about to die, leaving the safety of Hogwarts in Snape's hands; so it's unlikely he really thought Snape would be corrupted by the post.
The fact that Voldemort sent Snape to apply for the DADA post in the first place suggests that the curse would not apply to someone who was acting as his loyal agent, or at least, Dumbledore would reasonably assume that it wouldn't (although in fact Barty Jnr ended up Kissed). So Dumbledore's reasons for not giving Snape the post were two-fold. He didn't want Snape to suffer what might be severe consequences as a result of the curse, but he also didn't want Snape's true loyalties to be revealed, since he would expect that if Snape took the DADA post and then incurred the curse, that would tell Voldemort that Snape wasn't his man.
On the other hand, Bellatrix must find the idea of Snape as a Dark Arts practitioner to be feasible, if his explanation to her as to why he was never given the DADA post was to have any credibility. So he must have had at least some reputation for being into the Dark Arts when he was a Death Eater, or at least he didn't actually have a reputation for not being.
When we see child!Severus interacting with Lily and Petunia, he tells Tuney he wouldn't spy on her because she's a Muggle - but this is a reasonable observation, since the very reason he's been spying on Lily is because she's not a Muggle, but somebody like himself. We would not think that the only Francophone child in a neighbourhood was racist for being preferentially interested in meeting another French child - somebody they could really talk to, who would understand them - for the first time. And he just says "You're a Muggle", albeit in a spiteful tone - he doesn't say "just a Muggle" or "only a Muggle".
It's obvious that in this scene he thinks being a Muggle is less interesting/worthy than not being, but no more so than you'd expect given that Muggles are defined as people who lack the skills in which he is interested. There's no suggestion he regards them as inferior in any other way. Later on when he is angry about Tuney he says "She's only a -" and then stops himself, and the next word might have been going to be "Muggle" - but it could equally-well have been "spiteful little cow".
Even if the next word was going to be "Muggle", there's no indication that he was any more racist than Hagrid, who calls Vernon "a great Muggle" (twice), and describes the Dursleys collectively as 'a family o' the biggest Muggles I ever laid eyes on.' Hagrid, clearly, means something rather more insulting than just "person without magic", but nobody seems to hold it against him.
When Lily asks Severus if being Muggle-born will make a difference to her at Hogwarts he replies by saying that it won't and "You've got loads of magic", so he seems to be interpreting the question as being about her magical ability. The fact that he hesitates for a moment before answering may indicate that he's aware she may encounter prejudice, and isn't sure whether he should tell her about that or not - but since he assures her that it won't make a difference, we know that if he's been raised with prejudices himself he's trying to overcome them.
He assumes automatically that he will be in Slytherin, which means either his wizard family are Slytherins or he has a personal passion for Slytherin, yet he hopes Muggle-born Lily will be in Slytherin too - so obviously he has not been indoctrinated with any "Slytherin is the house for the pure of blood" agenda. Indeed, since his mother married a Muggle, it seems unlikely she was especially prejudiced against Muggles (even if she went off her husband in the end), or that she would fill her half-blooded son with pure-blood prejudices.
It is an anomaly that Severus is so keen on being in Slytherin, yet knows so little about it that he doesn't know that a Muggle-born would be very unlikely to Sort to Slytherin. I would suggest that he already had an interest in Potions and that his mother, who was not a Slytherin, had told him about the Hogwarts Potions master and head of Slytherin, Horace Slughorn, who had no racial prejudice and who could advance the career of clever little boys, even if they were plain and poor and half-blooded. Perhaps she'd been in the Slug Club herself, and Slughorn had been supportive about her decision to marry a Muggle. Severus's own home-life was obviously deeply unsatisfactory, so the idea of a father-figure who would encourage his studies must have seemed highly attractive - and if his mother didn't tell him otherwise, he would assume that Slytherin itself was as prejudice-free as its head of house.
So, the idea that he was racist as a pre-teen rests on the fact that he was more interested in making contact with a child who had magic than one who didn't, and that he may possibly have been aware of the existence of prejudice against Muggle-borns, although not of its true extent within Slytherin.
At the end of fifth year, Lily accuses Severus of calling all Muggle-borns Mudbloods, yet in the bullying scene, James does not justify his attack on young!Snape on the grounds of his racism, even though that would have been a perfect excuse to offer to Muggle-born Lily. All James could come up with was "he exists", at a point at which a good excuse would have seriously improved his chances with Lily. This suggests Snape was not a notorious racist, and was probably just using bad language he had heard from his housemates, who we know included many future Voldemort supporters.
By that point, if Lily is to be believed, he does often use racist language - yet he continues to be best friends with Lily, and we have not seen her accuse him of being racist before. After the underpants incident she seems to be assuming that he is a genuine racist who makes an exception for her, since she says to him "But you call everyone of my birth Mudblood, Severus. Why should I be any different?" But since she refuses to allow him to answer, we don't know whether his reply would have been the essentially racist "But you're special, you're not like the rest"; or "My mates in Slytherin all say it and I've just got into a bad habit"; or even "I only say that because my housemates would batter me if I didn't: I'm in enough danger already because I hang around with you". He is, after all, surrounded by snobby pure-bloods and junior Death Eater wannabees who know where he sleeps.
Calling Muggle-borns in general "Mudblood" could even be a bad-taste joke on his part. He made a joke out of his own half-blood status, after all, and Lily at least is well aware that he's a half-blood, and has tolerated his use of the expression for some time. It's not clear whether, by calling himself the Half-Blood Prince, he's saying "I may be only a half-blood, but at least I'm half a Prince" - or whether the Princes were pure-blood fanatics, and by proclaiming his half-blood status he's sticking two fingers up to them.
The fact that he had friends who were Death Eater wannabees, and later became one himself, might suggest that he shared their racist views: except that JK Rowling has said at interview that one of the reasons Snape joined the Death Eaters at all was because he thought doing so would impress Lily. That suggests he really wasn't aware of the full extent of their racism (if, indeed, they were all that racist - more of this anon, but the evidence for the Vold War One Death Eaters having a strong prejudice against Muggle-borns, as opposed to Muggles, is weak). And indeed, given that he's a half-blood, if the Death Eaters wanted to recruit him they would probably play down the racist angle.
[In any case the Death Eater agenda at that time seem to have been much less racist than it would become in Vold War Two. Hagrid, an Order member, knows of no good reason why Voldemort would not try to recruit Lily, a Muggle-born, and in fact JK Rowling said at interview that he did try to recruit her.]
It's clear, at any rate, that Lily had tolerated Severus using the M-word for some time, so if she thought he was being racist she didn't care much until he applied it to her. And clearly she gave him confusing signals, by suddenly making a hanging crime out of something she had tolerated before.
So why did he call Lily herself a Mudblood during the bullying scene?
To begin with, he fancies Lily and he knows James does too, so he wants to impress her and instead he has just been made a fool of in front of her, by a rival for her affections. He would have felt the way Harry felt when Cho walked in on him two seconds after Neville's pet plant showered him with Stinksap, except with a whole extra layer of humiliation and rage. And we know he tends to lash out when he's distressed.
Then, Lily smiled for a moment when she saw him hung up with his underpants on display. Possibly he had humorous legs, but even so it was insensitive of her to smile when he was in so much misery and humiliation, and it would have made him feel much worse and much more dishonoured in her eyes. He had reason to be angry with her, especially as she had been a witness to the whole of the bullying incident and yet hadn't intervened at once.
Some people take the fact that Lily's attention was on James rather than on Severus as proof that she was flirting with James over her supposed best friend's misery. Personally I think it's understandable she was watching James, since he was the one who was armed and threatening to hex her, but nevertheless JK Rowling has hinted that she was flirting with James in that scene, even if only subconsciously. That, again, would make Severus angry and bitter - at least as justifiably angry and bitter as Ron and Hermione were when they were hexing and insulting each other.
It is also quite possible that Severus's drawing James's attention back onto himself by shouting at him, and disowning Lily by insulting her to James, was an attempt to get Lily out of a risky situation - since James had just threatened to hex her. Severus knows that Sirius, at least, is a potential killer, and he seems to believe - rightly or wrongly - that James was in on the attempt to kill him, until he got cold feet. So as far as he is concerned, Lily is being threatened with violence by someone she refuses to believe is truly dangerous despite his warnings, so he will be angry about her taking stupid risks and ignoring his warnings, as well as protective of her.
And again, working-class, half-blooded Severus must already have been in a precarious position in Slytherin, and if he had allowed himself to be rescued by a Muggle-born Gryffindor witch his housemates would probably have punished him - and at least the Marauders couldn't get at him while he slept. Lily's intervention must have terrified him.
Why did he use the words "filthy little Mudblood" - which is, of course, much more racist-sounding than just "Mudblood" on its own?
There are times when we see the words "filthy" or "filth" used as a definite racial slur - a literal suggestion that somebody's blood is dirty. Draco refers to "Mudblood filth", so when he calls Hermione a "filthy little Mudblood" he probably intends to imply that she's filthy because she's a Mudblood. Tom Riddle refers to his "filthy Muggle father". Bellatrix calls Harry a "filthy half-blood" and Hermione "lying, filthy Mudblood", and offers to cut her to see how filthy her blood really is, so she definitely means "filthy" as a racial slur.
Then there are cases which are more ambiguous. Walburga Black's portrait rants repeatedly about "filth", "filthy half-bloods", "children of filth", but she also says "Mudbloods and filth", implying that these are two different things in her eyes. Yaxley calls Muggle-borns "such filth" but it's not clear whether it's a specific racial slur or a more general insult. Marvolo (and sometimes Morfin) Gaunt raves about "filthy Muggles" and refers to "a filthy, dirt-veined Muggle", which is clearly a racial slur, but he too also says "Muggles and filth" as if they were different categories of things, and at times he speaks as if he thinks Muggles are literally dirty, not racially, metaphorically dirty: "grub on the floor like some filthy Muggle"; "I expect you've wiped the Muggle's filthy face clean for him". Kreacher calls Harry a "filthy friend of Mudbloods".
Then there are plenty of cases where "filth" and "filthy" are used and they emphatically aren't racial insults but general swearwords or derogatory remarks, equivalent to words like "bloody", "fucking" or "rotten". Lee Jordan calls a cheating Quidditch player a "filthy, cheating b --". Sirius calls Peter a "cringing bit of filth". Harry refers to Snape's "filthy hands" (and doesn't mean that they are dirty). Filch calls Peeves a "filthy pilfering poltergeist" and the students "filthy little beasts". Both the real Moody and the false one, for separate reasons, call the Death Eaters "filth". Blaise Zabini calls Ginny "a filthy little blood traitor". Ginny calls Ron a "filthy hypocrite", twice. Viktor refers to Grindelwald's "filthy sign". One Death Eater calls another a "lying piece of filth". Bellatrix calls Greyback a "filthy scavenger", and Travers refers to "filthy gold". And JK Rowling herself called somebody a "filthy, filthy liar", apparently in jest.
So, when Severus calls Lily a "filthy little Mudblood", it's ambiguous whether he means it in the extremely racist sense of "person who is contaminated and dirty because of their Muggle blood", or just "rotten little Mudblood". The latter case would still be racist, of course, but much less so, since "Mudblood" is an expression in common currency and the person using it is himself half Muggle. Lily probably heard it as "contaminated and dirty"; but since the only other time we hear Snape call someone "filthy" he's describing James, a swaggeringly upper-class pure-blood, it's very likely that he just meant it as a generic insult like "rotten" or "bloody".
Given his precarious position in Slytherin and his persecution by the Marauders, Severus needed all the allies he could get. Yet the Marauders repeatedly attacked him four on one and nobody apparently came to stand with him. The Marauders probably used the Map to get him on his own: but that wasn't the case in the Pensieve scene, yet he was isolated. So his Slytherin friends were either not present, not in his year, or not good friends.
Of the crowd we're told he hung around with, Bellatrix and Lucius, at least, were a lot older than him. Lucius was born between September 1953 and September 1954 (he was 41 in mid-September 1995), while Snape was born in January 1960, so Lucius was more than five years older than Sever us, and Bellatrix was born probably in the autumn of either 1951 or 1953, depending on whether or not you accept JKR's doodle of the Black family tree as canon (see accompanying essay on Birthdates in the Harry Potter universe). One wonders whether they were befriending or exploiting Severus: it's quite possible Lucius abused him.
Sexual relationships between boys are common at British boarding schools, and even commoner in people's idea of British boarding schools. The two concepts are so linked in popular belief that JK Rowling may well be hinting at it deliberately. Sirius certainly seemed to be digging at some sore point when he called Snape Lucius's "lapdog", although if young Severus was Lucius's victim and Sirius knows it, Sirius is being exceptionally vicious even for him.
On the other hand adult Lucius probably regards Snape as a friend, and Narcissa certainly does, so if there was a sexual relationship Lucius at least doesn't see it as having been abusive. But if they did have such a relationship, Snape would have been so much the younger that even at best there would always be a strong suspicion of exploitation.
As for Avery and Mulciber, we know Severus hung around with them, and like Remus he made excuses for his mates' dodgy behaviour; but they probably weren't very close friends, since we know the Marauders were still persecuting him four to one after he started hanging around with them. Lily accuses him of wanting to join Voldemort like his "precious little Death Eater friends" - but she doesn't allow him to answer, so we don't really get to know if she was right at that point.
If we accept JKR's interview comment that Snape joined the Death Eaters partly to make himself look cool, thinking that that would impress Lily, then we must assume from this that he didn't expect the Death Eaters to be actively murderous towards Muggle-borns. Presumably they played down any racist agenda because he was a half-blood - and they must have known that he was, since his parents' marriage had been in the Daily Prophet. And indeed, JKR has said that the Death Eaters actually tried to recruit both Lily and James when they left school, and Hagrid, an Order member, thinks it's surprising if they didn't, which argues that at that stage the Death Eaters really weren't officially prejudiced against Muggle-borns, or certainly not in a way which appeared to be life-threatening.
We are told that, for years, young Regulus (who was about two years younger than Snape) "talked of the Dark Lord, who was going to bring the wizards out of hiding to rule the Muggles and the Muggle-borns". So there was an awareness that Voldemort's plans would result in the Muggle-borns possibly being second-class citizens, but also that he meant to make magic publicly known and acceptable to Muggles, which would have advantages for Muggle-borns as well as pure-bloods. And there's no suggestion Regulus thought mass slaughter was on the agenda, so presumably Severus didn't either.
And in any case - who in Slytherin at that time didn't hand around with future Death Eaters? There seem to have been so many that it would have been extremely difficult for any Slytherin not to hang around with future Death Eaters.
The bullying which we see young!Snape suffer is particularly psychologically nasty, and the nickname "Snivellus" was established on their very first day at Hogwarts, i.e. the bullying has probably been going on for the whole of Snape's schooldays. The choice of nickname also implies that the Marauders can make Severus cry, and enjoy doing so - but that could be spurious, since they gave him the nickname on the train to mock him for sticking up for himself.
Either way, hanging him upside-down in public and pulling his pants off, or even threatening to do so, is a minor form of sexual assault. When he swears at them, James forces him to eat soap - effectively saying to him "You're so low, we can do anything we like to you and you aren't even allowed to protest." The incident on the train on their first day was of a piece with that - James made an unprovoked, sneering remark about Severus, and then when he responded in kind James escalated to outright jeering, again saying, in effect, "I can say or do whatever I like to you and you're not allowed to defend yourself," and that has evidently been James's attitude from first to last. This is the kind of bullying which often ends in the suicide of the victim.
And to cap it all, James then tells Lily, in Severus's hearing, that Severus's crime is that he exists - letting him know that there is nothing he can ever do or say which will get the bullies off his back: except to leave Hogwarts, kill himself, kill them, or get the bleeders expelled.
As to what JKR herself thinks of the Marauders' behaviour, it's probably no coincidence that Dudley's gang includes a boy called Piers (an old form of the name Peter), who resembles a rat and who pins Dudley's victims so Dudley can hit them.
We can see from the order of events in Deathly Hallows that the Marauders, including James, went on persecuting Snape with great cruelty even after Sirius had nearly murdered him, and James had saved him. This shows almost unbelievable shallowness on their parts - the shock of having nearly killed a classmate evidently had no effect on their behaviour at all, nor did the gravity of what they had done register with them. Clearly, Snape was right to think that James saved him to protect the Marauders, not out of any concern for him.
We know that the hex-war between James and Severus continued into seventh year, and Sirius and Remus claim that Snape was the aggressor by that point. It's true that even if the Marauders left Snape alone he probably would go on hexing them until he'd proved to his own satisfaction that he'd won. Snape says at the end of HBP that James only ever attacked him four on one: we don't know if this means that all four Marauders were still pursuing him in seventh year; or whether he's forgetting that James sometimes came at him one on one; or whether he indeed doesn't see their rivalry in seventh year as being attacks on himself by James.
However, we know that James concealed his continuing hex-war with Snape from Lily. If it had been self-defence on James's part, or even evenly-balanced, why lie to Lily about it? And the fact that he was able to conceal it from Lily strongly suggests that James picked the venue for their confrontations, using the Map, and that he was the main or even the sole instigator.
We also know that James was head boy in seventh year, and that he had the power to punish Snape for breaking the rules (we see that Percy as head boy is able to give out quite stringent punishments), yet he apparently never stopped Snape from hexing him by e.g. putting him in detention. The best interpretation one can put on James's behaviour here is that he thought defending himself by pulling rank would be dishonourable or cowardly, and the worst, that he didn't punish Snape because he himself had been the aggressor and he didn't want to anger Snape into telling on him; but even at best he was complicit in their hex-war at a time when it was his duty as head boy to prevent that sort of behaviour. Either that, or their seventh year combat was conducted legitimately at some sort of duelling club, in which case it was no fault in either of them.
Snape, Remus and Sirius all confirm their long-standing hex-war, and yet we do not see any sign of it in the detention-notices which Harry copies in HBP, although he sees other cases of the Marauders hexing people. He never apparently comes across Snape's name, either as victim or attacker. This suggests that the Marauders used the Marauder's Map (developed some time after they became Animagi in fifth year, and lost to Filch some time before the end of seventh year), or a precursor of it, to catch Snape where there were no staff witnesses. But Snape had no such Map, so if he'd stalked them as pro-actively as they stalked him he would have been caught and presumably given detention at least sometimes. That suggests that Snape mostly just hexed them in self-defence when they had cornered him, after they had made sure the coast was clear.
Snape did indeed join a terrorist organization. However, teenage boys are prone to idiot politics, and extremists routinely target lonely, troubled teenagers, offering companionship and respect. There was a lot of peer pressure on him to join, since many of his associates from school became members; he has a darkly romantic streak which might have made an outlawed, proscribed group seem appealing; and he was intensely nosy. He didn't necessarily join because he wanted to terrorize people: he may have joined "just to see", and then found that there was no way out.
According to JK Rowling, Snape was attracted to "the dark side", but he was attracted not because he was dark himself but because he was insecure, and thought that "the dark side" was cool and would give him something to belong to.
Or, as libertyelyot put it: "...he was no more evil in his youth than the lads who take up wearing eyeliner and listening to Nine Inch Nails because their souls are so dark, man. But because he had nobody to talk to about anything, it all went so much further than he ever intended."
We also don't know how the Death Eaters presented themselves to new recruits. They must have had some policies which sounded superficially reasonable, or they wouldn't have garnered so many members; and they probably told potential recruits that any atrocities were the work of an unrepresentative fringe element, and not authorized by charming, plausible Tom. If we are to believe JKR's statement that Snape joined the Death Eaters partly because he thought it would impress Lily, then they must have played down the racist angle very much, until he was Marked and it was too late for him to get out - if, indeed, the racist angle was all that marked at that time.
Kreacher says that in Vold War One Regulus understood Voldemort to be going to overturn the Statute of Secrecy, and bring wizardry into the open to "rule the Muggles and the Muggle-borns". Dumbledore says that according to Voldemort's "creed" purebloods are "the only kind of wizard worth being or knowing".
On the other hand, Hagrid, a member of the Order of the Phoenix in Vold War One and somebody who was actually at school with Voldemort, does not know of any reason why Voldemort would not try to recruit a talented Muggle-born. As far as he knows the Death Eaters' anti-Muggle-born policies were not so oppressive as to exclude Muggle-borns from holding down jobs, even jobs with the prospective new government. The model seems to be apartheid rather than genocide.
And in fact, JK Rowling has said at interview that Voldemort did try unsuccessfully to recruit Lily, and that refusing to be recruited was one of the ways in which she thrice defied him - which hardly suggests that the Death Eaters were openly genocidal or even hugely oppressive towards Muggle-borns, or that Severus could predict that they might become so - especially as like most wizards he had little Muggle education, and wouldn't know much about the Nazis or South Africa. Their extreme anti-Muggle-born agenda in Vold War Two seems to have been Umbridge's personal hobby - perhaps inspired by her personal hatred of Hermione.
Sirius says in OotP that 'there were quite a few people, before Voldemort showed his true colours, who thought he had the right idea about things ... they got cold feet when they saw what he was prepared to do to get power, though.' The context suggests that what Sirius means is that people like his family (that is, well-informed Dark pure-bloods at the heart of wizarding society) knew Voldemort wanted to exclude Muggle-borns from positions of power in wizarding society, but didn't know he meant to kill them if, indeed, he did, nor that he was prepared to gain power through terrorism.
It seems unlikely that a marginalised half-blood teenager would have been better-informed than the Blacks, or an Order member like Hagrid, so we can assume that Severus at least didn't know in advance that the Death Eaters were wholesale killers, or that their racial theories were actually or potentially murderous - if, in fact, either of those things was the case.
Also, prior to Shacklebolt's appointment as Minister, British wizarding society routinely subjected prisoners to life-threatening physical neglect, and to extreme psychological torture by Dementor, until the Dementors downed tools: Azkaban under the Dementors was a sort of death-camp which few survived for long. Nobody seems to think that the Ministry's order that Sirius be Kissed is unprecedented, so the government was - at least on rare occasions - prepared to execute people by sucking out and perhaps destroying their very souls, leaving their still-living but mindless bodies as a ghastly, heartbreaking burden on their loved ones. The right to a fair trial, or to a trial at all, was very fragile in wizarding society; we're never shown any sign of an established democracy in the wizarding world, but only the sort of election-by-public-acclaim found in ancient Rome; and at about the time Snape took the Dark Mark the Aurors were killing and torturing suspects with Ministry approval, and there was little to choose between the Head of the Department of Magical Law Enforcement and the Death Eaters.
We are not talking about a free democracy menaced by terrorist insurgents: more like the sort of South American country where the government in City Hall is nearly as brutal as the rebels in the hills. And although the Death Eaters were more racist than the Ministry as regards Muggles, they were actually less racist as regards non-humans such as werewolves and giants. Even if that was just a ploy to win non-human support, it may have enabled them to present themselves to potential recruits as being the faction who were against unreasonable prejudice. Joining the Death Eaters would therefore not seem as obviously terrible a choice at that time as it does in hindsight.
Nor was joining the Death Eaters an unpopular, obviously perverse choice. Remus says that in Vold War One the Death Eaters outnumbered the Order of the Phoenix about twenty to one. The Order group photograph which Moody shows to Harry was taken some time in July 1981 (see When did the Potters go into hiding?) and at that point there were at least twenty-one Order members named as being in the photograph: Moody himself; the two Dumbledore brothers; James and Lily Potter; Frank and Alice Longbottom; Dedalus Diggle; Marlene McKinnon; Emmeline Vance; Remus Lupin; Benjy Fenwick; Edgar Bones (and possibly Amelia Bones too); Sturgis Podmore; Caradoc Dearborn; Hagrid; Elphias Doge; Gideon Prewett (and possibly Fabian Prewett too); Dorcas Meadowes; Sirius Black and Peter Pettigrew - and that's assuming that Moody named everybody who was in the photograph, which we aren't told. Arabella Figg and Mundungus Fletcher were also part of the "old crowd", and Minerva McGonagall may have been: she was certainly a member in Vold War Two, and was involved in transporting baby Harry.
So not counting Snape, there were at least twenty-two Order members at that point - twenty-four if Minerva was already a member and you include Peter. Five were killed before the end of the war, at which point there were then either seventeen or nineteen members. So towards the end of the war the Death Eater army numbered between about three hundred and forty (20 x 17) and four hundred and eighty (20 x 24).
'There's me,' said Moody, unnecessarily pointing at himself. [cut] 'And there's Dumbledore beside me, Dedalus Diggle on the other side ... that's Marlene McKinnon, she was killed two weeks after this was taken, they got her whole family. That's Frank and Alice Longbottom --' [cut] [cut]'... and that's Emmeline Vance, you've met her, and that there's Lupin, obviously ... Benjy Fenwick, he copped it too, [cut] [cut]'That's Edgar Bones ... brother of Amelia Bones, they got him and his family, too, [cut] ... Sturgis Podmore, [cut] ... Caradoc Dearborn, vanished six months after this, [cut] ... Hagrid, of course, [cut] ... Elphias Doge, [cut] ... Gideon Prewett, it took five Death Eaters to kill him and his brother Fabian, [cut] [cut]'That's Dumbledore's brother Aberforth, [cut] strange bloke ... that's Dorcas Meadowes, Voldemort killed her personally ... Sirius, when he still had short hair ... and ... [cut] Harry's heart turned over. His mother and father were beaming up at him, sitting on either side of a small, watery-eyed man whom Harry recognised at once as Wormtail, [OotP ch. #09; p. 158]
'You weren't in the Order then, you don't understand. Last time we were outnumbered twenty to one by the Death Eaters and they were picking us off one by one ...' [OotP ch. #09; p. 161]
The wizarding population of Britain is between three and a half thousand (JKR's own estimate, which doesn't really fit what we see in the books) and ten thousand (my estimate). Say that there were around four hundred Death Eaters or active Death Eater supporters, and that they were all human and British: that means that somewhere between one in twenty-five and one in nine of the wizarding population was an active Voldemort supporter - of the adult population, perhaps as many as one in seven. Even if you assume more than half of that army was non-human, you've still got a minimum of one witch or wizard in fifty being an active member of Voldemort's forces (although some of those will have been under Imperius).
Scaled up in proportion to the population of Britain, that's equivalent to an army of between one and six million: scaled up to the population-size of the US, between six and thirty-five million. This isn't just a small insane terrorist group preying on a peaceful society, it's a full-on civil war - and yes, one side of that civil war is a minority with at least some degree of a racist agenda, but that's equally true of the American Civil War. Anyone who joined Voldemort was joining a mass movement, and not necessarily any more personally evil than a random selection of Confederate soldiers.
We know, also, that James and Sirius were Order members while they were still at school, or at least they were wannabes. We know this because JKR wrote a prequel vignette for a charity auction, showing James and Sirius wearing phoenix T-shirts and fighting what seem to be Death Eaters, and she said on her website that this scene was set three years before Harry's birth, which places it probably in the summer between their sixth and seventh years. Sirius also claims that James hated Dark Magic, which was probably something he let be widely known, and if they were wearing phoenix T-shirts they were making no secret of their allegiance to the Order either. All of which means that by the start of seventh year, if not before, Severus had good reason to think that the Order of the Phoenix, the party of open opposition to Voldemort, was a party of thugs, bullies and hypocrites who claimed to be against Dark Magic whilst secretly trying to feed a classmate to a Dark creature. This would tend to give him the impression (based on the incomplete information which was available to him) that the Death Eaters were, at worst, no worse than their opponents.
In fact, it's moot whether the Death Eaters were very much worse than the Ministry. Sirius says that Barty Crouch Snr became "as ruthless and cruel as many on the Dark side", which necessarily means that many on the Dark side were no more ruthless and cruel than Barty Crouch: and whilst Crouch authorised the use of the Unforgivables on Death Eater suspects he presumably thought the people who were being tortured and killed were probably guilty, and that torturing and killing them was in the public interest. Nobody has ever suggested that he tortured and killed randomly or for fun, ergo many of the Death Eaters also did not torture or kill for fun, but only because they thought it served their own idea of the Greater Good.
We are told that there were many cases of Muggles and wizarding opponents being tortured by the Death Eaters during Vold War One, but we do not know what is meant by this. Fanon assumes it refers to terrible atrocities and I've even used this in some of my own fics, but we see Voldemort characterise the baiting of the Roberts family at the World Cup - which was only marginally worse than what the Marauders did to Severus - as "Muggle torture", which means we can't know whether the tortures inflicted by the Death Eaters, generally, were mind-warping agonies or a bit of aggravated bullying.
Other than Hannah Abbott's mother (for whom we have no background) all the deaths of witches or wizards due to Death Eater activity and that we know anything about are deaths of people who were directly opposing Voldemort in some way (e.g. Aurors and Order members), or of their immediate families. And except for one case of an attack by Greyback, who is a maverick, even where family members were killed we're not told whether this was an act of intentional cruelty designed to spread terror, or simply a matter of blowing up a target and killing family members as inadvertent collateral damage, as happened when the IRA murdered Lord Mountbatten.
In fact, the Death Eaters seem to be loosely based on the IRA and other British terrorist organisations. I go into this in more detail in my essay on British cultural references in the Harry Potter books, but basically many of the events and issues surrounding the Death Eaters and the Ministry's response to them are close parodies of real-life events connected with terrorism in the British Isles 1968-1996, and how our security forces dealt with it. The masks the Death Eaters wear (close-fitting black cloth hoods with large eye- and mouth-holes) are modelled on IRA masks, and even the timing of many aspects of the Death Eaters' campaigns correspond with the timing of terrorist campaigns in the real-life U.K..
On the whole, British terrorist organisations rarely targeted civilians, although they were prepared to kill them if they got in the way. The last major terrorist attack in mainland Britain, in summer 1996, took out much of central Manchester: there were eighty thousand people in the blast zone and not a single death, because the IRA warned the police in time to evacuate them. Hence, the fact that the Death Eaters were terrorists, and very willing to kill people they regarded as legitimate targets, does not necessarily mean that they targeted innocent bystanders as well. They may have done, but it's an open question, and we cannot therefore say with confidence that Severus joined an organisation which targeted civilians.
[There were at least some Vold War One killings of Muggles by Death Eaters, but since wizards originally went into hiding because of the 17thC witch-burnings and we're told (in Beedle) that some wizard children are still raised on stories of Muggle persecution, they may have felt they were attacking a powerful enemy rather than persecuting innocent inferiors. It should be noted that the rise of Voldemort happened at a time when many Muggles were themselves scared that Muggle military technology was going to wreck the whole world and bomb humanity back to the Stone Age.]
Severus, of course, grew up in the Muggle world. So far as we know, until he left school and (presumably) got a job he had no contact with the wizarding world outside of the protected environment of Hogwarts, so he knew nothing about the Death Eaters except what he read in the press (which no intelligent Briton trusts) or heards from his schoolmates - many of whom were pro-Voldemort. And like every Briton of his generation he would have grown up with terrorism as part of the constant backdrop of his life, and he would be conditioned to expect that a terrorist organisation would behave like the IRA - that is, that it wouldn't gratuitously target uninvolved civilians, or kill bystanders except by accident - whether that was true of the Death Eaters or not.
Many fanwriters have assumed that young Severus was deeply affected by the fact that Sirius tried to kill him, and wasn't punished for it; and that this pushed him towards becoming a Death Eater.
We don't in fact know if that was what happened. We know that as an adult Severus believed that Sirius had meant him to die, because he refers to the werewolf incident as "a highly amusing joke on me that would have resulted in my death if your father hadn't got cold feet at the last moment. [cut] Had their joke succeeded, he would have been expelled from Hogwarts" - that is, he believes that his death would have represented the success of the "joke". But we don't know whether he believed at the time that Sirius had really meant him to die, or whether he only came to believe that after he was told (wrongly) that Sirius had killed thirteen people.
We also don't know whether Sirius was punished or not. We do know he wasn't expelled, but I suspect that the staff cut him a lot of slack because the incident coincided closely with his breaking away from his family, and they thought he was having some kind of mental breakdown. [He left home when he was "about sixteen", and bought himself a flat when he was seventeen - from the sound of it, probably soon after he turned seventeen - and I show in the separate essay on Birthdates in the Harry Potter Universe that his birthday falls during the autumn term, and probably in September or October, so he probably bought his flat round about Christmas of sixth year. In between his leaving home and buying the flat there had been two or three holidays, plural, which he spent staying with the Potters, so he must have left home some time fairly early in fifth year.]
We know that in June of their fifth year Sirius felt free to persecute Severus in public, and evidently wasn't being closely watched, and wasn't put off by any fear of punishment - but he may have been psychopathic enough not to be affected by punishment anyway. We certainly see, from Filch's files, that James and Sirius received many, many detentions for hexing people, and it didn't modify their behaviour.
We know the werewolf incident happened before the underpants incident, and that Sirius was sixteen at the time - but Sirius turned sixteen early in the first term of fifth year (see Birthdates in the Harry Potter universe). For all we know, the werewolf incident could have happened in November, and Sirius could have been punished severely (short of expulsion) and watched like a hawk for six months - although not closely enough to prevent him from sneaking out and turning into a dog! There is certainly a hint that it happened prior to James's birthday on 27th March, because when Harry quizzes Remus about the underpants incident, Remus says that James was fifteen at that time. That's definitely untrue but it may mean that Remus's mind naturely dwells an the werewolf incident, and that James was fifteen then. So it is likely that at least three months elapsed between the two - long enough for the staff to have taken their eye off the ball, assuming it was ever on it.
However, we can say that if it was the case that Severus believed from the outset that Sirius meant to kill him, and if it was true that Sirius was hardly punished, then that would have a scarring effect on his psyche. It would make him feel that the "light" side saw his life as of no account, and that the Death Eaters represented his greatest hope of safety - especially as according to JKR's prequel James and Sirius seem to have already been Order members in sixth year, and to have made no secret of their membership, and yet we know that James at least was still persecuting Severus. It may well be that JKR intends this to be the case, because if James drove Severus to become a Death Eater, it would mean that James's callousness brought about his own death; just as Sirius's harshness to Kreacher brought about his.
At any rate, we know that Severus believed - rightly or wrongly - that James and Remus had been involved in the planning of the incident and that James had only changed his mind at the last minute, for selfish reasons: so it would burn him to see Remus treated as innocent and James as a hero for saving him. The fact that James then kept right on persecuting him, in what we see was a very cruel and to some extent sexually-abusive way, would reinforce his conviction that James had saved him for venal reasons; and when James became Head Boy despite still hounding him on the side, Severus must have felt understandable outrage and disgust - and possibly helplessness too, because who would believe him if he complained that the Head Boy was secretly persecuting him? So whether Sirius was punished or not, the whole situation would encourage Severus to feel excluded and rejected by the Order side, and desperately in need of other allies.
How long was Snape a true Death Eater?
We know that the prophecy, which was assumed to relate to Harry and which Snape overheard and conveyed to Voldemort, was made in 1980. During the fight at the Ministry at the end of OotP, in mid to late June (because it was just after the end of OWLs) 1996, Harry looks at the globe containing a record of Trelawney's prophecy about him, and sees that its label is dated "some sixteen years previously". The next day, Dumbledore says that the prophecy was made "On a cold, wet night sixteen years ago." The prophecy itself refers to one who "will be born", so we know it was made prior to Harry's birth at the end of July - so we can definitely say it was made during the first seven months of 1980.
Then, we know that Sybill Trelawney was appointed as Divination mistress some time after the prophecy was made. If the prophecy was made in the summer of 1980 Trelawney would have started work in September 1980. Yet, in September 1995 she tells Umbridge that she has been teaching at Hogwarts "Nearly sixteen years." She might exaggerate her tenure a bit, but it would be a dangerous and damaging lie to tell if she really had been teaching only fifteen years and a couple of weeks. Shortly afterwards Trelawney speaks to Parvati of her "sixteen years of devoted service", and when Umbridge sacks her, in March 1996, she cries "I've b -- been here sixteen years!" Altogether it sounds as if Trelawney really did start teaching at Hogwarts earlier than September 1980, so we can guess that she started in either the winter or spring term, and the prophecy was made during the Christmas or Easter holidays, in January or March 1980.
We know Snape was a true Death Eater at the time that the prophecy was made, that he defected to Dumbledore after the Potters were targeted, and that the Potters went into hiding because of Snape's warning. Some readers have assumed that the Potters only went into hiding when the Fidelius was cast, a week or two before their deaths, and that Snape's defection therefore occurred just before the end of the war; but I show in my essay When did the Potters go into hiding? that there is very strong canon evidence that they in fact went under cover in two stages, the first occurring many months before the Fidelius was set up: certainly well before Harry's first birthday, and probably prior to February 1981.
This interpretation - that Snape's defection happened well before Harry's first birthday - is supported by the description of the scene in which we see Snape come to Dumbledore and ask him to save Lily. We are told that it is very windy and the trees around them are bare, but there are still leaves blowing in the wind. Unless this is extremely freak weather, this is not the same autumn that the Potters died, because they died at the end of October, and late October and early November is the peak time in Scotland for viewing the autumn leaves, still on the trees. If the trees are bare it's no earlier than mid November, and if there are still leaves blowing around which haven't decayed to mulch, it's probably not later than mid January - certainly not later than March, because by April there would be obvious buds on the trees, and in fact in PS we see a beech-tree at Hogwarts already in full leaf in late March. So we know Snape ceased to be a true Death Eater no later than early 1981.
On the other hand, we can reasonably assume that the defection scene is not taking place in early 1980, immediately after the prophecy was given - even if the prophecy was made as early as January. We assume this because Snape refers to Lily's son, and speaks as if the baby could be killed and yet the mother spared. It's possible that the sex of wizarding children is announced soon after conception, and that he is thinking of Voldemort hexing the child in the womb without killing the mother, in which case this scene could be taking place in January 1980. On the whole, though, it sounds more as if Harry is already born - especially since it was only after Harry's birth that Voldemort could be sure he would be born in late July rather than early August, and fitted the prophecy. Therefore, Snape's defection occurred after mid November 1980 and probably by mid January 1981 - certainly by March 1981 at absolute latest.
So, we know that early in 1980, Snape was a Death Eater, and by early 1981 he had ceased to be one.
We don't know how long Snape had been a Death Eater before hearing the prophecy. It could have been four years - or four days. We know Lily accuses him of being eager to join Voldemort at the end of fifth year, almost four years before the prophecy was made: but since she doesn't really give him a chance to comment, we don't know if she was right or not, or what effect their break-up might have had on his views.
It's probably safe to assume, though, that he wasn't already a Death Eater at that point, unless he'd only joined a few days beforehand, because if he is one Lily clearly doesn't know it, and JKR said he joined partly because he hoped it would impress her. So if he had joined while they were still friends, he would have told her. The earliest he could have become a Death Eater, then, was mid June 1976.
So, we only definitely know Snape was a true Death Eater for about eight months, from March to November 1980, but it is likely that he was one for at least some months beforehand, and possibly for a lot longer. The longest he could have been a Death Eater for was four and a half years, from June 1976 to circa January 1981.
If we assume that his joining the Death Eaters partly in order to impress Lily means that he was hoping to win her back, he probably did join prior to her marriage. Unless she married pregnant (unlikely, as one would assume wizards have very good contraception) or Harry was premature, she must have married prior to November 1979, and Snape became a Death Eater no later than October 1979 - more probably somewhat earlier, since it's unlikely he was still trying to impress Lily only weeks before her marriage. The earliest he could have defected is November 1980, so we know he was a Death Eater for a minimum of thirteen months.
The only other data we have is that in July 1996, Snape tells Bellatrix that at the time of Voldemort's resurrection (in June 1995) he had had sixteen-years'-worth of information about Dumbledore to give to the Dark Lord. He's not referring to his activities since Voldemort was disembodied, because less than fourteen years elapsed between Tom's fall and resurrection. He's not referring to the time since he defected and (according to the line he's spinning Bellatrix) deceived Dumbledore into letting him close, because the earliest that could have been was fourteen years and seven months prior to Voldemort's return. He's probably not referring to elapsed time since he first conveyed the prophecy to Voldemort, either, because the prophecy was made less than fifteen and a half years prior to Voldemort's return. It's unlikely that a potions expert can't do math, yet Snape is linking his period of service to the Dark Lord with something that happened sixteen years prior to June 1995.
The most likely scenario is probably that he joined some time in early to mid 1979, and that he was at the Hog's Head in (probably) January 1980 because Trelawney was right, he really was applying for a job in the hopes that he would then be able to spy on Dumbledore. In order to sound good to Bellatrix he conflated sixteen and a half years as (as far as she knows) a Death Eater, fifteen and a half years attempting to spy on Dumbledore and fifteen years actually doing so into sixteen years of spying.
It is possible that he joined earlier than 1979, and really did begin to spy on Albus in some way in 1979, or very early in 1980 (fifteen and a half years before Voldemort's rebirth). But we have no evidence that he joined that early, and the fact that he has no reputation as a Death Eater makes a short membership more likely than a long one.
The fact that we don't know what Snape did between leaving school in summer 1978 and hearing the prophecy in early 1980 doesn't prove he was working for Voldemort since he left school. We don't know what anybody from that academic year did between leaving school and 1980, except that the Marauders and Lily at some point joined the Order of the Phoenix, and James and Lily got married and had a kid.
We do know, however, that Tom sent Snape to Dumbledore to apply for the post of Defence Against the Dark Arts master. Although he didn't get it, there must have been something in his history which would make him seem an at least possible candidate. We know he was interested in DADA at school, and that Dumbledore was already having to find a new DADA teacher every year, so it could just be that. But there's at least a hint here that he had been working in some field which made him seem like a good choice to teach DADA - perhaps as a curse-breaker or some sort of security operative.
And if Dumbledore really appointed him as head of Slytherin house at twenty-one (which we don't know for sure, but there's no mention of any other head of Slytherin between Slughorn and Snape) then he presumably seemed as if he might have management or pastoral skills. He doesn't appear to have been a prefect, so we can guess that whatever job he did between eighteen and twenty-one involved supervising staff. It's also possible he had shown leadership potential while still at school by running a club of some kind - perhaps coaching other students in Potions, in the way that Harry taught DADA in fifth year.
We also do not know whether Snape was a keen Death Eater until the danger to Lily changed his mind; or whether, like Regulus, he developed doubts soon after joining; but as with Regulus it took a threat to a loved-one to move him from "I wish I could get out of this, but I'm too scared" to "I'm going to get out of this even if it kills me."
Snape is a very noticeable guy. He has long, jet-black hair of a distinctive style and texture (i.e. greasy). His eyes are unusually black. He has excessively pale skin. He has a huge and oddly-shaped nose. He has uneven, yellow teeth. He has a dramatic and noticeable gait.
In the graveyard scene in GoF it says that "Harry saw their eyes dart sideways at each other through their masks" and refers to "the glittering eyes in their masks". But when Harry sees Lucius again in OotP he thinks: "He had last seen those cold grey eyes through slits in a Death Eater's hood", which implies that the hood and the mask are the same thing, and Lucius in the graveyard scene is described as speaking both from "under the mask" and "beneath the hood". At the Ministry of Magic battle we are told that "Black shapes were emerging out of thin air all around them, blocking their way left and right; eyes glinted through slits in hoods", and then later it says of one of these figures that "his mask had slipped so that he couldn't see": which confirms that mask and hood are one.
So, we know that the Death Eaters' masks are simply close-fitting black hoods with large eye-holes, and either a mouth-hole or the lower part of the face left bare (because a masked Death Eater can still kiss his master's robes). We know that Harry is easily able to identify Lucius's voice when he is masked. At the Ministry of Magic battle Harry is able to distinguish the mad look in Bellatrix's eyes, and see that Lucius's eyes are grey - from only a few feet away, it's true, but also in rather poor lighting conditions. In the graveyard scene he can see the Death Eaters' eyes darting from side to side within their masks, again in poor light. So we know that even masked, it would still be possible to see that Snape was a tallish, skinny guy with a prowling walk, pale skin, super-black eyes and an enormous hooter. You would probably see his mouth complete with uneven teeth, and possibly the ends of his long, straight, black, greasy hair.
[We know he is tallish because Narcissa is tall for a woman and yet Snape is able to look down into her face, and because Sirius is described as tall, and although Snape is visibly shorter than Sirius the difference is small enough that Harry only notices it when he sees them face to face. So we can say Snape is probably within the range 5'10" - 6'1".]
In the cave scene in GoF, Sirius says that so far as he knows Snape was never even accused of being a Death Eater. It's slightly ambiguous whether he means that as far as he knows Snape was never formally accused in court (of course, we know he was accused, but after Sirius's own arrest), or that he was never accused even in common gossip. However, Sirius is actually being critical here of the fact that many of Snape's friends became Death Eaters, and he is stressing that the fact that Snape wasn't accused of being a Death Eater doesn't prove he wasn't one: so what is going on here is that Sirius really wants to link Snape to the Death Eaters, but is too honest to conceal the fact that he doesn't have anything to go on except personal suspicion and the nature of some of Snape's friends.
Given that he is actually trying to rubbish Snape, as far as his own intrinsic honesty permits, you would think that if Sirius meant that there were rumours that Snape was a Death Eater but he wasn't formally accused of being one, he would say that. Ergo, he means what it sounds as if he means - that to his knowledge Snape wasn't accused of being a Death Eater either formally, in court, or informally, in gossip.
If Snape had been on a lot of raids, or standing at Voldemort's right hand torturing suspects, surely somebody would have remarked on (and recognised) him. And yet Sirius - who loathes Snape, and who was an Order member with access to inside information - had never heard any accusation that Snape was a Death Eater; and in the Spinner's End scene Bellatrix accuses Snape of being all talk and no action. When Dumbledore asks Snape to kill him, Snape is concerned that doing so might damage his own soul, and when he chides Snape about being squeamish about sending Harry to his death, he asks him how many men and women he has watched die - not how many he has killed. [And Snape replies that latterly - since he ceased to be a true Death Eater, presumably - he has only watched die those whom he was unable to save, thus confirming that he is not somebody who enjoys violence, or even is indifferent to it.]
JK Rowling said of Snape: "He can see Thestrals, but in my imagination most of the older people at Hogwarts would be able to see them because, obviously, as you go through life you do lose people and understand what death is. But you must not forget that Snape was a Death Eater. He will have seen things that...."
That is, she specifies that he has seen deaths while he was a Death Eater, but she does not suggest that he himself killed, and takes pains to point out that the fact that he has seen death doesn't set him apart from the other staff members. It certainly doesn't sound as though she thinks of him as a willing, casual killer.
Nowadays, with the rise of Islamist terrorism with its murderous suicide bombings, I think it's difficult for non-British readers - or even British readers under about thirty - to imagine a terrorist group as anything other than wholesale killers, or to realise that a writer might write a terrorist as anything other than outright evil. But all Britons of my/Snape's/Rowling's generation grew up with terrorism as part of the everyday fabric of our lives, and culturally speaking British terrorism is much more ambiguous. The terrorists were a part of us, of our own culture; they did not usually target civilians; and their goals (on both sides of the grinding civil war that was The Troubles) were intelligible and reasonably sympathetic. That British terrorists were often seen as vaguely romantic rather than villainous can clearly be seen from the fact that there was an open mass-movement in the US to raise money to fund IRA terrorism.
Although hardly anybody outside the terrorist organisations themselves actually approved of their methods, sympathetic media portrayals of individual terrorists were fairly common - the film The Crying Game, for example, or the children's fantasy novel Dogsbody by Diana Wynne Jones, where the heroine's beloved father is a jailed terrorist and the plot ultimately hinges on the fact that the daughter too has the will to kill, although to better ends than her father. A succession of civil wars and uprisings in Ireland - not just The Troubles of the 20thC but other wars for centuries before that - generated memorable ballads about armed struggle, about noble rebels or about the pain and moral ambiguity of being such a rebel, and these were widely sung in folk-music circles even by people with no terrorist sympathies: The Patriot Game; The Wind That Shakes the Barley; Roddy McCorley; The Boys of the Old Brigade. It is against this background - not the background of Islamist terrorism - that Rowling invented Snape. In fact, almost my first thought on reading the Harry Potter books was that Snape's story-arc was a fantasy gloss on what would be a standard plot about a näif teenage boy who joins the IRA in a fit of misguided romanticism, has some kind of epiphany which causes him to realise that their methods are unacceptable, and ends up working for the security services.
So, we know that as a Death Eater Snape did witness killings and/or atrocities, but he may never have taken an active part: he certainly didn't make a habit of doing so, and it is strongly hinted that he never killed until that night on the Astronomy Tower. And we know that latterly, as a spy, he has done his best to stay out of direct physical action, and to save the victims if he could - which tells us that he certainly isn't, as sometimes portrayed in fanfiction, a monster of sadism who used his position as spy to get his jollies.
On the contrary, we see that Dumbledore feels obliged to order him to play his part convincingly in the chase after the false Harries. "If you blow your cover you'll be killed" isn't enough to make him obey, either: the lever Dumbledore uses is that he needs to maintain Voldemort's confidence in order to protect Hogwarts from the Carrows. Evidently, Dumbledore believes that Snape values the students' lives more than his own. And even so, Snape still disobeys - to protect Lupin.
We have no reason to think that Snape knowingly betrayed a baby to its death. The part of the prophecy which he heard just says "The one with power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies." Although the champion has to be young enough for their parents to have defied Voldemort three times, that could have happened in the 1950s - or as recently as last week. There's nothing to say that "the one"'s parents defied Voldemort before "the one" was born: the only restriction is that "the one" cannot be so old that his or her parents were already dead by the time Tom Riddle started on his political career.
There's nothing to suggest that the birth hasn't happened yet (it's only the second half of the prophecy, which Snape didn't hear, which says "will be born"), and "The one with the power ... approaches" sounds much more as if it refers to an adult champion who is on the move and travelling nearer - some witch or wizard in the prime of life, whose parents are known opponents of Voldemort. The fact that the prophecy dwells on parentage and birth-dates might make one think of a child, but the fact that you start by hearing that the one "approaches" would prime the listener to expect that what follows would refer to an adult. Voldemort presumably works out that it refers to an unborn child because he knows - as Snape would not know - whether there are any couples who have defied him three times and who have an adult child born in late July, but there's nothing in the words themselves to say it's about a child.
It has been suggested that Snape should have known the prophecy referred to a birth which hadn't happened yet, because it says "as the seventh month dies" rather than "died". But aside from the fact that it would be difficult, when crouching down listening through a keyhole, to be certain whether one had heard the word "dies" or "died", especially as it was at that point that he was hauled away from the door, random tense-changes for poetic effect are quite common in British prophetic or cod-prophetic writing. For example, the singer-songwriter Alan Stewart adapted some of Nostradamus's quatrains as:
An emperor of France shall rise Who will be born near Italy: His rule shall cost his empire dear -- Napoleron his name shall be.
From Castile does Franco come And the Government driven out shall be; An English king seeks divorce And from his throne cast down is he.
One named Hister shall become A captain of Greater Germany: No laws does this man observe And bloody his rise and fall shall be.
In the new lands of America Three brothers now shall come to power: Two alone are born to rule, But all must die before their hour.
Two great men yet brothers not Shall make the north united stand: Its power be seen to grow And fear possess the eastern land.
Three leagues from the gates of Rome A Pope named Paul is doomed to die; A great wall that divides a city At this time is cast aside....
The fact that these aren't Nostradamus's own words is beside the point. Alan Stewart, a well-known and popular British songwriter of the 1970s/80s, with whose work young Severus might well have been familiar, felt it was appropriate for prophetic language in English to veer erratically between the future and present tense; so there was no reason why Snape should assume that the use of the present-tense word "dies" in Trelawney's prophecy necessarily meant it was referring to something which hadn't happened yet, when the rest of what he heard sounded so much as though it related to an adult champion.
If anything, the fact that Snape was a Death Eater is evidence that he isn't a monster. We have seen young!Snape lash out in rage and bitterness. He was a true Death Eater for at least eight months, more probably for about twenty months, and he's been a fake one for years. All that time, he had opportunities to kill (we know he witnessed killings) and perhaps to torture or rape as well, especially if fanon is to be believed. His comrades probably actively encouraged him to do so. Acting the willing killer would have strengthened his position with the Death Eaters and with Voldemort: doubly important once he became a spy, when any loss of their confidence in him would have resulted in death - possibly in a miserable death by torture. And once he became a spy, he could probably have committed any crime he liked and got a free pardon for it, because it was "necessary to maintain his cover". For years he has had both opportunity, motive and encouragement to give his inner rage free rein. And the only reputation he seems to have managed to acquire is that as a Death Eater he is all talk and no action.
Not to hurt people when you are pottering along with your safe civilian life may indicate nothing but laziness and lack of opportunity. Not to hurt people when you are burning up with rage and you have every opportunity to do so, everyone around you is encouraging you to hurt them and doing so would be to your advantage argues a profound determination not to hurt people.
[His relationship with Lily of course spans his entire life from age nine until death, but I've put it in the "young man" category because the accidental betrayal and Lily's death is so central to the plot.]
Many people think that Snape's attitude to Lily was stalkerish, and this is in part because child!Snape is described as watching Lily with an expression which is "greedy". He is unlikely to have felt anything like sexual desire when he was only nine or ten, though, so presumably his greed was for the company of another wizard child, or to have something beautiful in his grey life - or just to be able to say "I know something you don't know". He does rather like to gloat, and the fact that he would later be Sorted into Slytherin suggests that he was a powerfully ambitious child.
Once they have become friends, he is again described as watching her greedily. Since he's too young for sexual desire his infatuation is presumably of the platonic kind - intense feelings of friendship and admiration. That he already had such strong feelings for Lily, before he was old enough for sex to be involved, in turn means that sex was probably not the main driving force behind his later passion for her. It was not the case that he fancied her, and then he loved her - he loved her, and then he fancied her.
In any case, JK Rowling seems to have a rather negative attitude to desire. Ron and Hermione tear at each other, Albus's desire for Gellert leads to the death of his sister, and Bellatrix's desire for Tom is mania. Child!Snape's greed is certainly no more worrying or dark than teenage!Harry's large scaly chest-monster which flares up when he sees Ginny - who isn't even his girlfriend yet - kissing another boy. And child!Snape's "greed" is Harry's own interpretation, coloured by Harry's experience of what a scruffy, black-haired young boy might feel about a pretty redhead (chest-monsters again), at a point at which he still half thinks that adult!Snape was a murderous Death Eater who was trying to get Voldemort's permission to hunt him down. So it's not surprising that his initial interpretation of the first memory he sees is tinged with negativity.
Child!Snape's approach to Lily is awkward but after telling her she's a witch, he remembers to tell her that that's an OK thing to be. When she asks whether being a Muggle-born will make any difference to her status, and he hesitates before reassuring her that it won't, it's not clear whether he's lying out of kindness, or really doesn't know the answer and is having to think about it, or is glossing over a complex answer about meeting some prejudice but it not affecting her career. He follows it by praising her magical strength, which suggests he has taken her comment to mean "Will being Muggle-born weaken my magic?", and if his hesitation means he is aware that it may cause her problems in other ways, he doesn't want to upset her by saying so. He is kind to her from the first, then, and admires her from the first, even though he is tongue-tied about saying so: he starts to say 'You're not going to end up in Azkaban. You're too --' and then stops and flushes red.
He becomes spiteful to Petunia only after she is spiteful to him, and there is nothing to suggest that his dropping the branch on her was voluntary: it appears to be the same sort of spasm of involuntary magic which Harry used to vanish the glass from the snake's cage or to inflate his aunt, when he too was upset and angry. Lily, however, assumes that he must have done it deliberately, and blames him, even though she herself has wandless magic and must know how it works. Unless, of course, Lily is always in control of her magic, and of herself.
We do not know whether it was Severus or Lily who opened Petunia's letter from Dumbledore: only that (if Lily is telling the truth) he was the one who saw the envelope first. If Lily's comment is to be believed, Severus's main interest in the letter was not nosiness about Petunia, and certainly not malice, but honest curiosity about the workings of the wizarding world, and how a letter sent via the Muggle post office could end up at Hogwarts.
Nor do we know whether he read it or not: only that Lily did. They were presumably both in Petunia's room, but Severus could hardly have been in there without Lily's connivance: and since she went on to read the letter she was certainly not going "How dare you invade my sister's bedroom?" It was certainly Lily who was stupid enough to tell Tuney she'd read her private correspondence. Yet she blames Severus for all of it.
When Lily says that Tuney hates her Severus says "So what?" which seems rather callous - but since his family appear to be at each other's throats all the time he may genuinely not see anything odd about it, especially as Tuney seems to be routinely rather unpleasant to Lily. At any rate he responds to Lily's statement that she doesn't want to speak to him and her "look of deep dislike" with friendliness and a successful attempt to cheer her up.
That he seems hardly affected by her anger here may be a sign of insensitivity on his part, or of a tendency to fantasize her rather than really seeing her. Or it may just be that he is used to people being angry and cold with each other one moment and friends the next because that's how his family are - or because that's how Lily is.
The fact that Lily was already so cold towards him - that she automatically took Petunia's part against him in any dispute even when Petunia was clearly behaving badly, and looked at him with "deep dislike" rather than hurt or anger - suggests that Lily never was anything like as fond of Severus as he was of her. Yet, it was not a case of him pursuing her and forcing friendship on her: we see her apparently excited by his company and by what he is telling her, and she allows him to think of her as his best friend for five years at Hogwarts. That suggests that she was consciously or unconsciously using him as a source of information, rather than really loving him - or perhaps that she was naturally rather cold and her friendship was always conditional and easily lost, to everybody. Or perhaps she did love him, but she was one of those females who believe you should never give a man an inch of leeway (which wouldn't bode well for her relationship with James).
It looks as though Lily was never as warm to Severus as a good friend should be, although he believed them to be best friends. Yet, this was not fantasy on his part. Teenage boys are rarely very good at reading social cues, and he seems to be a lonely boy who probably doesn't have any other very close friendships against which to measure this one. If Lily reassures him that they are best friends - as we see that she does - why would he doubt her?
The scene in the courtyard is especially awkward. Superficially, Severus appears to be being a prat, and Lily certainly thinks that he is. But we must remember what Remus said about the werewolf "prank" - that Severus actually saw him in the tunnel (whether in were or in human form isn't specified), and was bound to secrecy by Dumbledore. It's clear from what Lily says, about "knowing [his] theory" about what's down the tunnel, that Severus has already been speculating, and very probably speculating that Remus is a were: but now he is sworn to silence and unable to tell Lily about the new evidence he has.
When Lily accuses Severus's Slytherin friends of performing Dark Magic and he replies "What about the stuff Potter and his mates get up to?" he isn't just changing the subject, or trying to make two wrongs make a right. He knows that she is criticising Slytherins for a bit of spitefulness whilst Gryffindors are, quite literally, getting away with attempted murder. When she accuses his Slytherin friends of pulling a prank which is "evil", he knows that the Gryffindor boys' idea of a prank is to arrange to have somebody eaten alive by a monster, or infected with a disease which will ruin their life.
When Severus says he "won't let" Lily associate with the Marauders, he probably isn't being jealous or controlling: he knows that they are seriously dangerous, even psychopathic, and that she doesn't know and he isn't allowed to warn her. If he is being a little bossy in his desire to protect her, he is certainly being no more so than Harry is when he tries to order Ginny to sit out the battle in DH.
And, of course, he is right to be concerned. We later see James threaten to hex Lily, and even after they start dating James deceives her in order to go on hexing Severus behind her back. If they had lived, he would probably have deceived her in other ways too, and the fact that he accuses her of "making him" hex her, when all she is doing is trying to protect a friend from his aggression, suggests that he might very well have turned out to be a wife-beater. Whether or not James improved with age, at that age Severus had very good reason to think that James was a potential threat to Lily.
Time was to prove his concerns justified: her involvement with the Marauders was fatal. James may have shaped up a bit, and Sirius and Remus proved to be less of a threat to her than Severus had feared: but Peter killed her.
Note, incidentally, that it never seems to occur to Severus to lie to Lily. James will later lie to her to conceal his continued persecution of Severus, but it does not seem to occur to Severus to offer to give up the friends Lily doesn't like, and then go on seeing them in secret; or to promise anything he doesn't mean to deliver, just to keep her sweet.
Again, in the courtyard scene, Lily treats Severus rather badly. It sounds as if she has reason to be concerned about Avery and Mulciber, but she prefers to take the Marauders' word about the werewolf incident over Severus's and just assumes that he is "being ungrateful", and doesn't give him the slightest credence even though they are meant to be years'-long friends. And he repays her, as ever, with protectiveness and stammering adoration.
It also seems clear from the way she speaks ("I heard what happened the other night") that this is the first time Lily has discussed the Shrieking Shack incident with Severus, even though it happened at least a day and a half ago ("the other night", not "last night"), and she knows that he was in sufficient danger to require to be "saved". So, she knows her friend has had a horrible traumatic experience, she knows he's been in severe danger, and yet this is the first time she's spoken to him since it happened - she didn't seek him out to see if he was all right.
And now that she is speaking to him, for the first time since he was nearly killed, far from centring the conversation around his danger and his trauma she evidently sought him out to criticise him, since the scene opens with him saying "I thought we were supposed to be friends? Best friends?", which means she's said or done something which makes him doubt her friendship towards him. Contrast this with the way in which he will later throw away his political allegiance, his entire future and eventually his life because he thinks that Lily is in danger, even though they have long ceased to be "best friends", or friends at all.
In fact we see repeatedly, in their childhood interactions, in the courtyard scene and during and after the bullying incident, that even when Lily protests her friendship with Severus and makes at least some effort to protect him, she seems to have no care for, or no awareness off, any emotional suffering he may be going through. Either she is fond of him in a possessive way, as an item of her property, but has no care for him as a person; or she does care but she is somebody with a singular lack of empathy and emotional imagination.
In the bullying scene, Lily was slow to intervene on Severus's behalf. When she did, she didn't actually go to his aid even though he was choking - although that may have been because she was wary of being hexed by James if she took her eyes off him. According to JKR she already fancied James and was actually flirting a bit with him in that scene, over the top of her supposed best friend's distress and humiliation and despite the fact that James actually threatened her with violence. She does not even consider an offer which might have bought the Marauders off her friend's back for life (James said "go out with me" and he would spare Severus - he didn't say "go out with me more than once"), and she smirks when she sees Severus hung upside down.
In a brief moment of rage - and perhaps to protect himself from the consequences of being seen to be rescued by a Gryffindor girl, and perhaps to protect her from being hexed by James - Severus insults Lily and rejects her help in an offensive comment made to James, not to her. Lily's retaliation is ferocious, joining in in calling him "Snivellus" and jeering at his shabby clothes, which she knows very well that he is sensitive about and cannot help. Then she says that she doesn't want James to make Severus apologize - implying that she would accept a voluntary apology - and leaves him to his fate.
So Severus has suffered this horrible, public humiliation, including what is basically a minor form of sexual assault (exposing his genitals to a hostile, jeering crowd, or at least threatening to do so), yet all he can think about is putting things right with Lily. She has already taken her revenge on him by attacking and jeering at him in public, and she has indicated publicly that she wants his apology which she is now rejecting, yet he has no anger in the face of what we are told is her pitiless contempt: only meekness and apology and a willingness to humiliate himself further by making a public spectacle of himself in front of all the Gryffindors.
It seems clear from the way Lily speaks to Severus - "None of my friends can understand why I even talk to you" - "my friends", not "my other friends" - that Lily had already rejected him in her heart months if not years before, and was just looking for an excuse to get shot of him. And when she rejects him, and when she goes out with the bully who tormented him and still torments him, he still isn't angry with her. According to JKR, one of the main reasons he joined the Death Eaters was because he thought it might impress Lily.
[At first sight this doesn't seem very sensible, even for a teenage boy. But the Death Eaters in Vold War One were less racist than they would later become - JK has said, after all, that they actually tried to recruit Muggle-born Lily, so why would Severus think they hated all Muggle-borns? - and he thought that Lily only fancied James because he was "cool", and if he was cool too she might fancy him instead. Sev and the Evans girls come from a time and place - the north of England in the 1960s/70s - where domestic violence was common and some women saw violence in a man as proof of passion, and his own mother puts up with an angry and/or depressed man who appears to bully her. He knows that Lily fancies James even though James threatened her with violence ('Ah, Evans, don’t make me hex you'), and from Severus's perspective, at least, James is a bullying thug who has nothing to offer except his popularity. It's not unreasonable for him to think that Lily is prepared to put up with a lover who is a potential threat to her so long as he is cool enough, or is even turned on by threat, and he can certainly see that she is able and willing to fancy a bully. By this point Severus may know that Lily's sister too has taken up with a bully (albeit not a bully to her). All in all he had plenty of reason to think that Lily might be into violent, bullying men, so if he really did think Lily might be impressed by him becoming a Death Eater, that's not unreasonable. And if he did have any suspicion that the Death Eaters would oppress Muggle-borns, it would probably seem to him that he could protect Lily better from the inside.]
Lily tells him that he has made his choice, that he has chosen his creepy Death Eaterish friends over her: but in what we see, she never actually offers him a choice. She may have thought that the offer of a choice was implicit but teenage boys tend to be slow on the uptake, and need to have these things spelled out to them. At no point that we see did Lily ever say "Choose between them or me", and if she had done, he would probably have chosen her - insofar as that was possible. We don't know if Avery and Mulciber were in the same year as Severus but if they were, it would have been as vital to keep "in" with the potentially dangerous boys he shared a bedroom with as it was for Remus. [By the same token he couldn't have asked the Hat to put him in Gryffindor with Lily, because that would have meant sharing a dorm with James and Sirius who had already started persecuting him.]
But in any case Lily's behaviour suggests that she didn't really want Severus to choose her. He wasn't cool enough to hang out with her Gryffindor friends and, to be fair, the realisation that his feelings for her had become sexually-charged whilst hers for him had not probably made her very uncomfortable. My own theory about the dynamic between them is that Lily wanted her friends to be followers and her lovers to be masterful and offhand. Poor Severus didn't know how to make the transition: he wasn't mek enough to stay a follower, but when he tried to be masterful he only managed to sound whiny and controlling.
It's true there's something slightly obsessive about his unswerving devotion, even when she repeatedly kicks him in the teeth, but he certainly isn't a stalker in the usual sense of somebody who imagines a relationship where none exists, and then turns nasty when their imaginary affection isn't returned. Lily encouraged him to believe in their friendship, and it is she who turns nasty: apart from the one three-second burst of desperation and verbal rage, he never does, that we see. Coming from the sort of family he seems to, he probably doesn't see her nastiness towards him as unusual or as any reason for not loving her, or any reason why they shouldn't get together. He expects that couples will fight, and that the people he loves and who ought to love him will be nasty to him. By the same token, the fact that he is nasty to Lily doesn't mean he doesn't love her - he's just behaving in the way he's learned from his parents - and by extension the fact that he is often nasty to his students doesn't mean he doesn't care about their welfare.
And if he is more worshipper than friend, worship seems to be what she requires of him: since she rejects him utterly to punish him for one brief lapse from adoration.
It is striking that Sirius does not include Lily in the list of Severus's school-friends. Of course he may not want to say "He was a friend of your mum's" when he's blackening Severus to Harry, or he may really not know. If he knows who first and second year Severus was hanging around with because he was interested in Bellatrix and in his cousin Narcissa's boyfriend, rather than in Severus, or because his favourite cousin Andromeda was filling him on on the gossip, then he may never have known that Severus and Lily had been close friends (even though he saw them together on the train).
But that would mean that Lily cut Severus out so completely that she never told her new friends that she and Severus had been so close. That in turn reinforces the idea that her main objection to him was that he was embarrassingly uncool, because if she was talking to Sirius, of all people - Sirius whose brother became a Death Eater - and she had split with Severus because of his Death Eater wannabe friends, you would think it would be natural for her to say "I know what it's like".
Remus too seems to be unware of any reason why Snape might feel remorse for causing Lily's death. So it really looks as if, despite supposedly being "best friends", Severus and Lily were not seen around together much even before their quarrel, and after it she edited him out of her life, and did not tell her new friends that they had ever been very close.
It also shows that Severus did not behave in a stalkerish manner. He continued to "carry a torch" for Lily and (interview canon) continued to hope that if he impressed her enough he might win her back, but he accepted her rejection and did not pursue her in any obvious way. If he had done, surely Remus and Sirius would have been at least vaguely aware of it.
When Severus finds that he has endangered Lily, even though she has rejected him, even though she has married his tormentor, he throws over his allegiance to Voldemort and risks everything to save her - putting himself in extreme danger from both sides, in an era when both sides are torturers and killers.
Dumbledore calls him disgusting because he only asked Tom to spare Lily, not the whole family, and because it's Lily he is most concerned about. But really, it's natural for a not-especially-mature lad of twenty to be more concerned about the fate of a woman he is in love with than about an enemy or an infant he has never seen. And despite Dumbledore's comments, he isn't sacrificing Harry and James when he asks Tom to spare Lily: they're doomed anyway, and there's no way he can save them, other than by doing as he has done and defecting. What excuse could he give Tom for wanting to spare a child whom Tom perceives as a threat, and a man Tom probably knows he has good reason to hate? If he tried to get Tom to spare all of them he would lose all of them, and himself - or at least Tom's trust in him - to no good end. Whereas he does have a chance of saving Lily, and Tom does in fact make a half-hearted attempt to honour his request.
If he had not, of course - if Snape hadn't asked for Lily's life, and Tom hadn't offered it to her - there would have been no willing sacrifice and no blood protection and no rebounded curse. Tom would simply have killed Harry, and taken control of wizarding Britain.
At no point in the conversation between Severus and Dumbledore does Severus actually agree that he had offered to trade Harry and James for Lily - and it's difficult to see in what sense he could possibly have done so - or even say that he only cared about Lily. He seems tongue-tied and confused by Dumbledore's accusation, as he was by Lily's, and all he actually agrees to in Dumbledore's tirade is that he asked Voldemort to spare Lily.
And Dumbledore sacrificed any claim to the moral high ground when Severus asked him to save all the Potters, then, and Dumbledore replied "And what will you give me in return?" Severus held to his side of the bargain - that he would do anything - but Dumbledore was lax in his, since he borrowed the Cloak which "hides from Death" from James and failed to return it, even when he knew the Potters were in extreme danger. Severus did indeed, as Dumbledore said, put his trust in the wrong person.
[It is irrelevant whether the Cloak would have saved them, in the event. Dumbledore couldn't know in advance whether it would save them or not but he must have known there was a good chance that it might, yet he still hung on to it.]
In any case, if we criticize twenty-year-old Snape for caring more about Lily than about Harry and James, what are we to think about seventeen-year-old Harry? After the trio have fled from Bill and Fleur's wedding, and Arthur has sent his Patronus to reassure them that the Weasleys are safe, Ron is overcome by emotion and Hermione joins him, whispering "They're all right, they're all right!" as if it truly matters to her. Harry understands Ron's reaction, but his own reaction is described thus:
The Weasleys are friends he has known for years; they have welcomed him into their family and Molly in particular has loved him like one of her own sons (if anything, more than she seems to love her own sons). They are not, as James and Harry were to Severus, a bitter enemy and a complete stranger. Yet in order to share Ron's concern about them, Harry has to think of the girl he is in love with: he does not seem to feel any great personal concern for the safety of Arthur and Molly and the rest. He sympathizes with Ron's worry about them, but he does not share it, as Hermione does.
And yes, he has some excuse because he was distracted by the pain in his head; but so was Severus distracted by the twin terrors of Voldemort and Azkaban. As is often the case, Harry and Severus are shown to be quite alike in many ways, and if we forgive Harry's exclusive fixation on the girl he loves, so we should forgive Severus's.
When he learns of Lily's death Snape reacts with true grief, not just guilt: nobody howls in agony out of guilt, unless they are some kind of self-dramatising religious fanatic. Yet he does not rage at Dumbledore, who has failed to keep his promise, and who treats him with great cruelty, reminding him of Lily's eyes when he is in the jaws of his misery, when it would have been enough to say "There is still something which you can do for her." Just as he never blamed Lily for ill-treating him, so he never blames Dumbledore, until the point where he learns that Dumbledore has used him to set Harry up to die.
Actually, when we see his interactions with Lily and with Dumbledore, Snape seems remarkably free from resentment. This suggests that his sniping at Sirius is not so much because he bears him a grudge but because of the ferocious competitiveness which landed him in Slytherin in the first place. He doesn't want to hurt Sirius: he just wants to prove he's won. And his tension about Harry is partly because the fact that Harry has Lily's eyes in James's face is a constant reminder that James bested him in the battle for Lily's affections.
We know that Snape kept the second page of Lily's letter to Sirius, and left the first page, which Harry later found crumpled, but we are not actually shown whether Snape crumpled it deliberately. He could have done; or Kreacher could have done; or it could have been crumpled when Snape found it; or Snape could have done it accidentally by clutching it too hard. Psychologically, the most likely person to have crumpled it is probably Sirius, when he re-read Lily's comment about Wormy seeming a bit down, but if the letter has spent a year or more slotted into Bathilda's book - as it seems to have done - that would probably have flattened it again.
Either way, Snape seems callous or obsessive when he tears the photograph apart so he can take only Lily with him, and takes only the page of her letter to Sirius which has her signature on it. But how did the letter get to Grimmauld Place - since Sirius wasn't living there when Lily wrote it - and how did Snape know the letter even existed?
The most likely explanation of how the letter got to Grimmauld Place is that it was with Sirius's effects which were returned to his family on his arrest. Snape might surmise that: but unless he and Lily had actually become friends again before her death, or Sirius had taunted him with his friendship with her, he couldn't know for sure that Lily had written to Sirius, or that Sirius had kept the letter. It seems unlikely he would have taken the risk of searching Grimmauld Place for a letter from Lily just on spec - or that it would just happen to be a letter which pointed Harry down the road to Bathilda Bagshot.
We can assume, then, that Dumbledore knew the letter was there, and sent Snape to get it. We are never told why the Potters refused to have Dumbledore as their Secret Keeper, but considering this letter it seems likely that it was because they had found out about his connection with Grindelwald; and Sirius may well have admitted having such a letter when he argued with Dumbledore, either before or after his time in Azkaban. Albus's repeated undermining of Sirius, his cutting him out of any sort of decision-making loop to do with his own godson, may well have been because Sirius had something on him and he wanted to weaken his influence.
So, Albus sends Snape to Grimmauld Place to retrieve the letter, to conceal his connection with Grindelwald from Harry. Snape takes the part which refers to Grindelwald, but he leaves the rest: perhaps because Dumbledore has told him to, in order to steer Harry towards Bathilda. Bathilda would then be very likely to tell Harry about Grindelwald: but perhaps Albus does want Harry to know about that, in order to point him towards the Hallows, but he would rather Harry hears the full story from somebody who was fond of Gellert, rather than be shocked by a casual out-of-context revelation.
Or perhaps Albus wanted Snape to retrieve the whole letter, but he chose only to take the part dealing with Grindelwald, and left the rest - so Harry could see what Albus had done. Either way, it seems likely that the rage and grief which left Snape weeping and crumpling the letter in fury (if he did) was not only love of Lily, or resentment of Sirius or of the married happiness which Lily described, but the revelation that all the while Dumbledore had been supposed to be keeping the Potters safe, he had been hanging on to their Invisibility Cloak for himself, even when they were in the greatest danger. Perhaps, too, he was affected by the realization that it was Dumbledore's link with Grindelwald which must have led Lily to put her life in Peter's sweaty hands instead.
Tearing Lily out of a family photograph seems harsh: but really, it's completely natural that Snape would want a photograph of the girl he loved, and completely natural that he wouldn't want one of the bully who made his schooldays a living hell. And apart from his general dislike of Harry, Harry is a very sore point by now and a source of misery and guilt, because this is after he has found out that (as he thinks) he and Dumbledore have raised the boy for sacrifice. It's understandable that seeing a picture of Lily with her son would distress him.
Nor is the rough, rather destructive way he chucks Sirius's papers about evidence of any character-fault. Harry loved Sirius, but he throws his things about equally casually in an attempt to find more of Lily's letter.
One might ask why, if Snape loves Lily and protects her son for her sake, he isn't also nicer to the boy for her sake. But from what we see of his family life, he has no reason to expect that parents will be particularly kind to their children, or care whether other people are. His father seems to be perpetually ill-tempered. His mother sends him out in weird clothes which make him a laughing stock, and at King's Cross we see him stand near her with his shoulders hunched, as if he expects her to shout at him or hit him. The Evanses probably weren't good rôle models either: Petunia doesn't seem like the product of a happy home, and if she is to be believed they played favourites. Nor - judging from the way she treats him, and her sneering at the present Petunia gave her, and the enmity with which Petunia still regards her twenty years later - does he have much reason to think that Lily would treat her supposed loved-ones much better than his parents did.
Harry says Snape's Patronus is the same as Lily's, although as Harry has never seen Lily's Patronus one wonders how he knows. Snape's silver doe may possibly represent Lily to him, rather than being the same as her Patronus. It seems mentally healthier if it really is her Patronus, though. Otherwise one would have to think that Snape sees her as a doe because she is the mate of the stag, James, which would be self-lacerating - and confusing, because he didn't even know James was a stag Animagus until the end of Harry's third year. And Dumbledore recognizes the doe - so probably Harry is right and it's Lily's Patronus. If there is a connection between that and Prongs, probably James saw Lily's Patronus in class and that led him to take that particular Animagus form.
[There is an anomaly here, though. Stags mate with hinds; does mate with bucks. James got the wrong species.]
At any rate, the Patronus is supposed to be made out of something happy, so it's unlikely that even Snape could have made a Patronus out of guilt. Whether his Patronus is Lily's or represents Lily, it shows that he still loves her years after her death, and sees her as his star and safety. It surely represents a kind of beauty in him, his love and loyalty and his desire for what is beautiful, as well as the beauty of the person he loves. And the fact that he is able to generate a Patronus - and such a Patronus, clear and sharp and stable, able to remain firm and to walk around for long periods almost like a real animal - from the memory of someone who in fact rejected him suggests that his love of Lily was selfless and self-sufficient. He loved her, not what she could do for him, or perhaps he loved being in love: either way, the strength and warmth of his feeling was not dependent on her loving him back.
Nevertheless, it is not the case that he only ever cared about Lily and about nothing else. He promised Dumbledore "Anything" in return for keeping the Potters safe, but Dumbledore failed in his part of the bargain. Nevertheless Snape continues to serve Dumbledore in all things, not just to protect Harry, which could probably have been better done by spiriting the boy abroad. We see him protect other people whose safety does not bear on Harry's safety. And he continues to fight for the Order, to risk and ultimately lose himself and to defend the school, even when he knows that doing so may mean Harry's death. Some of that could be his desire for revenge on Lily's murderer: but there is no way that risking discovery by giving Ginny, Neville and Luna a reward-detention, for example, directly serves any interest of Lily's.
As Silvialaura on Loose Canon put it: "He did chose to stay, fight and screw up his life after Lily died, instead to mourn her in a nice resort in the Caribbeans... So at one point he must have changed from 'I want Lily' to 'I want Lily safe even if she's not mine' to 'I want to work for the same things Lily wanted' and eventually, 'I want to work for things that are right even if Lily may not agree'."
In his head, it may still be Lily he is fighting for: but really he has translated her into some sort of goddess-figure, and he fights for the good which Lily represents for him, and which really has more to do with his own virtue than hers. Nor is this pathological or even particularly bizarre: just very old-fashioned. This idealization and abstraction of a beautiful, loved girl is very much the sort of attitude early Mediaeval knights were encouraged to develop towards the lady whose favour they wore.
Snape undoubtedly has an abrasive teaching style; and we know this is counterproductive in some cases. We are told that both Harry and Neville are more relaxed during their Potions OWL practical than they are in class, because Snape isn't there, and Harry at least does better as a result. Harry also performs better in class when Snape decides to ignore him after the Pensieve incident, so Snape's tendency to hover is counterproductive in at least some cases. Not that this affects Harry's or Neville's results in the long term: they do perform well in the OWL practical, and it doesn't really matter that they might have performed better in the practicals in class too if Snape had been less of a nagger, because the practicals in class don't contribute to their final marks.
There seems to be no teacher-training in the wizarding world, so Snape is making it up as he goes along, and we see in DH that he receives no managerial support. He may be being a little unfair to Harry when he rants about him to Dumbledore, but it's certainly not true that no other teacher has a problem with Harry: he is equally lazy and inattentive, if not quite as cheeky, to Binns as he is to Snape, and will later be even worse to Trelawney. And wherever the fault lay, there clearly was a problem between Snape and Harry, which needed to be addressed: yet when Snape tried to discuss it with his manager, Dumbledore didn't even do him the courtesy of looking up from his magazine.
For much of the time that we know him Snape is in great danger from Voldemort, not to mention working about an eighty-six-hour week, and must be very tired and stressed. And he probably has to exist in a permanent bad temper, and not try to modify his own anger, because he needs to present a convincing front of rage and bitterness when Tom reads his mind. It's not surprizing, then, that he is often sour and harsh in the classroom. Overall, however, his methods do seem to work. He tells Harry's year that he has a high pass-rate and expects all of them, even the worst students, to pass at OWL or suffer his wrath, and even Umbridge, who is trying to find fault, comments that his fifth-year students are quite advanced for their age.
Arguably, he has to pay especially close attention to both Neville and Harry because he knows Neville may cause a dangerous explosion by accident, and suspects Harry of having caused a dangerous explosion deliberately in second year. And being very nervous and tense he can't stop himself from picking at them as he watches them.
Snape certainly isn't the only teacher to use sarcasm. It was Flitwick who set a student the line "I am a wizard, not a baboon brandishing a stick." And neither of them is as sarcastic to their students as McGonagall is to Trelawney at the Christmas dinner in PoA.
At twenty-one, Snape was teaching fifth, sixth and seventh year students who had actually been fellow students of his, and knew him as Snivellus, the bullies' favourite victim. His first seventh year class had been first years when he was forced to eat soap, hung up by the heels and (probably) publicly stripped, and some of them may well have witnessed it: they will almost certainly have heard about it. It must have been nightmarish, and it's perhaps not surprising that he got into a bad habit of ruling by fear.
It's not clear whether Snape is abrasive and overbearing in class because he is taking his temper out on the students, or just because he still feels surrounded by enemies, and lashes out. Certainly any Potions class does need to be monitored closely, since the children are dealing with dangerous substances and an accident could kill - and not just the person closest to the cauldron. And teaching is hideously stressful - like standing up on stage to sing and having the audience continue to talk amongst themselves. A friend of mine quit teaching after she lost her rag and picked an annoying pupil bodily off the floor by his hair. At that point she decided she had to change careers, because if she stayed any longer she might actually murder one of the little brutes.
Part of Snape's problem is that he doesn't seem to know whether he's a teacher or a student. He dresses in black robes like the students; he sleeps downstairs, probably not far from the Slytherin dormitories where he slept as a child. One minute he acts like a kid - calling Hermione a know-it-all, which we're told the children all do - but if the kids respond in kind he gets touchy and pulls rank.
The messy detentions he sometimes sets - e.g. cleaning bedpans without magic - also seem rather childish. But considering his comment about "foolish wand-waving", there may be a serious intent to teach the value of work done with the hands. Plus, of course, some of the tasks he sets - sorting flobberworms and so on - are things that he'd probably have to do himself, if he couldn't find a student to offload them onto.
That we know of, he is the youngest permanent faculty member by far, living and working where he's lived since he was eleven, with colleagues many of whom taught him when he was eleven, and who probably gave him detention not long ago. Dumbledore, at least, seems to veer between treating him as a colleague and treating him as a child, so it's natural that he himself sometimes acts a bit confused about it.
I am told incidentally that American readers may think that Snape is being unreasonable when he gets irritated with Hermione for being a know-it-all, and comments unfavourably on the fact that she quotes the textbook about non-verbal magic. But students in Britain are supposed to demonstrate personal understanding and input, and any good British teacher would be disappointed by a supposedly bright pupil who just quoted back what they'd read.
Snape's insistence on Harry calling him "sir" seems stuffy, but he doesn't object, in HBP, when Lavender or Hermione don't call him "sir". During the Occlumency lessons he gradually stops insisting on Harry calling him "sir", when Harry is talking to him as an Order member and being fairly friendly.
It seems likely, therefore, that he insists on Harry calling him "sir" as a mark of respect because he knows that when Harry omits to do so, it's usually because Harry doesn't respect him. Similarly, Dumbledore insists on young Tom calling him "sir" or "Professor", although he is much less stuffy with Harry and co.; and even Hagrid roars "I'm a teacher! A teacher, Potter!" when he feels Harry is being disrespectful.
Yet, Snape is remarkably lenient over that "You don't have to call me 'sir'" stunt. If someone tried that on McGonagall they'd probably get a lot worse than one detention. Either Snape is really quite soft, or he's being lenient because of Harry's recent bereavement, or he's privately thinking "Nice line - wish I'd thought of it".
As a teacher, Snape occasionally makes mistakes and can be inconsistent - taking a point off Harry in their first lesson for not helping Neville with his potion, then later taking them from Hermione for helping him. [It's true that in the first lesson they were working in teams, and later they were working solo: but Neville wasn't on Harry and Ron's team.] He was wrong in PoA to say that Kappas mainly live in Mongolia (they're Japanese), and he causes confusion in HBP when he asks Harry how you tell the difference between an Inferius and a ghost, and then gets angry when Harry very reasonably replies that one is transparent and the other isn't. It seems clear that Snape meant "What is the difference between...?" rather than "How do you tell the difference between...?" and hasn't realized that he misspoke. But these inconsistencies may be due to being fuzzy-tired, rather than capricious.
In common with all the teachers who teach classes which are compulsory from first year to OWL, he teaches twenty-seven hours of classes every week, comprising two single (45 minutes) and two double (1½ hour) periods per week for each of years one to five, and one single and one double class for each of years six and seven. That's twenty-four classes, each of which must require some preparation - if we say a quarter of an hour each, that's six hours a week of preparation.
Then, he is teaching all the students in years one to five, and maybe a fifth of those in years six and seven, and in an average school year there should be around ninety-five pupils (see Population and Pupils), so he is teaching something over five hundred students. Even if he only sets each student one essay a fortnight, and only spends ten minutes reading each essay, that's forty-two hours of marking per week.
In common with the other heads of house, he also has his administrative and pastoral duties as head of Slytherin, which must take at least another five hours a week. In addition, like McGonagall he also patrols for at least another couple of hours a week, and on top of that he has stocktaking of his ingredients, and probably brewing for the hospital wing - probably at least another four hours a week.
That all takes us up to eighty-six hours a week, but on top of that he has his duties for the Order, and whatever duties he pretends to perform for Voldemort (from the end of GoF, and he probably did some keeping of an eye on the former Death Eaters before that), plus we know he teaches at least some remedial classes. Only McGonagall - who has her administrative duties as Deputy Head in place of Snape's pseudo-service to Voldemort - has an equally gruelling timetable.
Of course, the staff live in and don't have to waste hours commuting (and they get sixteen weeks' holiday a year), and as kittyperry pointed out they don't have to do any of their own housework, but even so it's a killer schedule, and Snape's involves actual physical danger, and hence extreme stress. It's not surprizing if he occasionally misspeaks or tells somebody to do the opposite of what he told them last week: and the added imposition of having to brew Wolfsbane, which we are told is very complex, must have been exhausting, even if it was an interesting challenge.
Nevertheless, although Snape is tired and scratchy he takes his duties seriously. He speaks of his subjects, both Potions and DADA, with passion. He tells the students where they go wrong, amongst the sniping, and he has an encyclopaedic knowledge of potions and seems always to be able to spot what mistake they've made to cause every possible change of colour or consistency. He comments on essays, showing he has read them properly, and he seems to mark reasonably fairly whether or not he likes the student. It seems clear from the hints she drops that he marked Hermione "Exceeds Expectations" in the mock-test prior to OWLs, and after the Pensieve incident, during the lesson in which Harry's potion-sample gets broken (of which more anon), Harry expects that Snape will give him an E for a good potion. Even though he knows Snape is furiously angry, he doesn't expect that prejudice will affect his marking.
We know Snape does teach at least some remedial classes as well, because he comments to Draco about Crabbe and Goyle needing to work harder to pass their DADA OWL resits, and because presenting Harry's Occlumency training as remedial Potions lessons seemed to him to be a believable cover-story.
Snape doesn't explain Occlumency very well to Harry - but putting psychic phenomena into words is like trying to describe yellow, especially if it just comes naturally to him. This may well be the first time Snape has had to explain, or teach, Occlumency to another person.
And despite his killer schedule, he finds time to patrol. He probably does get spiteful pleasure out of catching people out, but in a vast, rambling building where there are so many dangers (not just basilisks and Cerberuses but trick steps you could snap your leg in), and so many bullies, making sure that everybody gets back to their dorms safely is sensible and responsible.
Some American readers apparently think that Snape's harsh, critical attitude to the students' work is actually damaging their prospects, that it reduces their grades, but apart from the risk of putting them off the subject through discouragement it does them no harm at all. At Hogwarts, as at nearly all British schools when JK (and I) was at school, your final results depend solely on how well you do in the OWL and NEWT exams. Not only is this what you would expect, given that Hogwarts is loosely based on Rowling's own school, but we know that this is so because Trelawney tells her class to pay close attention to a particular piece of course-work because it might come up in their OWLs. I.e., the course-work is not important to their final results in itself, but only because it might help them do better in the fifth-year exam.
Hence, even when Snape gives Harry a zero it has no impact on Harry's final marks whatsoever, and in fact by training the students to strive hard to get even passable marks in class, Snape probably improves their chances of getting a really good mark in the exams that actually count. He does tell them that he expects every one of them to pass Potions OWL.
Snape's especially harsh criticism of Neville is counterproductive, since it makes the boy more jittery, but it is all relevant to his performance in class: he seldom actually punishes him (one detention for melting his sixth cauldron in fourth year, and a few points taken for fighting in fifth year), and never attacks him for his brain-damaged parents or his general vagueness. He perhaps thinks Neville will work harder to prove him wrong out of spite, because that's what he'd do. And indeed, since he apparently comes from quite a dysfunctional family, his constant nagging of Neville (and by implication of Harry) may be because he is genuinely concerned for the boy's safety, and in his experience constant nagging is how you show that you care.
If it sounds far-fetched that he might actually be concerned for Neville, bear in mind that at the end of OotP he risks his job - by antagonising Umbridge further when he is already on probation - in order to stop Crabbe half-throttling Neville. In DH he risks his position as quadruple agent, his life, and with it the safety of the school and the outcome of the war against Voldemort, in order to circumvent the Carrows and give Ginny, Luna and Neville a "punishment" which is actually a reward.
He presumably doesn't know that Neville's family used to put him in actual danger of death in an attempt to squeeze more magic out of him. This is probably why Snape is Neville's Boggart - not because Snape is so dreadful that he is the main fear-trigger to a boy whose parents were tortured into insanity, but because in Neville's experience if you're useless at magic people try to kill you, and your family would rather see you dead than a Squib - so Snape's criticism represents threat-of-death and rejection-by-family.
It's also entirely possible that Neville - whose parents were Aurors and whose grandmother is powerful and well-connected - is scared of Snape because he knows Snape is an ex Death Eater. Either way, Snape's sinister, Gothy manner won't help Neville's nerves - but Snape is a posy Goth type and he probably doesn't feel inclined to change his entire style to suit one student.
There seems to be no teacher-training in the wizarding world, and no apparent awareness of learning difficulties. Snape probably teaches as he was taught. His behaviour to Neville is not really much worse than McGonagall's, when she severely punished a boy with known memory problems for having a bad memory. He wasn't even careless with his password-list: he kept it inside Gryffindor Tower where only someone who had a right to know the passwords should have been able to see it. He could hardly expect Crookshanks to burgle the dorm. Yet she gave him detention, banned him from Hogsmeade apparently forever, and made him repeatedly wait in the corridor, with a supposed mass-murderer possibly loose in the school, until a classmate let him into the common room - which we're told was specifically intended as punishment, not a security measure. It's small wonder if Neville still believes that if he's bad at magic he'll be put in danger of his life.
McGonagall admits she was "often rather sharp with" Peter Pettigrew, to an extent which makes her tear-up as she speaks of how she regrets her harshness, believing Peter to have died a martyr's death.
Remus says that James and Sirius were "the cleverest students in the school", and even though he's probably a biased source, McGonagall also calls them "exceptionally bright". So it appears from what she says that she was "rather sharp" with Peter just because he wasn't in the same league as his brilliant friends. If Slytherin and Gryffindor were paired in Transfiguration in those days Snape will have witnessed this, and whether he did or not it's unlikely that Peter was the only slow student she was harsh to, since we see her still being hard on Neville.
Snape probably learned his teaching style from her, except that he's rattier and not so smooth: being over thirty years younger and less experienced, and much more stressed-out. And the teaching style he learned from her included "Be hard on slow students" - but at least Snape never made Neville humble himself in front of his classmates, nor does he punish him for his vagueness - just nags him. He also protects him - from blowing himself up, and later from being throttled by Crabbe, and later still from being tortured by the Carrows.
[Why is he not equally hard on Crabbe and Goyle? The usual assumption is "because they're Slytherins" but it may in fact be because they are genuinely slow, and he knows them to be working to the limit of what little ability they have. We do see him give them both detention in HBP when he feels that they are being lazy and failing to keep up with their remedial DADA work. Neville is not without ability and in fact Pomona Sprout probably boasts in the staffroom about how brilliant he is, with the result that Snape feels the boy isn't pulling his weight. And he's right, of course, but Neville isn't failing deliberately and nagging him only makes the problem worse, by making him more jittery and confused.]
Snape in any case has good reason to be tense around Neville, which will make him more sensitive to the boy's failings, and less patient with them. He knows that if Neville causes a serious explosion he himself will probably be caught in the blast. He probably knows that either Harry or Neville is the boy prophesied to bring Voldemort down, and that their failures make Tom's victory and his own death more likely - and he may know or suspect that it was because he relayed part of the prophecy to Voldemort that the Longbottoms were targeted, as well as the Potters, adding guilt to an already uneasy mix.
He may also have another, darker reason to be uneasy around Neville. We know Snape was investigated by the Wizengamot at a time when the Aurors were authorized to torture suspects - and that Neville's parents were Aurors at that time. At one point we are told that both Neville's parents were Aurors, at another that only Frank was, which probably means Alice was on extended maternity leave during the last years of the war: or perhaps that she had switched to working in Records, which would explain why Bellatrix and co. thought the Longbottoms might know where Voldemort had gone. But there's a good chance that Frank at least was a torturer, whether or not he tortured Snape himself. He was certainly a colleague of torturers - something like a KGB man.
Only three times does Snape's behaviour towards Neville seem really extreme. Once is when he tests a potion on Trevor. But bringing a poorly-controlled pet into a class full of fires and dangerous chemicals is very inappropriate, and callousness towards non-human animals seems to be the norm at Hogwarts (e.g. turning hedgehogs into pincushions and then sticking pins in them when some of them are still clearly aware and in pain - and let it not be forgotten that according to Fabulous Beasts Fred Weasley beat Ron's pet Puffskein to death for fun).
We also see, from the Swelling Solution incident in CoS, that Snape keeps antidotes handy for whatever is being brewed, so if Trevor had been poisoned he could probably have reversed it; and there may well have been nothing lethal in the ingredients anyway.
At the duelling club in CoS, Snape tells Lockhart that it's a bad idea to use Neville and Justin as a demonstration team, because 'Longbottom causes devastation with the simplest spells, we'll be sending what's left of Finch-Fletchley up to the hospital wing in a matchbox.' This is a backhanded compliment of sorts: he's saying that Neville has immense power, even if very badly controlled.
It's still a very rude thing to say, especially in front of the class, but at the same time it's probably a genuine worry - Neville really might do something dangerous to Justin, and embarrass himself in front of the class as well - and there's no opportunity to speak to Lockhart in private about it. Even if Snape could stand the idea of speaking to Lockhart in private about anything. He could probably have found a more tactful way to put it - but Snape is nothing if not tactless, and the presence of Lockhart would automatically put him in a foul mood.
The other occasion is when he criticizes Neville to Lupin in a sneering way in front of the DADA class. This is certainly unkind, but again the advice is sound: Neville is a poor performer who needs close supervision in a subject which may be actively dangerous. Snape may even be trying to put Lupin off from involving Neville in the Boggart-session because he is afraid that Neville's Boggart will be his parents screaming under torture, which he can't say openly to Lupin in front of the class and has no opportunity to say to him in private.
[You have to wonder what on earth Lupin was playing at anyway, making the students reveal their deepest fears to each other, and involving Neville. Lupin is an Order member, he knows what happened to the Longbottoms and probably knows Neville doesn't like to talk about it, so he must have known there was a good chance the Boggart would force Neville's secret into the open against his will. It could have revealed all manner of things people wanted to keep private - sexual abuse, criminal behaviour by themselves or their loved ones, things which could easily lay students open to persecution or even drive them into suicide if revealed publicly. None of which seems to have occurred to him, or worried him if it did. This tends to support my opinion that Remus is basically a sometimes-man-shaped canine with a very high IQ, rather than a human who sometimes turns into a wolf. He doesn't get those kind of human sensitivites and embarrassments.]
There are also reasons why Snape may have been in an unusually foul mood. We know that he was nearly mauled by Lupin when he was a schoolboy, and that he probably witnessed Lupin's transformation before James intervened. We then see, in PoA, that Snape is still very scared of Lupin. He watches him neurotically at dinner; he urges him to take extra Wolfsbane (just to make sure he won't have to see that transformation again); and when he leaves after giving him the Wolfsbane he backs out of the room without taking his eyes off him. Lupin may well be Snape's Boggart.
And there is Snape, sitting alone in the staff room with an odd look on his face (glittering eyes and sneer seemingly already in place) and a Boggart in the cupboard, probably thinking about Lupin and whether he can face the Boggart, and then Lupin walks in to conduct a Boggart-facing session and Snape doesn't want to witness it. It's perhaps not surprising if he's very tense - and being Snape, when he's tense he lashes out at the nearest target.
In any case, once again Severus behaves no worse than McGonagall, whom Rowling considers to be "very good". McGonagall overseas classes in which experimental animals are treated very cruelly, and even aside from the business of making Neville wait for his classmates to let him into the common-room in PoA, she also denigrates him in front of a class - just as Snape does.
And both Snape and McGonagall nevertheless indicate that they expect Neville to pass his OWLs although Snape, being Snape, does so with a poorer grace.
'I see no reason why everybody in this class should not achieve an OWL in Transfiguration as long as they put in the work.' Neville made a sad little disbelieving noise. 'Yes, you too, Longbottom,' said Professor McGonagall. 'There's nothing wrong with your work except lack of confidence.' [OotP ch.#13 p.232]
Some readers may think Snape was being especially cruel when he gave Neville a detention which involved disembowelling a barrelful of (presumably already dead, since they came in a barrel) horned toads, since Neville has a pet toad. This is a difficult one because it's a case where probable authorial intent clashes with what's on the page. It seems likely that JKR herself did intend Snape to be being malicious or callous here, because she refers to Hermione helping to clean what Harry at least thinks are "toad guts" (originally "frog guts", so her mind was dwelling on amphibians) from Neville's hands. But the text clearly says "horned toads" and horned toads are a type of lizard, extravagantly covered in spikes and resembling toads only in having a tubby body and a wide mouth.
Snape's very jumpy, snarly, hyper-vigilant manner suggests that he is a survivor of serious physical abuse. That may just mean the combination of severe bullying at school and trying not to get Cruciated by Tom - but if he was actually battered as a child, then part of his problem as a teacher, insofar as he has one, is probably that his mental goalposts have been shifted. If his concept of "treating children badly" is "thrashing them with a belt like my dad did", it may not occur to him that verbal hectoring can also be stressful and damaging to a nervy boy like Neville.
We must also remember that extreme corporal punishment was practised at Hogwarts well into Dumbledore's watch (we're told that Arthur Weasley was scarred for life by his punishment for being out after curfew with Molly), and may well have still been in place when Snape himself was a schoolboy. So again, he will be predisposed to think that snapping and snarling is gentle treatment.
Harry feels that Snape becomes even more harsh in his attitude to Neville, after the Boggart scene. On the one hand, this seems cruel when he has just learned how afraid of him Neville is. On the other hand, it has just been demonstrated that Neville can perform well in class with sufficient incentive, so Snape may now feel (wrongly but understandably) that Neville's failures in his class are due to laziness, or that the best way to motivate Neville is to scare him, or that if he pushes him hard enough he'll be able to make him perform. And he's actually right about that last one - so far as we know he does eventually manage to bully Neville into an "Acceptable" OWL, although with a great deal of stress on both sides which could have been avoided if he'd coaxed instead of hectored.
In any case, as a teenager Snape suffered at least one minor sexual assault by the Marauders - being hung upside-down and stripped in public, or even threatened with being stripped, would definitely count as extreme sexual harrassment - and there is a hint that his relationship with Lucius at school might have been sexual: if so it would have to be at least borderline abusive, because of the great age-gap.
It's very common, in people who have been abused when young, that if they are attacked again as adults they react more catastrophically badly than a person who had never been abused would do. The reason is that the fresh assault is not only horrible in itself, it causes them to have a massive flashback to the mental state they were in during the original abuse, and it makes them feel as if all the work that they have done over the years to recover from that abuse has been undone or was pointless. They feel they are a weak, helpless person who can never get away from the abuse, it's going to go on forever.
[This, of course, is probably what Snape makes Neville feel about flashbacks of Uncle Algie, too - but Snape doesn't know about Uncle Algie.]
So the quasi-sexual and very public humiliation of having a projected image of himself dressed up in an old woman's clothes and mocked would bring back a raft of horrible, burning feelings which would not endear either Neville or Lupin to him.
Lupin is perhaps the better teacher: but in time of war, which would you prefer - the sour, overbearing master who will risk his life to save you, or the sweet-tempered, patient one who will risk your life to save himself? And Lupin's own life wasn't even in danger in PoA. He believed that Sirius was a mass-murderer who was out to kill Harry, yet he kept the information about the secret tunnels and about Sirius being an Animagus secret apparently just to save face, or in pursuit of some obscure private agenda. Snape, on the other hand, is always risking himself for Harry specifically, and for the children in general.
When Harry was a baby, Snape risked being killed by Voldemort, in an attempt to save Lily, at least - despite presumably believing the story that Regulus had been executed for defecting. He then continued to subject himself to extreme danger, in order to spy for the Order, protect Lily and perhaps atone for having joined the Death Eaters.
Dumbledore accuses him of only being interested in saving Lily, and not caring about Harry or James, or even of being prepared to sacrifice them for Lily: but he seems to be just assuming this without evidence. We can tell how unreasonable he is being, in fact, because he suggests that Snape may have offered Tom Harry in exchange for Lily's life. Snape didn't know that the prophecy had anything to do with either Lily or Harry until after he had relayed it, and once he had done so he had no power to "exchange" Harry for anything - unless Dumbledore is suggesting that he might reveal the Potters' whereabouts, an idea for which he seems to have no evidence whatsoever.
It would be quite natural if Snape had only asked Tom to spare Lily, because there was no conceivable excuse he could give him for wanting him to spare Harry or James, but we never find out if Dumbledore is right even about that - since he accuses Snape and then won't let him speak. It's also quite natural that he thinks first of his childhood friend, rather than of a bully who persecuted him and a baby he's never met. Later on he shows protective concern for Harry, if only for Lily's sake, but he also protects the school and the children generally.
In Harry's first year Snape headed off, alone, to protect the Philosopher's Stone while everybody else was chasing the troll. He let his colleagues think he had insisted on refereeing a Quidditch match in order to cheat, and made himself very unpopular with them - submitting himself to suffering in the staff room the same sort of isolation and scorn which Harry suffered over his entry into the Triwizard Tournament - in order to protect Harry, whom he doesn't even like.
In Harry's third year, he went alone down a long tunnel in the dark, to the place where he had nearly been murdered as a boy, to face the two people who had nearly murdered him - one of whom he sincerely believed to be both a mass-murderer and a high-ranking Death Eater, and the other of whom he knew to be a werewolf on the point of transformation, and of whom he was terrified. Why not call a Dementor to help? Why not wait by the tunnel-mouth for Sirius and Remus to come out? He knew they'd have to come back the way they went in: he'd been down that tunnel before, so he knew it had no side-exits and it's common knowledge that the Shack itself is sealed.
The only thing which required immediate intervention, and which made it unacceptable to bring a Dementor, was the presence of the children. We know Snape sprinted the whole way, because when he saw Lupin on the Map he was almost at the edge of the school grounds and running flat-out, and yet Snape got to the Shack only about five minutes after Lupin did: even though Lupin knew the way far better than he did, and the tunnel was so low in places that a short thirteen-year-old had to bend almost double.
It's true he didn't see the children on the Map, as they had already passed the boundary, but he expected Lupin was going to meet Black, he believed Black was after Harry - his first thought would surely have been to check the Map to make sure Harry was where he should be, and find out that he wasn't. As the Order's spy he probably knew James had an Invisibility Cloak, Albus had probably told him he'd passed it on to Harry, and he certainly knew that Harry had been making mysterious partial appearances in Hogsmeade - so when he found signs of a scuffle and a dropped Invisibility Cloak at the foot of the Willow he would suspect that Harry, at least, was down that tunnel with Black and the werewolf. And he went in alone to save him, into what he thought was the most extreme danger, into a situation which must have been one of his worst nightmares made real.
In Harry's fourth year, he sprinted through the castle in his nightshirt - ignoring a break-in to his own office on the way - because he heard somebody screaming. We know the opened Triwizard Egg sounds like somebody being tortured; we know Snape's office is well down the dungeon corridor, quite far from the steps up to the Entrance Hall, and his quarters are further down still because he passed his office en route; we know Harry and Filch were on the first or second floor and we know Snape arrived only two or three minutes after Harry dropped the egg. And he didn't seem to have spent any time assessing the situation to find out why somebody was screaming - it could have been a Death Eater raid or another monster, but he just charged in, because he thought somebody was hurt. And in this case, it wasn't his love of Lily which drove him, because he had no reason to connect the screaming with Harry, and did not do so until he was on the spot and saw the egg and the Marauder's Map. He just heard screaming, and ran towards it, straight from his bed.
In Harry's fifth year, he taught Harry Occlumency, although doing so must have put him in a knife-edge position vis-à-vis Voldemort. Already on probation, he risked angering Umbridge further by telling Crabbe to stop throttling Neville (not a light matter - if he'd lost his job, and Albus hadn't been reinstated and re-hired him, he would have lost most of his usefulness to Voldemort), so again we see that he will protect the children generally, not just Lily's son.
In Harry's sixth year, he shot through a closed bathroom door, livid in the face (that is, ashen with fright), because a girl's voice had just screamed "Murder!" - probably not knowing who had been attacked or by what or whether it might kill him too. In this case he may have seen Harry go in, and have thought it was him he was protecting. But his behaviour to the injured Draco - not just saving his life but reassuring him that he wouldn't be scarred - suggested genuine caring.
We see in DH that he stayed at the school to protect all the children, even though Harry was no longer there. We see Dumbledore ask him to do so, even though being Headmaster must have been a miserable, thankless task, with most of his colleagues ranged against him. Of course, it could be said that refusing to take on the rôle would have put him in danger by displeasing Voldemort: but we know he didn't accept the job just to save his own skin, because he took the risk of defying or circumventing the Carrows in order to make sure Neville, Ginny and Luna would receive a punishment for their raid on his office that was so mild it was really a reward. And then he put it about that he'd had them horribly tortured, so it's clear he knew it would be risky to have the Carrows find out what he'd really done with them.
JKR seems to regard Snape's sarcasm as a form of bullying, and perhaps on one level it is; but if so it's a form of bullying which is culturally sanctioned and regarded in some quarters as an art form. It's important, when trying to understand Snape, to remember that he comes from what seems to be the industrial north of England - an area where sarcasm is the norm, tactlessness, known as "being blunt", is valued as a proof of honesty and the height of praise is "not bad". Lest anyone thinks I'm making that up, consider the following Andy Capp cartoon, set in the North of England circa 1980:
The UK Reader's Digest actually runs an occasional humour section called "Great teacher put-downs of our time", including for example this, lifted from the pages of the Times Literary Supplement: "To an impudent pupil screwing up his face at a request: 'You can take that silly mask off now, Gavin. The carnival's over.'"
Snape's sneering at his students, whilst it may seem harsh by modern standards, is mild compared with what were standard teaching practices until the mid 20thC. Not very many decades ago, Neville would have been made to wear a Dunce's Cap and stand in the corner for his classmates to jeer at him; this kind of thing was still going on in some schools into the 1960s and Snape may well have encountered it, and come to regard it as normal.
A friend who was a secondary school teacher in the 1960s said that he thought Snape's level of classroom sarcasm was excessive rather than normal, but that he had seen teachers who did act like that and he considered it to be a sign of insecurity. The real-life teacher on whom Snape was partly based had to develop a strict, snappy classroom persona in part to compensate for the fact that even in his middle thirties he still looked about eighteen, and Snape, as we know, began teaching when he was only twenty-one and really was not much older than some of his students.
It may be instructive to look at some real-life sarcy schoolmasters. The first quote sets a context for Snape by showing the behaviour of a genuine boarding-school tyrant, albeit in the 1920s. In his essay Noulded into a Shake, the late great essayist and raconteur Patrick Campbell, 3rdBaron Glenavy, described what happened when a master known as Bill the Bull caught him reading a book on ventriloquism in class. Young Patrick is practising his smile, as the book recommends, when Bill notices.
Bill then seizes Patrick by the ear, drags him up in front of the class, encourages the other boys to jeer at him, and forces him to try to pronounce a difficult sentence without moving his lips or facial muscles, "encouraging" him by hitting him over the head with a ruler, hard, every time he makes a mistake. This ordeal continues for a further twenty-five minutes, with the rest of the class whooping and baying every time Patrick is struck.
Snape is nothing like so vicious as this truly bullying teacher. He does read aloud a very short but embarrassing article which he catches Harry reading in class, but the ordeal is over in a minute or two, and he is never violent (except when he hauls Harry roughly away from the Pensieve). He seems more like the teacher described by Wynnleaf on the Loose Canon discussion group on Yahoo.
The third example is from the newspaper columnist Allison Pearson, writing in The Daily Mail on 28th March 2007:
Indeed, one of the oddest things about Snape is that he is presented as so dislikeable, when in real life such teachers are usually well-liked. Half-drowned Dracula, a British fanwriter who is a current high-school student, commented that "I’ve found that certainly in English schools at least, the young, mocking and sarcastic teachers are always the most popular. Which is why it confuses me as to why Snape was not". But we don't really know much about how Snape is regarded by his students at large. Hagrid does say in PS that "Snape liked hardly any of the students", and Percy says "He teaches Potions, but he doesn't want to", so he does have the reputation of being sour and unhappy in his work, but that doesn't necessarily tell us whether or not the students like him.
We know that Harry, Ron and Bill Weasley dislike him, Neville is scared of him, and Tonks is annoyed by his comments about her new Patronus. In their first Potions lesson Ron says that he has heard that Snape "can turn very nasty"; but since Ron has had no direct experience of Snape yet, this information presumably comes from his brothers - and we already know that Bill dislikes Snape.
On the other hand, although Hermione dislikes Snape's bias against Harry she does not otherwise seem to object to him, and in fact defends him to Harry and Ron. His Slytherins seem to like him, which suggests he is a reasonably pleasant house-master, and he is not, in fact, especially punitive.
He takes points freely (although usually only five or ten at a time) and is arguably rather biased in doing so - probably as a part of his rivalry with McGonagall over the House Cup. But his reputation for fierceness in other ways seems to be just part of his performance. We see him threaten Harry with expulsion, or with the taking of enormous numbers of house points if he doesn't behave himself, but up until the Sectumsempra incident we only actually see him give Harry detention twice in six years, plus two detentions to Ron and one each to Neville, Crabbe and Goyle.
In addition, we are once told that he keeps Harry back after class to scrape tubeworms off the desks, and this delays Harry for probably about twenty minutes (Ron has finished lunch by the time Harry gets to the Great Hall, but there's still plenty of lunch-break left). But we don't know whether that is a punishment or just Harry's turn on some sort of rota, nor are we told whether or not Harry was the only person so delayed. It could have been the case that one person from each working team had to stay to clear up.
It may be that there were other detentions we're not told about, but that must apply to McGonagall too - that we don't see every disciplinary action she takes - and during the same period that we see Snape hand out seven detentions (two of them to Harry), we see her dish out twenty-two (seven of them to Harry), as well her heavy-handed punishment of Neville for something which really wasn't his fault. For carving Draco up with a magical knife, Snape gives Harry six or seven detentions (every Saturday morning from mid-May until what should have been late June), which McGonagall considers very lenient. Despite his abrasive manner, as far as we are shown he's actually much less harsh than Minerva herself is.
Note, also, that during the "I see no difference" incident, of which more anon., Harry and Ron are aggressively rude to Snape, and he punishes them by taking points. Pansy and her friends jeer at Hermione but they make sure Snape can neither hear nor see them, showing that they expect he would pull them up on it if he caught them, and we are also told that Draco waits until Snape's beck is turned before flashing the POTTER STINKS badge. Conversely, when Draco is mouthy to Hagrid about Hagrid's "voluntary" four-nights-a-week Skrewt-watch (which becomes mysteriously compulsory when Draco tries to get out of it), Hagrid doesn't actually punish him, it's true: but he threatens him with the illegal punishment of being turned into a ferret again, and allows the Gryffindor students to laugh at Draco loudly and openly.
Of course, two wrongs don't make a right. But Minerva's punitive attitude and open sneering at Neville in front of the class, and Hagrid's inappropriate threat of a humiliating and illegal punishment and his allowing a student to be subjected to open mass ridicule in class, show what kind of teaching-practice is regarded as normal and acceptable for staff at Hogwarts. It is against this background that Snape should be assessed.
Nevertheless, there is certainly room for improvement. The central joke in HBP is that Harry and Ron think that the Half-Blood Prince with his bezoar and his silver blade is a much better teacher than Snape, not knowing that he is Snape. On the one hand, this shows that they can learn from Snape when they aren't too prejudiced to pay attention to him; but it also suggests that Snape would have taught Harry and Ron better if he had tried harder to share his enthusiasm for the subject rather than nagging them. Slughorn's idea of getting people to try potions which are fun and interesting is a good one.
Snape is undoubtedly hostile and sometimes unfair to Harry: the question is why, apart from the obvious "Harry looks like his dad, who bullied Snape ragged." As SGCbearcub pointed out, mutual hostility makes it less likely Voldemort will expect Snape to influence or kidnap the boy, but he does also seem genuinely to dislike him. Bias, however, would imply that he knowingly treated Harry differently from other people for the same behaviours - and while there may be a few instances of that I would argue that the main problem is that he thinks he is treating Harry fairly, according to what he thinks he knows about him, but what he thinks he knows about him is often wrong.
When Harry arrives at Hogwarts, Snape probably knows nothing about him except that he is his parents' son, and that he precipitated Voldemort's downfall. It's strongly indicated that most of the staff go home for the summer, so there are only a few days between Snape returning to Hogwarts and his first lesson with Harry. Unless Dumbledore or Hagrid himself briefed him on what Hagrid discovered, during those few days, he doesn't know the Dursleys neglected Harry, nor that they raised him in ignorance of the magical world: and since Dumbledore hadn't briefed Hagrid on what Mrs Figg knew, he seems to be keeping information about Harry's upbringing to himself. McGonagall objected to Harry being placed with the Dursleys partly because Dudley was obviously spoilt: if she's said so to Snape, he'll be primed to see Harry's cheeky, offhand manner as due to being arrogant and spoilt like Dudley, rather than sullen and neglected. And he will want to believe that Harry is spoilt, because it's partly his fault that Harry is an orphan and living with the Dursleys, so if he admits to himself that Lily's son is being abused that's another load of guilt on his shoulders.
As well as wanting to believe that Harry is the Dursleys' pampered darling in order to ease his own guilt, he also probably resents the fact that Harry is lauded as The Boy Who Lived, when he knows that the credit properly belongs to Lily. And he knows that Harry is the thing that Lily died for, the thing that made him, Snape, responsible for her death. It's not fair to blame Harry for that, since he had no choice in the matter, but it's understandable that Harry's fame makes Snape angry.
At the Sorting Feast, Snape is probably already very uneasy about meeting the son of the woman who was his best friend and the love of his life, and of the man who was both his tormentor and his saviour - and both of them his inadvertent victims. He feels great guilt about Lily's death, and it's that guilt, at least initially, and the need to protect Harry in order to expiate his guilt, which keeps him stuck in a job he hates, and which will later compel him to resume spying. So Harry is simultaneously his victim, his motivating raison d'etre and his jailor.
Snape is talking to Quirrel when he sees Harry glaring at him in apparent hatred, and putting his hand up to his forehead in a gesture reminiscent of James, who was always fiddling with his hair. We know that proximity to Quirrelmort has made Harry's scar hurt: but just as Harry connects the pain with Snape, not Quirrel, so Snape must think that glare is for him and that Harry has been raised to hate him. And that's going to hurt particularly, because it means that he looks at Harry's eyes, which are Lily's eyes, and sees in them the same coldness and contempt that he saw in Lily when she rejected him.
[If you go to the Artnatomy site and select "APPLICATION", "NATURALISTIC MODEL" and "LEVEL II", and then click on the facial expressions for pain and anger, you will see that they are very similar. Anger has a more open eye - but it is difficult to see the eyes of someone wearing glasses and some distance away.]
Then, both of them probably feel uncomfortable being near Quirrelmort, but they associate that unease with each other. And both of them have an association with Voldemort - Snape has the Mark, and Harry the Horcrux - which they can probably sense in each other without knowing why. They give each other the creeps.
Then, Draco is a whiner, and the son of Snape's friends, and even though it's not in the books I have it on good authority that JKR told Tom Felton that Snape is Draco's godfather. We see later, after the incident with the Invisibility Cloak in Hogsmeade in PoA, that if Draco has a grievance against Harry he runs and tells Snape about it. By the time they get to the first Potions lesson, Draco has probably told Uncle Severus that the famous Boy Who Lived was nasty to him on the train - and, being Draco, he won't have told him what he did to provoke Harry. This will confirm Snape in his expectation that Harry is just James-Redux, picking on Draco on the train for no reason the way James and Sirius picked on him.
What's more, if Draco tells Snape that Harry and Ron were nasty to him on the train, and seemed to have palled up, that will make it far worse. Snape doesn't know which if any of his older brothers Ron might resemble, but his most recent experience of Weasleys has been the Twins, who are spiteful and bullying especially towards Slytherins (we see them hiss at a small child for having been sorted into Slytherin, knock Draco down and then step on him, and put Montague in danger of death from thirst or starvation). Obviously Snape will be primed to expect that Harry and Ron are another pair of arrogant bullies.
So, Snape comes to class expecting to dislike Harry, and assuming Harry pre-dislikes him. He sees Harry sitting with Ron and exchanging raised eyebrows with him during Snape's keynote speech. He then asks Harry three questions which Harry cannot answer. Was it reasonable to expect Harry to be able to answer, or did he set the boy impossibly difficult questions with the intention of showing him up?
Harry received his Hogwarts letter in late July, a week before his eleventh birthday. We know that all students get their Hogwarts letter circa late July, rather than all getting them a week before whenever their eleventh birthday is, because Tom Riddle was born at New Year and when he gets his visit from Dumbledore there is no mention of Christmas celebrations, and the next year's book-list is already out. Clearly, Tom got his letter the summer after his eleventh birthday, not a week before it.
Therefore, although Hermione is nearly a year older than Harry she too has only known about Hogwarts for about six weeks. She hasn't had much chance to load up on extra books yet, and although she probably did get a few non-course books along with her set texts, if the question which Snape asked was a really obscure one it would be a remarkable coincidence if her very first book-buying expedition had just happened to include a randomly-selected Potions book with that one in it.
Hence, the fact that Hermione can answer the questions implies the answers are in the set books, and we know Harry had read his set books with great interest. We also know that Magical Drafts and Potions by Arsenius Jigger, the Potions textbook which Harry bought five weeks ago and supposedly read with interest, is a large compendium which covers Potions all the way to OWLs, because no other Potions textbook ever appears on Harry's summer booklist until sixth year.
The asphodel and wormwood question relates to the Draught of Living Death, which isn't taught until sixth year, so it was probably only mentioned en passant in what is probably a very large first-to-fifth-year textbook and it was rather harsh of Snape to ask Harry about it. But when Harry couldn't answer, he went on to ask him two increasingly simple questions, about the bezoar and then about the names of aconite - the latter being a question which could have been answered by a Muggle and is probably in Harry's Herbology text, as well as the Potions one. Since Snape couldn't know in advance that Harry wouldn't know the answers, it looks as if he was giving Harry the chance to save face by getting at least something right, rather than intentionally showing him up. So he must have been doubly irritated when Harry couldn't answer even the simplest question, and then was cheeky about it.
It was a little nasty to quiz Harry on the set book on the very first day, but not unreasonable, especially as Harry is the son of an "exceptionally bright" father and a mother who was, along with Snape himself, one of the best Potions students Slughorn ever taught. Snape was perhaps hoping for great things from Lily's son, and was disappointed to find he'd got a dead weight instead of a star. And if he doesn't know that Harry was raised in total ignorance of his family, then he may think that Harry should have paid special attention to his Potions set-book, out of respect for his mother's memory, and his lack of interest in Potions is an insult to Lily.
There is another possible layer to that scene, although I'm not sure if JKR intended it. In the Victorian Language of Flowers asphodel - which is a type of lily - means "My regrets follow you to the grave", and wormwood means "absence". Wormwood is also a traditional/Biblical symbol of bitter sorrow, as in the phrase "gall and wormwood". It is possible that Snape is actually passing Harry a secret message meaning "I bitterly regret Lily's death", which for some reason he expects Harry to understand - perhaps there was a section on the Language of Flowers in one of the set-books, and in any case many people would at least recognize the juxtaposition of wormwood, bitterness, with a lily. If Snape doesn't know how little education Harry has, he may think that Harry has understood his expression of regret and rejected it, slapping him down.
Snape does start the class with an antagonistic attitude to Harry, since he calls him "Our new - celebrity" during roll-call, before Harry has had a chance to do anything annoying, and when Harry fails to answer the asphodel-and-wormwood question he says "fame clearly isn't everything". This isn't as nasty as it sounds, because Snape doesn't know how ironic, unexpected and to some extent unwanted Harry's celebrity is: he expects Harry to be a vain, attention-seeking showoff, like James. If he had introduced Draco to the class as a celebrity Draco would probably have stood up and taken a bow, and James was cast from the same mould: so Snape, expecting Harry to be James redux, has no reason to think his barbed comment will cause Harry more than mild irritation.
Nevertheless, it is barbed. To some extent this is because Snape can hardly open his mouth without cattiness occurring, but it does suggest that he has a problem with Harry's iconic status. It may be that Draco's version of his quarrel with Harry on the train has given Snape the impression that Harry is an arrogant lout who trades on his celebrity, or it may be that he himself resents Harry's fame: perhaps because it properly belongs to Lily, perhaps because he himself risks his life in secret for the good of the Order and gets only blame for it, while Harry gets free acclaim for something he didn't even do. He also seems to have a fixed and completely wrong idea that Harry is lazy and inattentive because he thinks he's too cool to work.
Nevertheless, Harry is lazy and inattentive, and Snape already had reason to think so by the time he started quizzing him. After Snape makes his introductory speech, Harry and Ron look at each other with raised eyebrows - a gesture which usually indicates query, sneering or dismissal. Snape is bound to notice, because he'll be wary of both - Harry in case he's like James, and Ron in case he's like the Twins. He doesn't know whether those raised eyebrows mean scorn for the subject or for him, dismissal because they know it all already, ironic interest in his dramatic speech or some private matter they shouldn't be discussing in class. Quizzing Harry is a good way to find out whether Harry is offhand because he knows the subject already, or because he has no interest in it. And what he learns is that Harry either hasn't read his textbook or, if he did, he paid it so little attention he can't even hazard a guess at the questions; and that Harry isn't embarrassed by his ignorance but self-righteous and cheeky about it.
By a few minutes into the first lesson Snape already knows that Harry is lazy, uninterested and cheeky, and he expects to dislike him and be disliked, and he also has reason to be wary of Hermione - who tried insistently to answer a question which was clearly aimed at Harry, not at the whole class. Nevertheless, once the class start brewing Snape is critical of nearly everybody, Slytherin and Gryffindor alike, except Draco. That seems to be because Draco is a genuinely skilful brewer, not just because Snape likes him.
It is, of course, deeply unfair of Snape to take a point off Harry for failing to stop Neville from making a dangerous mistake, when Harry hadn't been partnered with Neville. But Snape had just had a bad fright - it's the very first lesson with this class, and already a student has been injured quite badly, and could easily have been injured very badly - and Harry was in front of him, and he was already irritated with him. I see his behaviour at that point as like that of a parent who yells "Why didn't you stop him?" at a child whose brother has just done something stupid: it's unfair, yes, but it's also human and natural. I would say that most of the problematic things Snape does are perfectly normal things to want to do, quite natural impulses - but they are often impulses like this that he really should control in a professional setting, and he isn't good at doing so.
And from there on in, it's downhill all the way. But this is perhaps not surprizing.
Harry is arrogant (even JKR says so!), lazy, sloppy, cheeky and, in Potions, altogether uncooperative. Any teacher would find him annoying, and Snape is a rather short-tempered, excitable person to begin with, always flushing and blenching and snarling. Every time he looks at Harry he is presumably reminded of the fear and humiliation which James put him through, of the crushing remorse which he feels about Lily's death and about his quarrel with her, and of the fact that the bully who made his schooldays a living hell also got the girl. It's not surprising if he is automatically tense and hot and miserable at the mere sight of the boy, and so over-reacts to the very real annoyance which Harry represents: and Harry's total lack of interest in Potions, and in academic study generally, and his passion and talent for Quidditch, must feel to Snape as if Harry is waving a flag saying "I'm much more James's son than Lily's". [Not to mention that by beating Snape's team at Quidditch Harry gives McGonagall an excuse to gloat.]
Snape's dislike of Harry is reinforced by the fact that he guarded Harry's life, at the cost of his own social standing in the staff-room, and not long afterwards he overheard Harry and Ron saying that everyone hated him and they hoped he was ill, or had been sacked. [This scene mirrors the one in which Hermione overheard Harry and Ron disparaging her in first year, which may have been an intentional hint that the boys would eventually learn that, like Hermione, Snape had hidden charms - although sadly they learned it only after his death.]
He's bound to resent Harry's celebrity, because Harry is getting the credit for something which was actually done by Lily, and which is a constant reminder of Snape's involvement in her death; and because Snape himself risks his life with great courage and gets no credit for it. If the other staff members pity Harry for what they have learned about his home-life Snape is going to feel disgruntled about that too, because from what we see his own home-life was probably a lot worse, and nobody gave him universal acclaim and a fortune to make up for it, or took the House Cup away from another house, humiliated them in front of the whole school and then gave it to him as a present for disobeying the rules. And when everyone is telling him Harry is so wonderful, he's bound to assume the reverse out of contrariness.
Harry is the thing Lily died for, and yet he hardly seems interested in her: he only ever wants to hear about James. Even when he has Slughorn there, who doted on Lily, Harry doesn't bother to ask him about her. Snape may also partially blame Harry for Lily's death or, like Remus, be angry with Harry for taking stupid risks with the life his parents died to save. A sort of sibling rivalry is also possible: Hagrid, Snape and Harry are all on some level Albus's foster-sons, and Snape may fear that Harry will supplant him in Albus's affections.
In HBP, after Harry cut Draco, we see that Snape can do a certain amount of Legilimency without performing a formal spell. He probably senses that Harry constantly lies to him, yet doesn't know that Harry is usually protecting someone else. He will know that Harry despises him - the touch of Harry's mind must feel horrible to him, and be a constant reminder of his rejection by Lily. If he feels the trace of Voldemort in Harry, without knowing about the Horcrux, he may think Harry is both deeply creepy and another potential Dark Lord - especially after he sees that the boy is a Parselmouth.
In later years, Snape sees that Harry idolises Sirius and James and doesn't seem to care that they bullied him ragged and nearly killed him. After the Pensieve incident he believes Harry is jeering at him, that Hary has seen him stripped, that Harry is an extension of the gang of bullies who made his teens a misery. That he to some extent reacts to Harry as if Harry were James is inevitable.
And Harry, of course, reacts to Snape as he would to Vernon - which is understandable, but just perpetuates the cycle of I-hate-you-because-you-hate-me. One of the recurrent riffs in these books is people finding out information too late for it to do any good - Dumbledore learning how neglectful and emotionally-abusive the Dursleys were after the event; Harry not finding Sirius's two-way mirror until it was too late to use it and so on.
If somebody had actually said to Harry at the outset: "Snape has trouble tolerating any bad behaviour by you because your father treated him the way Dudley treats you, and so he's really jumpy and paranoid about you", Harry would have made a special effort to be pleasant and polite and that would have broken the cycle before it had properly begun: but he didn't find out why Snape was so wary and primed-to-be-hostile until the enmity between them was too well-established to be broken. Or if, instead of just dismissing Snape's concerns, Dumbledore had said: "I know Harry is chippy and defiant but he's not arrogant like James, it's because his family bullied him very badly", instead of telling Snape that he was imagining that Harry was chippy and defiant, then Snape would have made an effort to be more patient.
But instead, they were left to get on each other's nerves so badly that by the time they found out these important points about each other, their enmity was set in stone. Even so, they nearly managed to get onto a more civil footing during the Occlumency lessons, until Harry's (or Tom-in-Harry's) nosiness blew it.
By Christmas 1992, the Trio had engineered a potentially lethal accident (if a drop of Swelling Solution had splashed into someone's mouth they could have choked on their own tongue) which injured several Slytherins, in order to create a diversion while they robbed Snape. He must be pretty sure it was them, because the ingredients for Polyjuice were taken, and then Hermione turned up furry.
And because the ingredients were stolen from his private store he may have had to pay for them. The ingredients they stole were hard to obtain and therefore probably very expensive, and we know the Potions master's salary isn't good (Slughorn complained about it after he'd insisted on a pay-rise, although admittedly Snape probably gets a bit extra for being Head of House) - so if he did have to pay for them it would have been a distinct hardship.
By the end of third year he knows that the Trio threw him into a wall, to his life-threatening injury (any period of unconsciousness resulting from a blow and lasting more than ten minutes is potentially fatal), and then did nothing to help him. Eventually he'll understand they had to stop him arresting Sirius, but since a bad blow to the head usually wipes the memory of what happened immediately beforehand, he probably doesn't know that they were only trying to disarm him, and that bashing his head was an accident.
He was unconscious for almost an hour, so he probably does realize, from the length of time missing out of his evening and the fact that he didn't wake up in the hospital wing, that they left him bleeding on the ground and didn't seek medical assistance for him, because what they were talking about was more interesting to them than whether he lived or died - whether or not he knows that they let Sirius brutalize him while unconscious. Disarming him was necessary and knocking him out was an accident, but their failure to render assistance to an injured man showed a criminal degree of callousness, and in real life they'd probably be charged with assault.
He knows that when he heard Sirius boasting about how he had nearly murdered him and saying that he'd deserved it, and he dared to resent it, Remus sneered at him and dismissed his anger as "a schoolboy grudge", and Harry called him "pathetic". He has every reason to think that they regard his life as of no account - and he'd be right. They do. We're specificially told that Harry thinks unconscious!Snape looks "lifeless", yet he shows no concern and does not alert Remus to Snape's condition.
Pause for a moment and consider what McGonagall would do to three Slytherins who deliberately injured several classmates, robbed her of dangerous substances, threw her into a wall and then left her unconscious and bleeding for the best part of an hour. Yet, the sum total of Snape's revenge is that he becomes a little more obstructive towards Harry, and possibly makes one catty remark about Hermione's teeth, although his meaning in that scene is ambiguous. This is a bit childish, but hardly the action of a vengeful brute - if anything, it suggests that he's as soft as butter.
Since Snape is a family friend of the Malfoys, he presumably knows that at the end of both fourth and fifth year Harry and his friends left Draco and his friends to suffer for many hours on the train with severe magical injuries, without treatment or even a drink of water. Draco will of course not have told him about his own part in this, but even given that Draco provoked the situation, Harry's behaviour was very callous.
Of course, many readers see Harry's violence, thefts etc. as just cartoon violence, not serious. But if Harry's history of sabotage, theft, leaving people he doesn't like to lie severely injured and unconscious without any medical treatment, practising hexes on a Squib who can't fight back etc. is just cartoon violence, then Snape's overbearing and sarcastic classroom manner must be just pantomime aggression. If Snape is to be judged as if he were a real teacher, Harry must be judged as if he were a real student.
When Harry performs well, Snape stops criticizing him - which suggests that it is largely Harry's laziness and lack of interest in the subject which angers him (and also perhaps that Snape gets angry with Harry in Potions because he expects Lily's son to be able to perform better than Harry in fact can). When Harry gets between Snape and Sirius in the kitchen at Grimmauld Place - being more sensible and mature than the two adults at that point - only Sirius objects. Snape accepts Harry's intervention without complaint, presumably because Harry is being both impartial and competent.
During Occlumency lessons Snape twice praises Harry when he does well: a bit grudgingly, OK, but he seems to come from the industrial north of England where "not bad" is a high compliment, so the fact that he praises Harry at all is remarkable. In fact, Harry and Lily are the only two people we ever see him praise directly, although he once praises Draco indirectly by showing his potion-preparation to the class as a good example. Generally, his esteem is shown by not criticising (and since he doesn't criticise Hermione's potions, he must esteem them highly).
'Well, for a first attempt that was not as poor as it might have been,' said Snape, raising his wand once more. 'You managed to stop me eventually, though you wasted time and energy shouting.' [OotP ch. #24 p. 472]
'Reparo,' hissed Snape, and the jar sealed itself at once. 'Well, Potter ... that was certainly an improvement ... [cut] I don't remember telling you to use a Shield Charm ... but there is no doubt that it was effective ...' [OotP ch. #26 p. 522]
'You've got loads of magic,' said Snape. 'I saw that. All the time I was watching you ...' [cut] [cut]'You're not going to end up in Azkaban, you're too --' [DH ch. #33 p. 535/536]
Even when Harry breaks through into Snape's memories, and is sure he'll be punished, Snape praises him. It's only when he sees the memory of Cedric's murder, and when he realizes that Harry isn't trying to keep Tom out of his dreams, that he becomes angry.
Snape is quite chatty during the Occlumency lessons, and gradually stops insisting on Harry calling him "sir". He's more open with Harry than any other Order member except Sirius, provided you don't mind Service with a Snarl. This openness and willingness to praise may be because he has taken out the worst of his emotions about James and about his quarrel with Lily, and so Harry's appearance no longer freaks him out so badly.
[There is an anomaly, incidentally, between the hardback and paperback versions of the scene where Harry repels Snape with a Stinging Hex. In the hardbacks, both US and UK, Snape reacts with close interest - in the paperbacks, with contempt. This seems to have been part of a general editorial decision to reduce the number of times the expression "watching [him/her/it]closely" appears in the book, rather than a conscious desire to make Snape seem nastier.]
Snape talks up getting Harry expelled, but whenever he has something serious on him he doesn't act on it. When Harry is caught with the frozen Mrs Norris, Snape is fair about his possible innocence. He must know, when Hermione turns up furry, that it was the Trio who robbed him but he does nothing about it. When they throw him into a wall he assumes they were Confunded (he does make noises about getting Harry suspended, but as this is only a few weeks from the end of the school year it's hardly a dire threat). When he thinks that Harry has robbed him again, he simply issues a warning. Even when Harry almost kills Draco he only gives him detention - which McGonagall says is lenient.
The only time he really tried to get Harry expelled was over the flying Ford Anglia. Ten minutes beforehand he had listened to Harry and Ron saying how much they hated him and how they hoped he'd been sacked, despite Harry knowing that Snape probably saved his life in first year - so Snape must have felt that if they wanted him thrown out, it was reasonable for him to want them thrown out.
The rest of the time, whenever he really could get Harry into trouble he back-pedals. Talking about expelling Harry is apparently just his way of blowing off steam.
In truth, he desperately needs either Harry or Neville to succeed: his own hope of long-term survival depends on one of the boys who fit the prophecy killing Tom. And he would probably much prefer it to be Harry. If Harry fails, or proves not to be the prophecy child after all, then Lily's death was pointless, and Snape's inadvertent betrayal of her was just a betrayal, and not the means of Tom's downfall. Harry's laziness, sloppiness and needless risk-taking will infuriate him all the more because they increase Harry's risk of failing, taking with him Snape's hope for life and whatever good there was in Lily's death.
Snape certainly appears at first glance to be biased over house-points. He takes points off Gryffindor for very minor infractions, while Slytherins seem to get away with misbehaviour. We are told in CoS that Draco flicks puffer-fish eyes at Harry and Ron and they don't retaliate because if they did they know they would get detention, which they consider to be unfair. This seems to be included in a description of "the usual way" Potions class goes, so at first sight it seems to be evidence of Snape's bias.
However, although we are told that Harry and Ron "knew" they would get detention if they retaliated, we in fact only see them get two detentions each from Snape over the course of six years, prior to the Sectumsempra incident. Although there may have been other detentions we aren't told about, this does suggest that Snape has managed to give them the impression that he is very ready to hand out detentions, without actually doing so. This in turn suggests that they are only guessing about what would happen if they retaliated, which in turn suggests they haven't actuallty tried it.
We see McGonagall too come in at the end of a quarrel between Harry and Draco and punish Harry (after the Quidditch match in OotP), and in fact this is such a well-known phenomenon that it was commented on in the February 2009 Reader's Digest, viz.: "Great Truths Learned by Small Children: If your sister hits you, don't hit her back -- they always catch the second person."
In fact, we are shown that the Slytherins reserve their most serious sins for when Snape's back is turned, showing that they know they wouldn't get away with it if he caught them at it. This suggests that his bias consists in trusting his Slytherins to behave better than they in fact do, and believing them when they claim to be the innocent parties in any incident, rather than knowing that they are misbehaving and consciously allowing them to; just as he could never see any fault in Lily, even when she treated him badly. So his fault is a pair with Hagrid's trust of Aragog - it springs from too much blind love and trust rather than malice.
Nor are the Slytherins any worse than the Gryffindors: Snape's failure is a failure to see that his own students are sometimes as bad as the Gryffindors, or that Draco is a trouble-maker. In the first few years, relations between the houses were much less polarised. Students of all houses cheered Hagrid's appointment, although Gryffindor cheered the loudest, and all the Slytherins in Harry's class cheered Harry's riding of Buckbeak, except for Draco and his immediate cronies. It was only after Draco's injury that the other Slytherins turned against Harry.
We see that Draco and his friends jeer at Harry at every opportunity, and that Pansy and her friends jeer at Hermione. The Slytherins publicly insult Harry over the Triwizard Tournament, and Ron over Quidditch. But the Gryffindors can be just as verbally cruel, and a lot more violent.
In GoF, when Draco is reluctant to spend alternate evenings watching and making notes on Blast-Ended Skrewts Hagrid threatens to turn him into a ferret again (deliberately mocking him with the reminder of a humiliating, physically agonising and illegal punishment inflicted by somebody who was in fact a Death Eater, and who was believed at the time to be a member of a KGB-style security force which routinely tortured and killed its prisoners), and we are told that "The Gryffindors roared with laughter". Lee Jordan's Quidditch commentary is outrageously biased. Fred and George hiss at an eleven-year-old just because he has been Sorted into Slytherin; and later shut Montague in a broken magical device which could easily have killed him - especially as they casually expect that he might be trapped in it for weeks - and which did injure him so severely that he was still needing to be spoon-fed medicine two months later. Harry and co. leave Montague to suffer in the hospital wing, rather than give Madame Pomfrey information which might help him.
Even Draco's vicious attack on Harry at the start of HBP is tit-for-tat for the incident at the end of the previous term, where the DA crowd hit Draco, Crabbe and Goyle with so many curses that they resembled giant, oozing slugs. Draco had started it by ambushing Harry: but the three boys were left with magical injuries which could easily have proved life-threatening, and which must certainly have been extremely painful, and instead of trying to get medical help for them Harry and his friends stuffed them into the luggage rack and left them for eight hours without food or water or even a lavatory break. They thought it was hilarious that a week after losing her husband to Azkaban, Narcissa Malfoy would have to deal with serious injury to her son and his friends.
At the end of the previous year, too, Harry and his friends had hexed Draco, Crabbe and Goyle on the train and left them to lie for several hours unconscious and untreated with significant magical injuries, and the Twins deliberately trod on them. On that occasion, Draco had merely been mouthy. It seems to be a common pattern that Draco and co. are verbally provoking and Harry and co. respond with physical or magical violence: and since verbal provocation apparently isn't against Hogwarts rules, and violent retaliation is, Snape is bound to feel that Harry is behaving worse than Draco.
Slytherin is also isolated and ostracised by the other houses: we see that whoever Slytherin are playing at Quidditch, all three of the other houses automatically support whoever is opposing Slytherin. So Snape will have a feeling that his students are being excluded and bullied - and that he himself is still being excluded and bullied through them - even though they have to some extent brought this situation on themselves through their dubious Quidditch tactics.
So, it's not the case that Snape presides over a house of students who are clearly more vicious than all those around them, and turns a blind eye to their crimes. In a school with a generally vicious culture, he tends to assume that his Slytherins are - as he was - more sinned against than sinning, and fails to see (because they take pains that he should not see) that they are often as bad as their opponents.
Gryffindor and Slytherin are the only two houses we really see Snape interact with much. We only ever see him take points from the Trio or (once) Neville, and from the couples in the bushes: but we only ever see McGonagall take points from Draco or from Gryffindors, usually from the Trio or Neville (70 points from Draco, 110 from the Trio, 50 from Neville and 5 from Angelina). This tends to suggest either that Harry only notices points taken from his immediate circle, or that Snape takes points from the Trio and Neville because they are, indeed, especially annoying and ill-behaved: since even their own house-mistress punishes them much more often than other students.
At the start of first year Ron says that 'Snape's Head of Slytherin House. They say he always favours them', so we know he does have the reputation of favouring his own house-students over everyone else, and in PoA Harry thinks that Snape "generally favoured his own students before all others": apparently even Harry doesn't think that he is biased against Gryffindors, as such, but just over-indulgent towards his own house. But to some extent this is true of McGonagall as well, who favours her own house at least as regards Quidditch, and is prepared to bend the rules to get an advantage by e.g. allowing a first-year to have his own broom. Only once do we see her give points to a non-Gryffindor (Luna), although it's true we don't see her interact with other houses much.
Dumbledore too is biased in favour of his own former house, to some extent. His decision to hand Harry the House Cup over the heads of Slytherin in first year may be bias in favour of Harry personally, and it may be that when he acts as if Harry's preference for being in Gryffindor is a proof of virtue, he is simply impressed by the fact that Harry chose against the tendencies and pull of the Horcrux: but when he takes Snape's great courage as proof that "we sort too soon" he is clearly suggesting that usually it's only Gryffindors who are courageous, and insulting Snape's own house in the process. So bias in favour of one's own house is a Hogwarts norm, even among the staff.
Snape does give detentions and lines to Slytherins. He disciplines his house students in private, away from the eyes of other houses - as McGonagall also tends to do - so he is probably stricter with them than Harry gets to see. This suggests that any possible unfairness over house-points is due to wanting to beat Minerva to the House Cup, rather than to bias. When it comes to Quidditch we are told that Snape and McGonagall are each as biased as the other.
- the implication being that if he was no less partisan he was probably also no more so.
After the Quidditch match in OotP, where Harry and the Twins thumped Draco, McGonagall and Snape each punish wrongdoers in their own house: Snape gives lines to a Slytherin team member for cheating, and McGonagall gives detention to Gryffindor team members for fighting. This incident is significant.
Most of the things Snape lets his Slytherins get away with consist in being mildly rude to other students - when they are very rude or aggressive they hide it from him. We are specifically told that when Pansy jeers at Hermione's teeth she does so silently and behind Snape's back, and that Draco turns his back to Snape before flashing the POTTER STINKS badge (Snape might still see the flash of light - but he thinks the badges say SUPPORT CEDRIC DIGGORY). Later on Draco "takes the opportunity" to flash the badge again while Snape's attention is on the Trio - presumably, the opportunity he is taking is that of Snape not seeing what he is up to - and in PoA he likewise waits until Snape's attention is on Harry before doing his Dementor impression. When Draco is injured by Buckbeak, he openly says he needs help with preparing his Potions ingredients, then drops his voice right down to ask Harry about Hagrid, and all the way down to a whisper to admit that he is exaggerating his injuries to get Hagrid sacked. The implication is that he doesn't want Snape to hear him.
When Snape catches Ron physically attacking Draco in PS, and Hagrid explains that Draco had insulted Ron's family, Snape replies "Be that as it may, fighting is against Hogwarts rules." Harry assumes Snape is being unfair: but after the fight at the Quidditch match Minerva disciplines Harry and George for fighting Draco, and she too does not regards Draco's extremely provoking rudeness to them as either a disciplinary issue or an excuse. Hogwarts students are all effectively going armed, which explains the stringent rules against physical or magical violence: whether it's fair or not it seems clear that it is indeed the case that at Hogwarts verbal provocation is not against the rules, and physical or magical retaliation is. So Snape is acting quite correctly by never punishing Draco for sniping at Harry, and it's to his credit that Draco feels he has to conceal his more extreme rudeness at all.
If Snape does have any real bias about taking house-points, then, it's probably part of the ritual of his friendship (or whatever it is) with McGonagall. But we also see prejudice against Slytherins by other houses, and Snape may feel that he has to balance that bias and show his house-students that he is as much for them as the rest of the world is against them. He also needs to balance the fact that Dumbledore and McGonagall give points so freely to Gryffindor. And taking points is all he does to balance it - we never see him give points to Slytherin, not even to Draco.
Harry, incidentally, appears on the face of it to be a better teacher than Snape: he gets very rapid results with his Defence Association/Dumbledore's Army class. But he has the advantage of Snape in that he is teaching a class all of whom really wish to learn. Even so, when he is faced with a student (Zacharias) who is cheeky and difficult he does not react well, and resorts to telling him to either shut up or leave, basically: and he demonstrates a striking teaching bias by not even considering the possibility that some Slytherins might want to pass their DADA OWLs too.
If the matter had been discussed they might have legitimately concluded that because so many Slytherins were allied with Umbridge, they wouldn't be able to tell which Slytherins they could trust - but as far as we are shown, the idea of giving equal educational rights to Slytherins is never even considered. Harry has a very definite house bias (in which he is encouraged by the Twins and Ron), and one which is based on hatred of a particular designated "other", not love of his own house: he accepts all houses except Slytherin. Snape's bias at least seems to be based on "I love my people", not "I hate your people".
Snape's house bias may be for Slytherin, rather than against Gryffindor, but he also has some personal bias against Harry and for Draco. He cuts Draco a lot of slack - but he has probably known him since he was in nappies, and he probably doesn't know what a bully he is. When Draco flashes the POTTER STINKS badge, he makes sure Snape's back is turned - showing that he expects Snape would not turn a blind eye if he caught him.
In the Buckbeak incident, Draco probably was genuinely badly injured, at least initially. Harry saw a large, deep gash bleeding copiously, and Madame Pomfrey kept him out of (or at any rate allowed him to stay out of) classes for at least a day, possibly as much as six days, and then sent him out still in bandages.
We know that Montague was trapped in the Vanishing Cabinet some time in April 1996, and at or before the end of June he was recovered enough both mentally and physically to be sitting in the common-room regaling his house-mates with his experiences. Yet, three weeks into June he was seen sitting in the hospital wing with his mouth open like a baby bird, waiting for the nurse to spoon medicine in. This suggests that he had neurological damage - he was too physically trembly and weak to hold the spoon himself - which in turn suggests that nerve damage takes months to heal, even with wizarding medicine. Neville's parents also behave as if they have actual brain-damage, not just psychological trauma, and St Mungo's has not been able to fix it. Evidently all the staff accepted the fact that Draco needed to be bandaged for two months, so it's entirely likely that he had nerve-damage which was taking a long time to heal, and he really did have persistent pain and weakness in his arm.
At the same time Draco was certainly milking his injury for all it was worth and using it to be a pest to the Trio, and Snape let him do so. There's a recurring theme in the books about people who dote too much on a child or a pet and so don't recognize its misbehaviour - the Dursleys with Dudley, Hagrid with Aragog and Norbert, Snape with Draco. But if it's a failing and a blindness on Snape's part, at least it's a failing which springs from too much blind affection.
Insofar as Snape does resent Harry for being his father's son, and if he does harbour unreasoning prejudice against another house (if he does at all), there too he resembles Hagrid. Hagrid tells Harry "There's not a single witch or wizard who went bad who wasn't in Slytherin" when he knows that one of the Gryffindor Marauders became a mass-murdering Death Eater (even if he's wrong about which). He tells Harry that all Malfoys are rotten because they have "bad blood", and insults a terrified eleven-year-old child and curses him with a painful and humiliating pig's tail just because he finds the boy's father annoying.
We know that Dudley was a bully, even at that age - but Hagrid didn't know that. All Hagrid knew was that Vernon was a loud-mouth, so he visited the sins of the father on the son, with far more cruelty and even violence than Snape ever shows to Harry, and with far less grievance against Vernon than Snape has against James. And what he was trying to do was even worse than what he did - he was trying to transform Dudley into a pig, and we're told in Beedle that human-to-beast Transfiguration destroys the subject's human mind for the duration of the change.
Hagrid was trying to to wipe out Dudley's mind and memory, at least temporarily - and we know that when Hagrid instead gave Dudley a pig's tail he didn't bother to tell Dumbledore or anybody else to come and sort it out, but instead left the child to have what must have been painful (and expensive, if it was private) Muggle surgery. If he had succeeded in turning the boy into a pig he probably wouldn't have told anybody about that either, and pig!Dudley might have run off and been killed and eaten, just to punish him for being fat and having a loud-mouthed father.
So if Hagrid gets a free pass for his truly appalling behaviour, why shouldn't Snape be forgiven his much less severe treatment of Harry?
Snape undoubtedly bears Sirius a grudge - with good reason. As a boy, Sirius set him up to be killed or infected by a werewolf (or at best, Sirius didn't care if he was killed or infected) - apparently, just because he found Snape's nosiness irritating, and he didn't want him to find out about the Marauders being illegal Animagi. If a real schoolboy tried to feed a classmate to a grizzly, or to infect them with Aids, in order to cover up a crime which they themselves had committed, would we think it was "just a prank"? And Sirius didn't even learn from Snape's near-death at his hands, but went right on persecuting him.
Nor is it just a "schoolboy grudge". Almost the first thing we see adult!Sirius do, after his thirteen-year absence from the wizarding world, is to boast about the murder attempt and say that Snape deserved it. And he's not just winding Snape up, because he doesn't know invisible!Snape is listening: he means it. And even if he just means Snape had deserved a fright, adult!Snape will certainly assume that Sirius meant he had deserved to die. His grudge, then, is not just that Sirius was vile to and about him and careless of his life when they were boys, but that Sirius is vile to and about him and careless of his life now.
Even when Sirius's life depends on Snape calming down and understanding about Peter, he can't resist sneering and saying "The joke's on you again, Severus" - reminding him of years of humiliation, and of the one particular "joke" which nearly killed him. A moment's thought should tell Sirius that although Snape is dangerously overwrought and has misunderstood the situation badly, he has committed no crime and is doing his best to protect children from what he believes is a serious threat. Yet later Sirius bashes an unconscious, defenceless and head-injured Snape's head against the ceiling - although Snape himself may not know that.
[In truth, we only have Harry's opinion that Sirius bashed Snape's head deliberately. Sirius hadn't used a wand for nearly thirteen years and now he was using someone else's wand to manoeuvre a tall, limp body down a narrow, low-ceilinged tunnel in near darkness; and the second time that Harry notices Snape's head being banged, Sirius was distracted by an intensely emotional conversation. He may just have had difficulty steering Snape. But he didn't care enough to ask for help, even though his callousness risked triggering Second Impact Syndrome - an admittedly rare condition, but one which can kill in fifteen seconds, far too fast to summon Madam Pomfrey in time to save Snape.]
Later Sirius is sneeringly unpleasant and accuses Snape of being out to hurt Harry when Snape is really trying to help him. He calls him Lucius's "lapdog", which may be exceedingly cruel of him. Given how badly Snape reacts to this comment, and the reputation of boys at British boarding schools, there's a suggestion that Sirius thinks there was a sexual relationship between Luius and Severus at Hogwarts: since Lucius is five or six years older than Severus this would have to have been at least borderline abusive, so if Sirius means what it sounds as if he means, he is jeering at Snape for having been abused. And although Sirius says he isn't proud of the way the Marauders treated Snape, he still dismisses young!Snape as "just this little oddball", as if that justified it. Before Harry knew about the bullying, Sirius relished calling Snape a "slimy, oily, greasy-haired kid" - making it clear he has no real remorse over the way he treated him.
Snape thinks that Sirius's attitude towards him is unchanged - and he's right. Nor is Sirius's behaviour a reaction to Snape's hostility in the Shrieking Shack, because Sirius's statement that young!Snape had deserved the murder attempt was made before they re-met. Snape, therefore, is carrying an eighteen-year-old grudge against his tormentor and would-be-murderer, freshly inflamed by the discovery that Sirius is completely unrepentent and still means him physical and emotional harm. Sirius is carrying an eighteen-year-old, literally murderous grudge against Snape for having been rather irritating.
Which of them is the more petty?
As far as people being immature and carrying petty grudges goes, Pottermore tells us that Minerva McGonagall is still carrying a grudge against all of Slytherin because a Slytherin player fouled her during a Quidditch match when she was about fifteen - an age which is a quarter of a century longer ago for her than it is for Snape. Dumbledore and his brother, both well over a hundred, are still acting out their boyhood rivalry and resentment. So if Snape is being childish or petty in still carrying a grudge against Sirius, there's a lot of it about.
Snape's behaviour in the Shrieking Shack seems harsh, and he certainly got hold of the wrong end of the stick and then hung on to it grimly: but Harry had been equally sure that Sirius was guilty, and equally vengeful, until about ten minutes beforehand. The Trio have reason to trust Remus and Sirius, at least enough to hear them out, because Remus disarmed them and then returned their wands to them: but Snape doesn't know that. As far as he knows Remus and Sirius haven't killed the Trio yet because they are out-gunned three wands to one.
So far as we know Snape sincerely believes Sirius is a mass-murdering Death Eater who betrayed the Potters to their deaths, making a mockery of Snape's self-sacrificing attempt to save them. He believes that this man is directly responsible for killing Lily, and since he knows Sirius is no coward he must have acted from hatred and treacherousness, not fear. He believes that Sirius betrayed his own best friend James, his best friend's wife and their baby to death, then personally killed another friend and twelve bystanders, and then laughed about it. He also thinks Sirius has preserved that hatred and callousness through twelve years in Azkaban, and has escaped and travelled across Britain with the express purpose of finishing what he started and killing Lily's son, and doesn't care if he kills other children who get in the way. The fact that Sirius really has broken Ron's leg, and had previously been seen poised over Ron's bed with a knife, reinforces this impression.
[Later Snape will be far more lenient towards Peter, who really did doom Lily. But he may believe - probably wrongly - that Peter acted from fear and weakness rather than malice or conviction, and he knows that Peter shared a dorm with Harry for three years and did him no harm.]
It seems callous that Snape is so harsh to a man who is clearly ill and emaciated: but Sirius has been free for a year, and as far as Snape knows his decision to hang around the school, starving, instead of taking himself off to somewhere where he could regain his health, is just the product of his fanatical desire to stalk and kill Harry.
He believes Remus is in league with the murderer and is sacrificing children who are under his care, for the sake of a friend - and Snape takes protecting the students in general, and Harry in particular, very seriously. [In fact Remus did worse: he endangered the children under his care just to save face.] He believes that Remus is siding with Sirius and therefore (as he thinks) condoning the betrayal and death of Lily, James and Peter, who had also been Remus's friends. Bear in mind that Sirius himself had believed that Remus was the traitor in the Order, until he saw Peter kill innocent Muggles and fake his own death, and that both Snape and Sirius know that Voldemort actively recruits werewolves, so although Snape's suspicions of Remus are (sort-of) wrong, they are not unreasonable.
The reason Snape came down that tunnel, instead of waiting at the entrance or sending a Dementor in, was probably because he thought children (or Harry specifically) were in danger. He must have been absolutely terrified, going down into the dark to confront the two people who had nearly murdered him, in the place where he had nearly died, knowing that Remus could transform at any time [it's clear that there's moonlight shining into the Shack, probably through a skylight.] And it must have seemed poetically apt, to save James's son in the same place where James had saved him, and from the very same danger - because even though James only saved him to torment him again, he does owe James a debt, because he caused James's death.
Then he heard Sirius boasting of how he nearly killed him, and saying that he had deserved it. He heard Remus claiming that the enmity between James and himself had been because young!Snape was jealous of James, rather than because James bullied him ragged. [He was jealous of James later, once James got Lily, but according to JKR initially it was James who was jealous of him because of his friendship with her. Remus probably couldn't tell the truth with Sirius in such an excitable frame of mind - but I doubt if Snape was up to being that objective.]
Overwrought though he was, Snape initially only proposed to arrest them ("Two more for Azkaban tonight" - evidently he believes that Sirius won't be Kissed on sight if he is firmly in custody). Then Remus called him a fool for minding hearing Sirius gloating over the attempted murder, and dismissed his pain and rage as a mere "schoolboy grudge" - as if Sirius hadn't just renewed their enmity and given him a whole fresh adult grudge to bear. And then Sirius sneered at him and said "The joke's on you again, Severus", referring back to the "joke" in which he had tried to murder him, in the place where the murder had almost succeeded - and it was only then that Snape started ranting about having them both Kissed. And why should he have any regard for their lives, when they'd just made it so plain that they had none for his?
It was cruel to bait Sirius with the threat of the Dementors - but he'd just been forcibly reminded of all Sirius's cruelty to him, and seen how little he regretted it. And he was lashing out from a position of fear, not strength. He must have been petrified, stuck in that place with his would-be killers; and if he thought his position was precarious he was right, as he was knocked out about a minute later.
Snape wanted to have Sirius Kissed for being a mass-murdering traitor, and Remus for abetting (as he thought) the attempted murder of a child, when they were both sneering at him and he was hysterical with rage and fear. Sirius and Remus planned to kill Peter for the same crimes, in cold blood, in front of three children, as the man grovelled for mercy at their feet. Who is the more ruthless here?
It isn't very nice of Snape just to accept the idea of feeding criminals to the Dementors, and his attitude contrasts poorly with Remus's concerns about the ethics of Azkaban. But we see in the books that Snape has to betray people or watch people die in order to keep his cover, on Dumbledore's orders, and presumably he had to do so in VWI as well. He has also had to square the necessity of combatting Voldemort, and of handing Death Eaters who trusted him over to the Aurors and, ultimately, to the Dementors, with the knowledge that his victims - many of them former friends - were likely to be tortured, killed out of hand or sent to a death camp without trial. If he hadn't convinced himself that sending people who trusted him to the Dementors was somehow acceptable, he'd have gone mad.
Altogether, he's been conditioned to accept that an authority figure has the right to do morally dubious things "for the greater good", and that he should go along with that: if he didn't, he wouldn't be able to function as a spy. And he must have tended to think that way already, to be able to join the Death Eaters in the first place - he must have thought, as Albus thought of his and Gellert's plans, "Yes, some people will get hurt, but it's for the ultimate good of the wizarding world."
Remus on the other hand is a shifty character, but his very shiftiness and immunity to rules makes it easier for him to see that what the Ministry is doing at Azkaban isn't a regrettable necessity but outright wrong. He may be mildly criminal and as unreliable as quicksand, but he's also never going to even think of "just following orders" as an excuse for anything. Depending on the circumstances his shiftiness, like Snape's rigidity, can be either a vice or a virtue.
When Snape says Harry "would have been well served if he'd killed you!" he sounds terrible - but he believes that James's refusal to think he could be wrong about Sirius led to his death, and now Harry is blindly making the same mistake. And since Harry rates Snape's life so low that he has just called him "pathetic" for minding hearing his own would-be murderer boasting about the murder attempt, why should Snape rate Harry's life any higher?
[Harry really does think Snape's life is of no account. After Snape is knocked out Harry thinks that he looks "lifeless", but seems completely unconcerned.]
In fact, far from disregarding Harry's life, Snape protects Harry especially. His anger here will be in part due to his fear for him, like a parent shaking a child who has run out into traffic.
When Snape binds Remus with cords and says that he will "drag the werewolf", he sounds callous. But he knows Remus is an imminent danger to everyone around him - including three children, one of whom is lame. The fact that James had had to rescue him from were-Remus suggests that werewolves are immune to magic and that binding one is a sensible precaution and, as we see when were-Remus jerks his paw out of the manacle, if you're going to restrain a werewolf you need to do it tightly. And the prospect of being stuck in the Shrieking Shack with an unbound, transformed Remus must be, quite literally, one of Snape's worst nightmares.
By "dragging" Remus Snape presumably means drawing him through the tunnel under Mobilicorpus. Binding Remus would be a sensible precaution even if he didn't think Remus was in league with a mass-murdering Death Eater - and if Remus had been being responsible he would have suggested it himself. Instead, the result of Remus's carelessness was that he transformed in the presence of three children and nearly bit them.
Calling Remus "the werewolf" sounds cold, but it probably means that the thought of what Remus may soon become is preying on Snape's mind - stuck as he is in the place where Remus once nearly ate him, and being still very scared of him. He may also wish to remind the children, and himself, how dangerous Remus is and why he is being so harsh.
The fact that he gags Remus and, later, Sirius again seems harsh and oppressive: but later, when Moody believes Snape to be a true Death Eater, we will see that he sets a trap meant to tie Snape's tongue. The implication is that silencing a wizard's voice is a valid combat technique, so there may be some spells which cannot be cast non-verbally, and Snape is just taking a reasonable precaution by gagging people he thinks are dangerous enemies. Indeed, the fact that the Levicorpus spell was specifically labelled "non-vbl" confirms that not all spells can be cast without a voice.
When Snape refuses to listen to Hermione, he again sounds harsh and overbearing. But he probably sincerely believes that she's been Confunded, and that anything she tells him will be mere babble. He knows how glibly convincing Sirius can be, and how little his word can be trusted - because Sirius once nearly lured him to his death.
Of course, he really wants Sirius to be guilty. He wants to blame Sirius for the Potters' deaths, not himself. For almost thirteen years he has been able to say "I told you he was a murderer, and you didn't listen and now he's killed thirteen people." For thirteen years, he has been able to pride himself that the handsome, debonair Marauder turned out to be a murderous Death Eater and the scrawny Slytherin geek grew up to be an unsung hero. He doesn't want to lose all that lovely sense of validation.
What's more, although Dumbledore lied by omission when he implied that Snape's main reason for protecting Harry was because he felt himself to be in James's debt, he had sworn that everything he did say would be true, and if it was then Snape does indeed feel himself in debt to James - even if that wasn't nearly as big a motivator as his love of Lily. Even though James probably did save him for entirely selfish motives, he would still feel "He saved me, for whatever reason, and I repaid him by betraying him to his death". Finding out that James had actually encouraged were-Remus to roam around loose, and that James probably hadn't even taken any risk to save him because he had had the option of protecting himself by turning into Prongs, would overturn something that had been an important part of Snape's view of his own life since he was sixteen, and add to his confusion and distress, by forcing him to rethink what he thought he knew about an important incident in his own life.
Later that night, Snape is still trying to have Sirius Kissed, and behaving rather hysterically. However, he was out cold for almost an hour, which indicates a really bad blow - and irrational, literally foaming-at-the-mouth rage is a common symptom of concussion.
Snape thought that Sirius was a high-ranking Death Eater (we're told that none of the Death Eaters knew the identities of all the others). He believed he had prevented this high-ranking Death Eater from killing Harry - that he had stopped one of Voldemort's minions from doing something which clearly served Voldemort's interests. In case he might have to spy again, on Death Eaters or on a reborn Voldemort, it was in his interests to shut Sirius up.
Admittedly the Order of Merlin would have made his rôle in Sirius's capture public but with Sirius gone, he might be able to come up with a version of events which would make it less obvious that he had knowingly opposed Voldemort's interests. It would be only Remus's word against his, which would probably count for as little as Dumbledore says it would count in Sirius's favour.
As much as Snape hates Sirius and thinks Sirius is a threat to his cover, when he brought him in unconscious he conjured a stretcher for him; contrasting favourably with the brutal way Sirius treated him when he was unconscious. Yet Sirius has far less grievance against Snape than Snape has against somebody who not only bullied him unmercifully and tried to kill him, but whom he believes to be a mass-murderer.
And when Albus jokingly suggests that Sirius had been sprung by somebody who could be in two places at once, thus warning Snape that illegal use of Hermione's Time-Turner was involved, and twinkles at him to let him know that whatever happened had happened with his approval, Snape swallows his rage, shuts up and goes away. And it's not obedience to Albus which shuts him up, because ten minutes beforehand he had been encouraging Fudge to have Sirius Kissed even if Albus objected.
It could be the fact that he could get Dumbledore into serious trouble for illegal use of a Time-Turner that silences him - or the realization that if Albus authorized Sirius's escape Albus must believe Sirius's claim of innocence, there may therefore be something in it, and as much as he hates Sirius he still doesn't want him Kissed if he is innocent. Either way, he forgoes revenge out of consideration for someone else.
Snape's refusal to observe Remus's Boggart-facing session may have been because he was afraid the Boggart would show Lily dying, or it may have been protective of Remus. We know that Snape is still very afraid of Remus, because when he brought Remus his Wolfsbane he backed out of the room - he wouldn't turn his back on him. There's a good chance that were-Remus is himself Snape's Boggart, so his presence might have caused the Boggart to turn into were-Remus in front of the children, risking giving Remus's secret away - as he had promised Dumbledore he wouldn't, all those years ago.
True, Snape did subsequently encourage the children to read up on werewolves; but that would only rouse suspicion of Remus, whilst making sure the children had some idea of how to protect themselves if he proved dangerous. The Boggart would be much more damning, at least if it still resembled Remus. In any case, his decision to teach the class about werewolves came after he had very good reason to think that Remus was an enemy who was setting Harry up to be killed. Rightly or wrongly he clearly still regards Remus as dangerous, he saw Remus talking to Harry in private, then the very same night Sirius broke into the school and slashed the Fat Lady. Obviously Snape would assume Remus was setting Harry up to be killed by Sirius, just as Sirius had once set Snape himself up to be killed by Remus, and it was immediately after that that Snape dropped the hint about werewolves. Given what he thought was going on, it would have been immoral not to put the children on their guard. He, unlike Remus, is prepared to risk getting into trouble to protect the students.
[Also, Snape's decision to teach the class about werewolves came after Remus had encouraged Neville to make a laughing-stock of Snape in front of the class; so if Snape had actually backed out of the Boggart session in order to protect Remus he would be feeling understandably bitter and not at all inclined to go on protecting him.]
In fact, the only thing one can fault him on in this scene is in not being more blunt about what Remus was - but probably he still felt bound by his original promise to Dumbledore not to "out" Remus. There would be only nine or ten full moons during the school year, and any given student would only have two classes with Remus a week, so the chances of any particular student noticing that Remus's absences coincided with the full moon would not be high. That we know of, only Hermione worked it out - but since Snape thought that Remus was threatening Harry personally, it was enough that one of the Trio knew. Indeed, Hermione did warn Harry what Remus was, when she thought he was a threat.
As for his actually "outing" Remus at the end of term, I would suggest that his promise to Dumbledore, given all those years ago, had been that he would not reveal the fact that Remus was a werewolf unless he had firm evidence that Remus's condition was making him a threat to others. Suppose that you are a teacher at a real school. One of your colleagues is a violent schizophrenic. The Headmaster assures you that this colleague is perfectly safe so long as he takes his medication, but you discover that he has forgotten to take it, and has barely been prevented from killing three children. You also learn that even when he is in his right mind, the children's safety is not his highest priority, and that he will ignore his lack of medication even when reminded to take it.
Do you keep quiet and hope for the best, or do you warn the children that they are potentially in danger and need to treat this colleague with extreme caution?
Any belief that Snape acted out of spite towards Remus must be seen in the light of the fact that he later risked his own cover, and with it the whole course of the war against Voldemort, by firing on a Death Eater he thought was about to kill Remus - even if he did miss and cut George's ear off instead. If he did act partly out of spite when he shopped him, his spite is strictly limited in its scope, since he was prepared to take a risk to save him even after he'd been specifically ordered to do nothing which might jeopardize his cover.
Sirius complains near the beginning of OotP that Snape has been making "...snide hints that he's out there risking his life while I'm sat on my backside here having a nice comfortable time ... asking me how the cleaning's going --" We don't know which of them started it, although on other occasions Sirius is hostile first. With hindsight, knowing that Sirius left that hated house only to die, Snape's baiting of him looks terrible - but Snape had no way to know that was how things would turn out.
Sirius is the more overtly aggressive of the two, making unpleasant accusations against Snape, whereas Snape initially only teased him a bit. Sirius accuses Snape of planning to use the Occlumency lessons against Harry, of being an unreformed Death Eater, of being Lucius's lapdog.... Snape initially just says that Sirius finds not doing anything useful for the Order frustrating, and likes to feel involved - which is perfectly true, and not even insulting, although he says it to annoy. Snape is certainly no nastier to Sirius than Sirius is to him: it's just that Sirius is bluntly rude while Snape is delicately catty.
He doesn't say anything actively offensive - the suggestion that Sirius might have got himself seen in dog-form as an excuse to stay in hiding - until after Sirius calls him Lucius's lapdog. Quite how cruel Sirius was being depends on what the relationship between Lucius and Severus was and what Sirius knows about it, but certainly Sirius upped the conversational stakes first, and Snape only followed suit - just as Sirius drew his wand first, and Snape defended himself.
Snape is to Sirius as Harry is to Dudley. Both take pleasure in baiting their former tormentor; both try to save him when his life is endangered; both are afterwards unfairly blamed for having endangered him, when they were in fact trying to save him. The only difference is that Harry succeeded in saving his bully, whereas Snape failed; and the worst you can say is that Snape is twenty years older than Harry, and really ought to be a bit more mature than him.
Snape definitely did try to protect Sirius. Immediately after the fight at the Ministry, Dumbledore tells Harry that Snape had given Umbridge fake Veritaserum "when she was attempting to force you to tell her Sirius’s whereabouts." That event occurred the day after Dumbledore went into hiding. Harry has not told Dumbledore about it, he didn't mention it to Sirius and Remus and Dumbledore hasn't had a chance to speak to Snape yet since his return. [He wasn't at Grimmauld Place when Snape called there, and Snape asked Sirius to stay behind to brief Albus - clearly he hadn't had a chance to do so himself. And after the battle there wasn't time for Dumbledore to have spoken to anybody.]
So, the information about Snape giving Umbridge the fake Veritaserum and what she wanted it for must have come from Snape, during some private conference whilst Dumbledore was in hiding. Either Umbridge told Snape what she wanted it for, or he read it in her mind. He may have known, when he gave her the fake Veritaserum, that he was specifically protecting Sirius - and if he didn't know it then he knew it afterwards, and thought it important enough to warn Albus about. And he could very easily not have done. Only Umbridge knew that he knew she'd been fishing for information about Sirius. If Snape had been as callous about Sirius's life as Sirius was about his, he could simply have failed to warn the Order that Umbridge was making a push to catch him.
Snape undoubtedly has a vindictive streak, but his vindictiveness is strictly limited. He may want to prod his enemies with a metophorical stick and say "Nyahnyah - I won!" and enjoy seeing them do a slow burn about it, but he doesn't want to do anything messy.
We get to see exactly how vengeful and grudge-bearing Snape is. In the bullying scene, Peter is shown positively drooling over young!Snape's humiliation. Then Voldemort gives Peter - the man who, more than any other except Tom himself, is responsible for Lily's death - over into adult!Snape's hands; and he probably doesn't care that much what Snape does to him.
Snape is no angel, and he does take his revenge. But so far as we are shown, the sum of that revenge is that he sneers at Peter and makes him do the washing-up.
Even at his best, Snape is a bit spiteful.
Even at his worst, Snape is a bit spiteful.
When Snape takes points off the Trio for taking a library book (Quidditch Through the Ages) outside, you certainly get the impression he's invented that rule. But he'd just been bitten by Fluffy, and was limping noticeably, which suggests that he was in a lot of pain, and he does tend to deal with stress by giving it to other people.
In any case, the first page of the published version of Quidditch Through the Ages warns of awful consequences if the book is mistreated in any way, and Dumbledore's foreword speaks of Madame Pince adding unusual protective jinxes to library books, so it's entirely possible that Snape is telling the truth in this scene and there really is a rule about students (or perhaps just first-years) taking library books outside.
When Snape referees the Gryffindor/Hufflepuff match in PS, he awards a penalty to Hufflepuff because George has hit a Bludger at him, which is fair, but later he awards another penalty to Hufflepuff for, in Ron's opinion, no reason at all. At the end of the match, Harry nearly knocks Snape off his broom. Snape lands, white-faced and tight-lipped, and then is said to spit bitterly.
In PoA Remus claims that the enmity between Severus and James was because Severus was jealous of James's talent for Quidditch. We know it was mainly because James bullied Severus ragged, and later rivalry over Lily; but the fact that Remus chose that particular lie does suggest young!Snape was known not to be as good a flyer as James. Then, Harry sees Snape's memory of child!Snape failing to get onto a bucking broom, and in DH Snape tries to defend Remus by hexing a Death Eater whilst in mid-flight, and misses. Yet Snape has fast reflexes, he seems extremely observant and, as an adult, he moves in a way which suggests excellent coordination - all of which ought to have made him a potential Quidditch star. This, combined with his white face and tight lips after Harry nearly knocked him off his broom, suggests that Snape possibly suffers from vertigo, and that he spat because he'd just nearly been sick with fright or airsickness, and had a mouthful of stomach acid.
We know that by the end of DH Snape has learned to fly under his own power, but we don't know when he learned it. It could show that he longs for the freedom of the skies, or it could be a further indication of vertigo - he wants to ensure that if he falls, he won't hit the ground.
If, however, he really did spit from pure bitterness, he had something to be bitter about. As we later learn from Quirrelmort, in order to protect Harry Snape had put himself in a miserable position in the staff room, allowing the people he had to socialize with and eat with to think that he had insisted on refereeing the match in order to cheat, and making himself markedly unpopular. In return, Harry nearly knocked him off his broom accidentally, and George Weasley tried to do so deliberately.
We don't know whether he awarded a penalty to Hufflepuff for no reason (assuming that Ron was right about that) because he really was simply cheating; or because he needed Quirrel to think he was refereeing in order to cheat, to keep his protection of Harry secret; or because he didn't know the rules of Quidditch and was guessing wildly; or because he was so bitter about being sneered at in the staff-room when he was trying to do a good deed that he thought "Well, if you all think I'm going to cheat anyway, I might as well do the crime I'm being punished for."
If he really was spitting and not retching, that was an early clue that his origins were decidedly rough. Spitting in public is neither normal nor socially acceptable in Britain, except among teenage yobs and footballers.
At first glance, his behaviour at the Duelling Club, when he coaches Draco to use Serpensortia against Harry, seems strange or malicious. But we know he didn't intend to put Harry in danger, because protecting Harry is his raison d'etre. Harry already has spectacular reflexes and a record of dealing with dangerous problems, so there's a good chance he'll defeat the serpent - and if he doesn't, well, there's no reason why second-year Harry should look bad if he failed to deal with such an advanced spell (one which we will see Snape himself, and Voldemort, use in real combat). In other words, there's no reason why Snape should do this out of malice towards Harry, because it isn't something which would damage Harry.
It could be that Snape just wants to make Draco look good, or to show off his own ability in front of Lockhart when he deals with the serpent - or to demonstrate Lockhart's incompetence when he can't deal with it. But Snape is someone whose emotions usually show readily in his face, and his apparent lack of surprise when Harry speaks to the snake suggests that he set up the confrontation in order to test if Harry was a Parselmouth. It could be that Dumbledore - who already suspects that Harry is a Horcrux - told him to do so; or it could be that Snape came up with the idea himself, because he wanted to know if Harry could indeed be the Heir of Slytherin; or because he could sense something in him which smelled of the Dark Lord, even if he didn't know why.
In the scene in PoA where Snape interviews Harry about his appearance in Hogsmeade, and describes the Marauder's Map as Dark Magic, he seems to be being overbearing. He's certainly very angry, and he physically corners Harry and looms at him in his chair.
Snape, however, has good reason to be angry. He has seen Harry loitering suspiciously near the statue of the Hump-backed Witch, twice, and in between whiles he has evidence that Harry has been in Hogsmeade. His rant to Harry is not about Harry going to Hogsmeade without his guardians' permission, and not about Harry throwing things at Draco, but about Harry taking risks with his own person - and when he sees the parchment Harry is clutching he asks if it is a means of getting into Hogsmeade without passing the Dementors. Obviously his mind is running on ways that Sirius - whom he and everyone else believes to be a mass-murderer bent on killing Harry - might get into the school grounds and kill the boy.
'Is this another treasured gift from Mr Weasley? Or is it -- something else? A letter, perhaps, written in invisible ink? Or -- instructions to get into Hogsmeade without passing the Dementors?' [PoA Ch. #14 p. 211]
He seems a bit unfair, bringing Harry's father into it when Harry didn't even know his dad: but Draco's description of Harry's head appearing from nowhere ought to make an experienced wizard think "invisibility cloak" - and that may make him wonder if that was how James managed to stalk him so successfully, all those years ago. He's already thinking about Sirius and the danger he supposedly represents to Harry, so it's natural that his mind will dwell on James too.
Then the piece of parchment insults him, in personally-vicious terms. He may or may not recognise the nicknames on it: if he does he will have good reason to be upset, and good reason to suspect Lupin. He's already seen Lupin talking to Harry privately, and then that same night Sirius broke into the school with a knife. Now he wonders if the parchment is some kind of instructions to get Harry out of the school or Sirius into it, past the Dementors - and then it starts speaking using Lupin's nickname. He's bound to think both that this parchment, which answers the reader as if it had a mind of its own (or four minds), is a dangerous, Dark Magic lure meant to entice Harry into danger - just like the talking diary which lured Ginny to the Basilisk's lair only a few months ago, or Sirius who lured he himself to meet the werewolf - and that it may represent some sort of conspiracy between Remus and Sirius.
He's not that far off, either. Even Remus says that the Marauders would have lured Harry out of the school, just for a laugh, and the map is in fact a covert surveillance device which enables the user to spy on their schoolmates and teachers, and which is activated by swearing a solemn oath of wrongdoing.
In GoF there's a long-running side-plot about Snape planning to poison Harry in order to test an antidote. From the very beginning this sequence shows the depths of Harry's prejudice against Snape. Many of the teachers are setting the students a heavy workload, and Hagrid actually wants them to do homework on Skrewts three or four nights every week. Harry thinks of Hagrid as "suggesting" this extreme workload, but it is clear that it's not intended to be voluntary: when Draco doesn't want to take Hagrid up on his "suggestion" Hagrid tells him he'll do as he's told, humiliates him in front of the other students and makes him a laughingstock by reminding him of the ferret incident, and threatens him with an illegal punishment. Yet as far as Harry sees it, Hagrid has only "suggested" this compulsory extra work, Flitwick has "asked" for extra work, Binns "has them doing" extra work and Snape, and only Snape, has "forced" them to work. So we can assume from the outset that Harry is in a very prejudiced mood, and anything he thinks about Snape will probably be biased.
'Brilliant!' said Harry. 'It's Potions last thing on Friday! Snape won't have time to poison us all!' [GoF ch. #15 p. 207]
We see that already Harry thinks that Snape is planning to poison somebody in order to test an antidote, but Snape has merely "hinted". We don't know if Snape was serious or joking, or whether he was thinking about antidotes to poisons at that stage, or to e.g. Veritaserum or love potions. However, we do know that antidotes to poisons were covered that term, because Snape set a test on them.
A poison, in any case, need not be very bad. Anything which you ingest or inject or absorb or inhale, and which does you more harm than good, is a poison - even if it only makes you queasy or brings you out in a rash. We also see from the Swelling Solution incident in CoS that Snape keeps his own antidotes to hand in case of accidents, so if the student-brewed antidote being tested didn't work, there would be one available that did.
It proves to be true that Snape is planning to test an antidote on somebody (he says so, anyway), although the idea that he is planning to test the antidote against an actual poison, and on Harry, seems to rest only on Harry's own assumption. That whole dialogue in fact makes very little sense.
Snape says he wants Harry back "to test your antidote" - but Harry hasn't even started on brewing one, and probably won't have time to do so after his return, since there is only an hour of class-time left. Nor is Snape referring to a team effort by a team of which Harry is a member, because Hermione has fled to (presumably) the hospital wing with the overlarge teeth with which Draco had cursed her, and Ron is still not speaking to Harry, and is sitting with Seamus and Dean. Harry is working on his own, so unless he comes back very fast indeed there can be no "your antidote" in the sense of an antidote in whose brewing he has been involved.
Three possibilities suggest themselves. One is that Snape really does mean to test the antidote on Harry, and is saying "your antidote" in the sense in which people say "here's your coffee". But that would be a rather strange usage: since the object of the exercise is to test whether the person who brewed the antidote has done a good job, their "ownership" of the antidote is much more significant than Harry's as test-subject. If this is what Snape means it would be far more natural to say "...to test one of the antidotes."
There are two other possibilities, depending on what Snape means by "You should all have prepared your recipes". If he means that they have prepared in the sense of getting the ingredients out and ready, but that they are all working to the same recipe, then they are all attempting to brew the same antidote, and when he says he wants Harry present "to test your antidote" he may means the class as a whole's antidote. If so there's nothing definite to say that he necessarily wants to test it on Harry himself. Harry assumes so because Snape looks at him in a pointed way, but he may just want him to see it tested, to impress on this very sloppy student that correct brewing isn't just a classroom exercise but potentially a matter of life and death.
The other possibility is that "You should all have prepared your recipes" means that each student had worked out a recipe for themselves. In this case, Snape may be planning to get another student to make up Harry's recipe, or even to do it himself, to see how well it would turn out. Again there would be nothing definite to say that he necessarily means to test it on Harry - although he's probably amusing himself by deliberately making Harry think he does.
Harry never does make it back to the Potions class before it ends, and we never do find out whether Snape really did test an antidote on somebody, and in what sense, and what happened when he did - or whether he was just saying that to concentrate the class's minds.
At any rate, we can be sure he doesn't mean to do Harry any serious harm, because we know with hindsight that protecting Harry is his life's work. We can be pretty sure he's not planning to cause him serious pain, either, because during the chase which follows Dumbledore's death, Snape interrupts his own urgent flight to prevent one of the Death Eaters from Cruciating Harry. So if he is planning to poison Harry it will, indeed, be something of the nature of nausea, or a rash.
Nor is this particularly shocking, in the context of a school which allows students to fly fifty feet above the ground, and hosts a relative of Cerberus on the third floor. In the fanfiction Remember Him, or Penance by ThePet, Snape survives to be recognised for his valour after the war, and years down the line a Hogwarts student boasts proudly to a student from Beauxbatons: "And he poisons one of us every term just to make sure we're paying attention to the lessons on antidotes." This seems much more like how a real teenager would react. Harry is only horrified because he believes Snape really means to do him a real injury which, we now know, was certainly not the case.
The "I see no difference" crack about Hermione's teeth seems spiteful and childish, but he does have a massive grievance against her. She put Harry up to causing an explosion which inflicted similar distortions on several classmates, to create a distraction while she robbed Snape; and less than five months before the tooth incident she had thrown him into a wall and then left him to lie bleeding and unconscious for almost an hour. This remark, so far as we can tell, is his only retaliation. He then takes fifty points from Harry and Ron, where he normally takes points in fives and tens, which again suggests he may have been working off the grudge from the end of last term - or perhaps that he is in an especially vile mood because he has both Moody (as he thinks) and Karkaroff to contend with in the staff room.
It's not clear that he means it the way Harry and co. take it - that he can see no difference between Hermione's overgrown teeth and her usual ones - in any case. Since Ron is making a bit of a drama out of what's happened to Hermione, it's equally possible that Snape just means that Draco's having cursed Hermione is no worse than Harry's having cursed Goyle. [Here too we see that Snape doesn't condone bullying, because Pansy and the other Slytherin girls point and jeer at Hermione, but they do it in silence and behind Snape's back, so he won't catch them at it.] Or perhaps it just seemed like a good line. He would have to know Hermione much better than he does, to know that she was so sensitive about her large teeth - especially as he has irregular teeth himself, and evidently doesn't care enough about them to fix them.
When Snape blasted the courting couples out of the rose-bushes and took points from them after the Yule Ball in GoF, he seems like a spiteful killjoy. But Karkaroff had cornered him into a conversation which could get him killed if it was overheard by the wrong ears, and some of the students have Death Eater sympathies. Clearing the bushes of potential eavesdroppers was literally a matter of life or death.
Any consideration of how harsh Snape is must also take account of the fact that extreme physical punishment continued at Hogwarts well after McGonagall began working there (in 1956), and probably at least some years after Dumbledore took over as Headmaster (most likely in the early 1960s - see When was Albus Dumbledore appointed as Headmaster?).
We do not know how old Molly and Arthur are, except that Molly had left school before Snape and the Marauders started: we know that the Whomping Willow was planted the year Remus came to Hogwarts, and that that was after Molly had left. But their first child, Bill, was born circa 1970 (see Birthdates in the Harry Potter universe), and as they eloped and married as soon as they left school, and are demonstrably very fertile, they probably hadn't left school very long before Bill was born. So we can assume that they overlapped Dumbledore's Headmastership by at least several years, and probably didn't even start at Hogwarts until well after Minerva was appointed.
Whilst Arthur and Molly were at school, and old enough to be courting, they were caught sneaking around in the middle of the night together and Arthur was punished by Apollyon Pringle, the then caretaker, in some way that left him physically scarred for life. And he was probably beaten, or cursed, or whatever Pringle did to him, for courting, since the penalty for breaking curfew is not usually very severe. So Snape's somewhat killjoy attitude is official school policy, and far milder than past punishments for the same offence which probably took place on Dumbledore's watch.
Later in GoF, Snape threatens to dose Harry with Veritaserum on the sly in order to find out if Harry broke into his office. Clearly, this is some kind of dark joke: if he was actually going to do it, he would be mad to warn Harry in advance.
If he actually had dosed Harry with Veritaserum in the middle of the Great Hall in front of all his house-mates, though, as he threatened to do, it wouldn't have been particularly worse than Lupin making the whole class reveal their deepest fears to each other. In fact it would have worked to Harry's advantage, because then he could say both "I didn't raid your office" and "I didn't put my own name into the Cup", and be believed.
When Harry comes to tell Dumbledore that Barty Crouch Snr has been found in the Forest, rambling and mad, Snape emerges from Dumbledore's office and then behaves obstructively, telling Harry that the Headmaster is busy.
This seems irresponsible, but Dumbledore rapidly appears, and it may be that Snape knew that he would, and was just amusing himself rather spitefully by provoking Harry. "The Headmaster is busy" may well be a euphemism for "The Headmaster is taking a leak". Or perhaps Albus really was doing something which could not be interrupted.
Harry feels that Snape enjoys frustrating him while he is panicky, and the fact that Snape smiles tends to suggest that he is right, although he could be smiling over whatever Albus is busy with. But despite the hint of malice Snape is not really being any more obstructive to Harry than McGonagall is in PS, when Harry wants to warn the Headmaster that the Stone is in danger. However, having found a missing senior civil servant wandering deranged through the woods is a more urgent matter than some vague fear that the Stone might be stolen, and if Snape is being as obstructive as he sounds, this is one point where you could make a case for saying he was being truly irresponsible, and allowing spite to over-rule duty.
If Snape knew that the Headmaster would be down shortly, which he may well have done, he would know his snideness wouldn't delay the rescue-attempt, so he wasn't being obstructive: just petty. And initially, Harry just said Crouch was ill and wanted to see Dumbledore, which Snape may have seen as demanding arrogance on Crouch's part. We never find out how Snape would have reacted to the revelation that Crouch was mentally disturbed and wished to convey a warning, because Dumbledore arrived as soon as Harry had said it; if he hadn't, Snape might have gone to look for Crouch himself.
In any case, Snape probably has good reason to be reluctant to help Crouch Snr. Sirius said that towards the end of Vold War One Crouch authorized the use of Unforgivable Curses (plural, so not just Imperius) on Death Eater suspects, and became "as ruthless and cruel as many on the Dark side": which implies that those Unforgivables included Cruciatus.
Snape was a Death Eater suspect during that period. Dumbledore managed to get him off, but we don't know how long it took, and we see from the imprisonments of Hagrid and Stan Shunpike that Dumbledore's power to protect people from the Ministry is limited. It is quite possible that Snape was tortured on Crouch's orders.
Whether Snape himself was tortured or not, Crouch's policies must have added an extra distress to spying. Bad enough to hand over people who trusted him to be tried and then consigned to the Dementors; but to betray his erstwhile friends knowing that because of him they'd be tortured and imprisoned without trial, and possibly summarily executed, must have added another layer of miserable guilt to the guilt of the Potters' deaths.
Nevertheless, although Snape had reasons for his obstructive attitude that day, it contributed to the debacle at the Ministry a year later. It’s not surprizing that Harry didn't go to Snape when he "saw" Sirius being tortured, because his previous experience suggested that Snape would impede him.
Stopping the Occlumency lessons seems irresponsible, yet there are very strong reasons why Snape might feel he could not continue.
First off, Harry's hatred of Snape must have made reading his mind as unpleasant for Snape as for Harry. He was also distressed (white-faced and angry) at witnessing Cedric's murder, and shaken by having his own stressful childhood memories viewed.
Two days before that final Occlumency lesson, Dumbledore had fled the school to protect Harry. Dumbledore's presence is vital to Snape, because Snape's value to Voldemort depends on his continuing to be in a position to spy on Dumbledore.
One day before it, Snape had risked antagonizing Umbridge by supplying fake Veritaserum, to protect Harry and Harry's information about the Order; and a Slytherin disappeared. Shortly before he found Harry invading his memory that student had turned up with severe psychological and probably physical injuries. [If Montague was found in an actual toilet rather than a toilet-cubicle, which is unclear, he would have broken bones and internal damage; and we see that he still needs to be fed medicine with a spoon held by someone else, two months later.] Snape must have been crawling up the walls with stress.
Then he sees Harry - Harry for whose sake he is spending time on this lousy, stressful occupation, Harry who seldom bothers to practise even though he knows Voldemort may at any moment look out through his eyes, Harry for whose sake Dumbledore has had to flee the school - invading his memories. OK, he has invaded Harry's mind with every lesson, but he was doing it to protect Harry, whereas he thinks Harry is just being nosy. Snape reacts violently to Harry's invasion, just as Harry protected his memory of kissing Cho.
Snape knows that Harry has seen the miserable, scarring moment of his break-up with Lily, without even understanding that there was a friendship there to break up. He expects that Harry will have sided with James and enjoyed his humiliation, just as Lily turned on him and jeered at him; that Harry will snigger about it with his friends; that the nickname "Snivellus" will be resurrected. He must feel that the bullying and the rejection has never stopped and never will stop, that James is reaching down through Harry to continue tormenting him, and Lily is still turning on him and jeering at him through her son. He thought it had stopped, he thought he was over it, and now he's right back where he started. And if he didn't notice how far into the scene Harry had got, and the Marauders really did strip him, he may think that Harry has seen his genitals, in humiliating circumstances - so he feels sexually invaded, just as he must have done at the time.
There's also a security aspect. The other memories in the bowl might be things he didn't want Voldemort to see, through Harry - in which case the fact that Harry can't be trusted not to snoop could endanger Snape's life, and his usefulness to the Order. Indeed, the way in which Harry was suddenly gripped by a powerful urge to look in the Pensieve was rather suspicious, and it may actually have been Tom who prompted him to look. And Snape knows that his own nosiness killed Harry's parents, so he may feel especially angry to see Harry of all people taking stupid risks with information which might betray somebody to Voldemort.
As to the violence of Snape's reaction - I imagine if he'd actually intended the jar to hit Harry, it would have done.
Even before the revelations of DH, it was clear that Snape certainly was not treacherously using the lessons to make Harry more vulnerable to Voldemort. Dumbledore later tells Harry that he did not teach him Occlumency himself because "I was sure, at the time, that nothing could have been more dangerous than to open your mind even further to Voldemort while in my presence --" That is, a temporary widening of the channel between Harry and Voldemort was an expected part of learning Occlumency, and Albus thinks that it would have happened had he been teaching Harry, as much as it did with Snape.
After the fateful Occlumency lesson, there follows a Potions class during which Snape is so angry and distressed that he won't even look at Harry. Harry produces a good potion for once and takes a sample up to Snape's desk, but as he walks away he hears a crash behind him and turns to find his sample-bottle broken. Snape gives him a zero, and gloats about it.
If Snape deliberately knocked Harry's sample over that was deeply unprofessional of him, whatever the provocation - but there is no clear indication that Snape did so, or even that Harry thought he did. Neither Harry nor Hermione makes any comment to suggest that they think Snape broke it. All we have is Harry's thought about getting more and forcing Snape to mark it, which may just be a comment on the fact that Snape has been blanking him out.
The phial may well have been placed too near the edge (especially as Harry had a variety of reasons to feel more than ordinarily tense around Snape that day), or been knocked accidentally by Snape or by another student bringing their own sample to be marked, or by Harry himself as he turned away. We can say that Snape failed to prevent it from falling - but he had sunk into a kind of blank torpor of disgust relative to Harry, pretending that he did not exist, and dragging himself out of that in order to catch a toppling phial would have required a considerable mental wrench.
All we know for sure is that Snape did take a spiteful pleasure in Harry's misfortune - at a time when he was seeing him as a hateful extension of James. But since his attention was all on Harry at that moment, there's no reason why he should be aware that Hermione had Vanished the rest of Harry's potion. He would expect that he was just putting Harry to the nuisance of having to fetch more.
American readers should note, incidentally, that there appears to be no continuous assessment at Hogwarts: students' finishing grades, and career prospects, depend solely on how well they do in externally-administered exams, and on the references written for them by their head of house. Even if Snape did deliberately break Harry's phial, his action was purely nuisance-value: it would have no effect whatsoever on Harry's final marks.
When Snape meets Harry and Tonks at the gate at the start of HBP, he is rude to Tonks and brusque with Harry, who is said to be covered in blood. This is the only time we see him unconcerned about physical harm to a student, but he will probably assume it is just a nosebleed unless told otherwise. And he presumably knows that Auror Tonks will have First Aid knowledge and have fixed any immediate problems, and she says nothing to him to suggest that there is anything he needs to worry about.
Also, visibility was poor. Although Hermione comments later that Harry's face is covered in blood, she may be exaggerating, for we know that Harry made some attempt to wipe the blood off when he met Tonks at the station, and if he really had been horribly bloody you would think she would have Scourgified him. In the dark, if Harry wasn't looking directly at Snape because he hated him, and Snape was busy looking where he was going, he might not have noticed what a poor state Harry was in.
In any case, as an ex-Death Eater who works with explosives Snape is probably a bit numbed towards minor injuries, and a certain carelessness towards students' injuries seems to be a Hogwarts norm. In GoF, false!Moody threw ferret!Draco against a hard stone floor so hard that he bounced, several times, and was screaming with pain. Broken bones were very likely, internal injuries probable. McGonagall witnessed part of the attack, was troubled by it and called a halt to it - but she did nothing to check Draco for injuries, and did nothing to prevent his being roughly dragged away by the very man she had just seen abusing him. She didn't know false!Moody was a Death Eater, it's true: but she believed him to be an Auror who had served at a time when the Aurors were routinely torturing and killing suspects. And yet she let him roughly drag away a child he had just been brutalizing: despite the fact that as Deputy Head she should have had the authority to intervene. Evidently, at Hogwarts the physical and mental wellbeing of students is the concern of their head of house, only.
The best excuse for Minerva's failure to protect Draco is perhaps that she was so disturbed by "Moody's" behaviour that she was confused into paralysis and left thinking "Er - what just happened there?" That would be forgivable, although it doesn't say much for her qualities as either Order member or Deputy Head; both roles which require the ability to react fast and incisively, I would have thought. But if we allow that Minerva may neglect a student's well-being because she's been momentarily confused into acting like a stunned bunny, we must also allow that Snape may be nasty and unreasonable to Harry at the beginning of HBP because he's just been suddenly bounced out at by a huge Patronus which looked like were-Lupin, it gave him a horrible fright, and he's snarling to keep from shaking.
Regarding Snape's hostility to Harry in this scene, Draco may already have given a version of events on the train which put the blame solely on Harry, and at any rate the Patronus which Tonks intended for Hagrid may well have carried the information that Harry had been injured by Draco. He probably knows that in June Harry and the DA left Draco, Crabbe and Goyle to suffer for hours with severe curse-injuries on the same train, and that they did much the same the previous year; and, Draco being Draco, he won't know that Draco and co. started it by ambushing Harry three on one. If so, then if he sees that Harry is injured, he will think that Draco was the innocent party and that Harry's injuries serve him right. And if he knows or suspects that Harry spied on Draco he must fear Harry has jeopardized what he and Albus are planning re. the Vow and Draco's task.
His advice to Tonks, though snide, may be sincere. She is a junior Order member and a recent and able student (NEWT Potions is compulsory for Aurors, and to get into the NEWT class she presumably got an "Outstanding" at OWL) and he may really be concerned that her new Patronus is weak and could endanger her, or that Lupin the man is weak and not to be relied on - which, as we see in DH, is sound advice, although being Snape he probably does also get malicious pleasure out of sniping at Lupin.
Sionna_raven on Loose Canon suggests that what Snape means is that Tonks's Patronus is weak because it derives from her love for Remus, and her love for Remus isn't making her happy - her love for him isn't as self-sufficient and self-contained as Snape's love for Lily, she needs Remus to love her back and feels that he doesn't. Therefore her Patronus does not spring from very happy feelings, and therefore it will not be a good defence against Dementors. It may also be weak in the sense of being poorly formed, since Harry sees only a large four-legged shape: but that may just be because it went past him very fast. When Harry sees Dumbledore's Patronus in GoF, and Hermione sees Lupin's in PoA, there too they do not see them at all clearly.
Snape's manner to Tonks is rude (in contrast to the smoothie act he put on for Tonks's aunts), but he has reasons for his bad mood. He's been called away from his dinner, and from the Sorting Feast at which he should oversee his new Slytherins, and made to trail across the grounds in the dark because of Harry, who must seem like a constant aggravation. And he's been unexpectedly bounced out at by a Patronus in the form of were-Lupin, of whom he is terrified, and who reminds him of all sorts of angst-ridden memories involving Harry and James.
Also, as zgirnius has noted, Tonks has made it clear that she would rather have summoned Hagrid away from his important Sorting-night duties than speak to Snape, an Order member who was actually available. She may have felt that Hagrid would be free once he had finished with the first years, whereas Snape should be there to greet his new Slytherins; but depending on the history between them, he might well see her comment about intending to summon Hagrid as a slight, and he might be right to do so.
Depending on how he was treated when he was investigated in his early twenties, he may also have good reason to be bristlingly uncomfortable around Aurors generally.
When Snape speaks to Draco after Slughorn's Christmas party, he tries stiffly to pull rank, to get Draco to tell him what he's up to; but he does make an effort to be sympathetic about Lucius's imprisonment. Draco is quite nasty back, telling him to break his Vow - which literally means "Drop dead".
This could mean that Draco really dislikes Snape, but the writer Dyce makes a good case that Draco is letting off steam at an adult he knows is safe to shout at, like any fractious teenager screaming "I hate you, I wish you were dead!" at a parent or uncle. Either way, it's clear that Draco isn't afraid of Snape; neither as a man, a teacher nor a Death Eater. This again suggests that Death Eater!Snape doesn't have a particularly fierce reputation.
After Harry nearly kills Draco with Sectumsempra, Snape appears to read Harry's mind in a somewhat invasive way. But finding out where Harry got a dangerous spell from is an urgent, serious issue - considering that he has an established mental link to Voldemort. Snape would have to wonder whether the Dark Lord was influencing the boy again.
As a punishment, Snape makes Harry copy records of student misdeeds, including some committed by James and Sirius. Harry assumes Snape's motive is to upset him. McGonagall says Snape is being lenient and Harry could have been expelled (albeit Snape would hardly want Harry expelled when his own survival, and Tom's downfall, may rest on Harry's shoulders).
From Snape's viewpoint, Harry is another Sirius, killing for kicks; made worse because the victim is somebody he's probably known since infancy. Harry's hostile and self-righteous attitude will further convince him that Harry is like Sirius, attacking without compunction and stealing his spells to do it with, and he'll feel horribly guilty that his own spell injured Draco. We know that Harry's reaction to Draco's tears was neutral-to-pitying and his reaction to his injuries was horror and remorse, but Snape doesn't know that; and neither Harry nor Draco will tell him that Draco tried to Cruciate Harry, and Harry only lashed out in self-defence.
Seeing Harry apparently going the way Sirius went, it's reasonable for Snape to show Harry what poor rôle models James and Sirius were and how they spent their time on petty nastinesses (even Remus says James hexed people for fun). If Harry is right to think that Snape also takes a malicious pleasure in baiting Harry about the summer evenings which he is missing, that's not surprising: at this point he must really be seeing Harry as his own tormentors reborn, so he may be digging at Harry as Harry digs at Dudley.
It wouldn't occur to him that Harry really liked the boy in the book. With their past history he would see it as Harry stealing his spells and ideas the way James did - intruding into his private memories again, and then using his ideas to trick Slughorn into giving him better marks than he deserves.
We must consider that by this point, Snape believes that Dumbledore has groomed Harry to die, and has deceived him into thinking he was protecting Lily's son when really he was raising him like a pig to be slaughtered. In some respects that makes Snape's behaviour seem worse at this point, especially his apparent pleasure in keeping Harry appart from Ginny (although one can see that seeing the James-clone canoodling with his red-headed girlfriend would burn him). He knows Harry may well have only months to live, and yet he is depriving him of what may well be his only chance of romance.
But Snape is somebody who runs on stress and rage: he has to, to present a convincing front to Voldemort. He may well have whipped himself up into anger at Harry to numb himself from grief, and at any rate we know he was shocked and distressed to learn of the boy's probable fate, and now that he thinks Harry is a killer like Sirius he may well feel that he wasted his pain and his compunction on an unworthy object, and be the more resentful because of it.
[We also, of course, only have Harry's opinion that Snape is enjoying sabotaging his romance, and Harry may well be wrong. He certainly doesn't have hard evidence, since he only wonders if that's what Snape's doing, rather than being certain.]
On the rare occasions when we Snape relating to anybody outside Harry's class, we glimpse a reasonably pleasant persona. He doesn't often express emotion (except anger and bitterness) openly but his gestures are "tells": we see him clutch at the chair-back when he hears that Ginny has been taken, and whiten at Harry's memory of Cedric's death.
We know that he is, in fact, an emotional person, not a cold one: during both the Occlumency lessons and Slughorn's party we are explicitly shown that his cool, unemotional manner is a mask which he is putting on, and which can slip.
[cut] why was Snape looking at Malfoy as though both angry and ... was it possible? ... a little afraid? But almost before Harry had registered what he had seen [cut] Snape's face was smooothly inscrutable again. [HBP ch. #15; p. 300]
When we do see him express strong emotion, it is generally creditable. He goes to Dumbledore in terror for Lily's life (despite her harshness towards him), at a time when arrested Death Eater suspects are routinely being tortured and condemned to Azkaban without trial; yet his primary concern is Lily's danger, not his own, and he submits without complaint to being verbally abused by Dumbledore, and pledges his life to the man ("anything") without reserve. His grief when Lily dies is terrible, and apart from the initial comment that he had thought Dumbledore would keep Lily safe, we do not see a word of accusation concerning Dumbledore's failure to protect her adequately, even though Dumbledore is attacking him cruelly for putting his trust in Tom Riddle.
Despite having been a Death Eater he seems genuinely shocked by the expediancy which may see Harry sacrificed to win the war. Even his great rage against Sirius in PoA has creditable roots, though it leads him to be cruel and nearly causes a great injustice he doesn't intend. Apart from his personal grievance against Sirius (which is not an old grudge but an ongoing one, since he has just heard Sirius sneering about how he, Sirius, had nearly killed him), he believes Sirius to be a senior Death Eater who doomed Lily and who has spent thirteen years driven by a furious urge to finish the job by murdering her son.
He continues to love Lily, to the point of throwing over his allegiance to Voldemort and risking his life for her, even though she had dismissed him with what we are actually told was pitiless contempt. The strong feeling he still has for her in later life evidently is love, and not just guilt, because we've no reason to think a Patronus would take the form of somebody's self-blame.
He carries a grudge against the Marauders, but he has every reason to. It's not just something left over from his schooldays: Sirius still insults him at every turn and says that he deserved to be fed to a werewolf as a boy, Remus endangered the children under his care just to save face, and Peter betrayed Lily to her death, killed a dozen innocent bystanders in cold blood and resurrected Voldemort. Nevertheless, once Snape knows that Sirius isn't a mass-murdering Death Eater he tries to protect him, he risks blowing his own cover to protect Remus, and when Peter is in his power he limits himself to bullying him a bit.
[When he believes Sirius was the traitor who betrayed Lily, he seems to hate him far more than he does Peter when he knows Peter was the traitor. But he may believe Peter was terrorized into betraying the Potters, or that he was a very sincere Death Eater who truly believed that betraying them was a sad necessity to save Voldemort: whereas it would be difficult to attribute either cowardice or sincere political belief to Sirius. In any case this may be another way in which Severus is like Harry. Harry thinks he blames Snape for Sirius's death and hates him for it, but when he has Kreacher - who really did betray Sirius to death - in his power he does nothing to him except bully him slightly. In both cases, this may be because neither of them actually wants to be the sort of person who would hurt somebody who was in their power, however strong the reason might be.]
He sympathizes with Draco over his father's incarceration even in the midst of a flaming row, and when Draco is injured Snape not only heals him but pauses to wipe the blood from his face, and reassures him that he probably won't be scarred. He deals with Narcissa's tears awkwardly but quite kindly. He sneers at Bellatrix's suffering in Azkaban - but he may feel that as a sadistic torturer she has forfeited the right to sympathy, or that it's hypocritical of her to expect it.
He skulks uncomfortably around the edges of Slughorn's party, yet he does come - presumably out of obligation or affection for his old house-master. He even lets drunk!Sluggy put his arm round him, and doesn't recoil. In turn, at the meeting at the end of HBP Slughorn is the only member of staff to speak of his personal belief in Snape ("I thought I knew him") rather than some variant of "Albus trusted him and I trusted Albus".
There is a hint that Snape and Hagrid are friends. Hagrid is very reluctant to believe that Snape is a villain, and then in DH Snape "punishes" Neville, Ginny and Luna by sending them on a detention with Hagrid, and then puts it about that he had them horribly tortured - a deception which probably wouldn't work unless Hagrid was in on it. Aberforth, too, sounds as if he is referring to Snape when he talks about Albus using people, which suggests they too may be friends.
And Remus says "We shall never be bosom friends, perhaps; after all that happened between James and Sirius and Severus, there is too much bitterness there" - but he apparently doesn't see anything odd in the concept of Severus having bosom friends per se, nor even totally to rule it out for himself.
His relationship with Dumbledore is ambiguous. In the earlier books, Albus speaks as if they are friends, always calling him "Severus", inviting him to sample a custard-tart with him, speaking with sorrow of his unhealing emotional wounds. The scene at the Christmas table in PoA, where Snape pushes the vulture hat at Albus and Albus swaps with him, seems intimate and affectionate.
However, when we see them together in Snape's memories in DH Albus is often cruel to him, either deliberately or by accident. He blames Snape for having asked Voldemort to save Lily only, even though there was no possible excuse Snape could have given for asking Tom to spare Harry or James, and even though Albus himself then demands payment for saving them. He torments Snape with guilt over Lily when he is in the throes of great grief. He speaks coldly of the services Snape owes him, he manipulates his guilt and love for Lily to make him obey and continue to risk his life, and he conceals from him the fact that they may be raising Harry for slaughter - presumably because he knows Snape will be horrified. When Snape finds out and duly is horrified, Albus treats him and his ethical qualms like a specimen under a microscope.
Nevertheless, Snape's attitude to Dumbledore is quite warm. He tries to go behind his back to have Sirius executed, when he is raving with concussion and sincerely believes Sirius to be a mass-murderer and a senior Death Eater, but he backs off as soon as he realizes Albus was involved in Sirius's escape. If the vulture hat in the Christmas cracker was Albus's doing (which it probably wasn't), he takes it in good part, and he fusses over Albus like a nanny when he is injured.
That we see, he only balks at Albus's orders twice: once when he risks his cover to protect Lupin, despite having been told not to, and once when he is reluctant to kill Albus. And the lever Albus uses to make him obey is an appeal to his mercy, his compassion for a dying friend. Altogether, Snape treats Albus much better than Albus treats him.
His relationship with Minerva is similarly uncertain. In the earlier books, she speaks of their rivalry, how she couldn't look Snape in the eye for weeks after his team flattened hers, and she says "Professor Dumbledore" but she says "Severus Snape", and the whole thing sounds more like affectionate winding-each-other-up than bitter competition.
After Dumbledore is killed, it is not the news of his death which causes Minerva to nearly faint, but the news that it was Snape who killed him. Yet, she readily believes that he murdered Albus, she says at the end of HBP that she had always wondered about his true loyalties and had only trusted him on Albus's say-so, and in the end she turns against him and drives him out with great harshness, without apparently asking herself why he would have kept two Order members on the staff if he was Tom's man. It's not clear whether she had always hated and distrusted him, and the appearance of affectionate rivalry was misleading, or whether she had been fond of him, and felt the more betrayed and the more angry because of it when she thought he had deceived her. The fact that she nearly faints when she learns that it was Snape who killed Dumbledore slightly suggests the latter.
Either way, we know Snape hates to be called a coward and hates to be jeered at, and yet he flees, inviting Minerva's scorn, rather than defend himself and fire on her. For all his verbal harshness and his spiteful streak, Snape serves Minerva a lot better than she serves him - as he does likewise with Albus, with Lily, with the Marauders, with Draco and with Harry. Like Harry, he may snarl and snap at people he has good reason to resent, but when the proverbial chips are down he pays back good for evil and protects the very people who have ill-treated him.
Some fanwriters think Snape has no sense of humour, but if you "get" sarcasm you see that Snape is joking most of the time. Sarcasm is highly regarded in Britain, and is generally neither intended nor taken as seriously as it would be in a society where sarcasm is rare.
Indeed, sarcasm is common among the Hogwarts staff - McGonagall, Dumbledore and Flitwick all use it. Consider Dumbledore's comment that "[Scrimgeour] is not very happy with me, either. We must try not to sink beneath our anguish, Harry, but battle on." When the staff confront Lockhart after Ginny has been taken, Snape, with his not-so-subtle needling, speaks for all of them. He and Dumbledore and McGonagall and Flitwick probably sit around drinking coffee and bitching about people they don't like.
Snape doesn't seem able to laugh at himself, however, at least in front of students, although there may be an element of self-sendup in all that dramatic prowling and robe-swishing, and in his teasing of McGonagall. But around the children, he is too defensive to let his guard down.
That he is so sensitive about being laughed at, and stands so much on his dignity, is hardly surprising. We see that he grew up as a poor boy from a rough home, from a family sneered at even by other people from the same area ("You're that Snape boy!" Petunia says, and we're told her tone is scathing), dressed by his parents in ridiculous, effeminate hand-me-downs which must have made him a laughing-stock. It's a virtual certainty that he was bullied at Muggle school, unless he defended himself so fiercely he drove the bullies off.
Then he was bullied at Hogwarts, in a vicious way which involved public, quasi-sexual humiliation, and then had to teach children not much younger than himself, some of whom probably witnessed that humiliation and most of whom will certainly have known about it. It's not surprising that he is still red-raw, yet he submits to being ostracised and sneered at in the staff room, for Harry's sake and, during his final year, to protect the children in general.
Indeed, you can interpret Snape's story-arc as a journey from the needy little boy who was desperate for a friend, to the teenager who clung to one group of friends and so lost another, the young man who (interview canon) joined an extremist group because he was desperate to belong, the grown man who gave up his friendships and his standing among his colleagues in order to protect the son of his first friend, all the way to the grim Headmaster who embraced near-total loneliness and isolation and gave up even the slim warmth of protecting his ex-friend's son, in order to do what was right. And the author was merciful and gave him a moment of connection, a breach in his loneliness as he lay dying, because even though Harry still thought Snape was an enemy he is basically a kind boy, when he remembers to be.
Snape is no more sarcastic than Dumbledore, not much nastier to Neville than McGonagall is and probably no more prone to playing favourites than Hagrid is. He only seems extra-nasty because he doesn't like Harry, and it's through Harry's eyes that we see him. Ironically Snape and Harry have much in common, and we see, through the Prince's book, that Harry would have liked Severus if they'd met as boys.
Snape behaves to Sirius as Harry behaves to Dudley - enjoying baiting a former tormentor, but still trying to save his life. Snape plasters on a sickly smile to congratulate McGonagall for winning the House Cup in PS, and Harry does the same over Ron's Prefect's badge.
Each turns from someone else's strong emotion in a fit of masculine embarrassment, described in exactly the same way. "[Snape] looked away from the sight of [Narcissa's] tears as though they were indecent". "Harry had never seen Lupin lose control before, he felt as though he was intruding upon something private, indecent; he turned away".
They also resemble each other in wanting to blame somebody else. I suspect Snape wanted Sirius to be guilty so he could blame him for the Potters' deaths, instead of himself. And Harry obsessively blames Snape for Sirius's death, which he half knows is unfair - but it's less painful than blaming himself, and less dangerous than blaming Kreacher, whom he actually could hurt.
No doubt some people still think Snape must have been essentially selfish, despite his love for Lily, because he was a Slytherin; especially as Phineas said that given the choice, Slytherins always choose to save their own necks, and he sounds like The Voice of the Author here. But so does Firenze sound like The Voice of the Author when he gives the message that Hagrid's attempt to communicate with Grawp isn't working and should be abandoned, and yet he turns out to be wrong. Phineas's opinion is just Phineas's opinion, and in fact most of the Slytherins we see are brave and self-sacrificing - even if not always for a worthy object. Bellatrix's deranged love for Tom Riddle is still love.
To be Sorted into Slytherin means that ambition is your most striking characteristic, not that you don't have the other house attributes of courage, loyalty and intellectual passion as well, and ambition may as easily be selfless as selfish - there must be Slytherins whose ambition is to find a cure for dragon-pox, or write the great wizarding novel. The difference between them and Gryffindors is that Gryffindors have a sort of Viking zeitgeist which encourages them to be brashly brave for the sake of proving how brave they are, whereas Slytherins are brave to achieve an object. The war-cry for the final battle was "Brave Regulus!", and even Horace ended up duelling Tom in his green silk pyjamas.
Snape is, in his snarly way, more consciously ethical than most of the "nice" characters. When he did something very wrong he had the moral, emotional and physical courage to go to Dumbledore and confess, at the risk of ending up in Azkaban or being killed by Voldemort. This contrasts markedly with Sirius, still sulkily trying to justify his attempt to murder a classmate for kicks, and Lupin, who preferred to leave Harry in danger from a supposed mass-murderer rather than admit that he had broken Dumbledore's trust as a boy.
He feels intense remorse for Lily's death, even though he hadn't known whom he was betraying, and had risked his life to save her. There's no suggestion that he makes excuses for himself, even though there are excuses which can be made. If Dumbledore is to be believed, he also feels himself in debt to James - and Dumbledore lied by omission in that scene, by leaving Lily out of it, but he also promised Harry that everything he did say would be true, so there's a reasonable chance that it is.
We know now that James went right on bullying Severus after he saved him, so Snape is right to suspect he acted to protect Sirius and Remus, not out of any concern for him. He has no reason to think James would have lifted a finger to save him otherwise. And although he was partly responsible for James's death he did try to save him, it was the fortunes of war, and James was in part the architect of his own fate, for trusting the Marauders too blindly. That Snape nevertheless feels - according to Dumbledore - that he is in James's debt shows how sensitive he is to such matters.
He appears to loathe teaching, yet does it dutifully, and doesn't skimp on his work. Altogether he has a degree of moral seriousness which is lacking from most of the other characters, and is always taking risks for other people: even if he is a bit of a drama queen who probably quite enjoys being the covert, under-appreciated heroic martyr.
One of the few other characters who seems to think about ethics (along with Hermione and Albus) is Sirius, who talks about how the world is much more complicated than just "them and us". But he has, as JKR herself has commented, a complete blind spot about Snape.
Canon Snape seems to be non-violent to a degree remarkable in a former Death Eater, or in anybody as seething with pain and resentment as he seems to be. His outbursts of physical violence are very rare, very mild and happen only when he is raw with distress and humiliation, or to protect others.
He drops a branch on Petunia in an outburst of wandless magic when she jeers at the humiliating clothes his family dress him in, but we're shown no evidence that it was anything other than accidental, like Harry's vanishing of the glass barrier at the zoo. He gives James a small, controlled magical cut when James publicly attacks and humiliates him without provocation. He seizes Harry roughly by the arm and shoves him aside when he finds him viewing his misery in the Pensieve (and throws a jar after him, but I'm sure if he'd meant it actually to hit Harry, it would have done). He gives Harry the magical equivalent of a slap when Harry calls him a coward - as opposed to Remus, who throws Harry against the wall for the same offence. He hacks at a Death Eater to protect Remus. That is all the physical aggression we see from him, and only dragging Harry away from the Pensieve involves actual hands-on physical contact, which probably lasted less than ten seconds.
Nor do we ever see him be emotionally manipulative - the closest he comes to it is saying "I thought we were friends" to Lily. He's a terrible nagger and inclined to gloat, but even his verbal aggression is straightforward, and although there's quite a lot of it it's not especially nasty, especially compared with the verbal cruelty we see being directed against him. He doesn't even seem to know how to manipulate people when it would be an obviously sensible thing to do: Remus exerts far more controlling influence over Harry by telling him he's being disrespectful of his parents' sacrifice than Snape does by his confrontational approach.
As regards authorial intent, JK Rowling at interview has called Snape cruel and a bully, but since she also called the Twins cruel we do not know if she means any more than that Snape has a slightly nasty sense of humour, as the Twins do. From what we see in the text, Snape is more overbearing towards the students than he perhaps should be, but he certainly isn't a bully in the classic sense of someone who picks on the weak while fawning on the strong: he's abrasive to just about everybody except Tom Riddle, whom he is stitching up. It's not a case of him picking on the weak specifically, but of failing to temper his abrasive attitude to make allowances for the weak - possibly because he hasn't really internalised the fact that he has power over anybody else, since he grew up so much at the bottom of the heap.
Much has been made of the fact that when an American interviewer called Snape a hero JKR initially said that she didn't see him as a hero, although she later said that he was one, or perhaps an anti-hero. This caused a lot of argument, but it seems pretty clear that she was simply suffering from linguistic confusion.
In Britain, the word "hero" nowadays is most commonly used to mean "rôle model", rather than "person who acts heroically". For example, on 7th August 2008 it was reported in the Daily Mail (a fairly right-wing British tabloid which is serious-minded, as tabloids go, and aimed mainly at a middle-aged and older readership), that Prime Minister Gordon Brown had named Scott of the Antarctic as his hero, and the reporter commented: "His journey is the stuff of legend. But given his cold and lonely death, Captain Scott is unlikely to be a character many would seek to emulate. // However, for Gordon Brown, the ill-fated explorer is a hero."
We also see the Guardian (a very serious left-wing broadsheet) using the term "hero" to describe the admiration which children feel for the footballer David Beckham, who has never done anything especially heroic, but who is considered a "hero" because he combines his footballing career with being an attentive father. That is, both a right-wing tabloid and a left-wing broadsheet, both serious-minded papers, use "hero" as a synonym for "rôle model", to the point that the Mail is actually surprised that anybody would choose, as a hero, a person who performed heroic deeds but whose manner of death was a tragic one which most people would not wish to emulate.
The reasons JKR initially gave for saying that she did not see Snape as a hero were relevant to whether or not he was a good rôle model, but not relevant to whether or not he behaved heroically. Therefore, it seems virtually certain that she didn't mean that Snape was not heroic: she had simply understood "Is he a hero?" to mean "Is he a good rôle model?", because that's what it usually means in Britain.
Nor does her later calling him an anti-hero mean that she thinks he was not heroic. In British usage, an anti-hero is not a person who is the antithesis of heroism, but a person who is heroic but who is also dark or dodgy in some way.
JK also said (in a LiveChat on 30th July 2007) that Harry would make sure Snape's heroism [her word] was known, and that Rita Skeeter would write a book called Snape: Scoundrel or Saint? Generally in those sort of either/or titles, it is the second one which is the true thrust of the book: when we hear that Rita wrote a biography called Armando Dippet: Master or Moron? we are in no doubt that her conclusion was "moron". The implication therefore is that Rita will write a biography which concludes that Snape was a saint. And since JK portrays Rita as somebody whose major stories generally have some truth in them, even if that truth gets badly distorted, presumably JK thinks there is a case to be made for Snape being a saint, even if that's an exaggeration.
A discussion in the Leaky Lounge reportedly concluded that Snape was a sexual sadist. We know that he isn't a sadist in the psychopathic sense, because if he was he wouldn't have spent however-long-it-was as a Death Eater without attracting the slightest attention. As to whether he might be a mutual-game-playing, S&M-type sadist, I discussed this with someone who knows a lot of S&Mers, and his immediate response was that Snape was absolutely not the type.
His reasons were that Snape is too self-conscious and walled-off for that sort of complex two-way emotional dance, isn't "physical" enough, and since he spends his working life in complex and terrifying rôle-playing he's not likely to want to do it in private as well: quite the reverse. He's far more likely to want a straightforward roll in the hay, or wine and candlelight and a soft bed, than something kinky with whips and chains.
Speaking personally, I especially don't buy Dominatrix!Snape or Control-freak!Snape. People who want that sort of control over others generally seem to do so to compensate for their own inability to control themselves or their lives, or from insecurity. The fact that Snape has survived so long as a spy shows he has very good control over himself, and although he serves two demanding masters he also holds the fate of the wizarding world in his hands. Whilst his situation is insecure, it's a sort of professional insecurity which he knows how to cope with, rather than an underlying neurosis. He can be a bit overbearing towards the children, but isn't especially controlling, and his behaviour towards Peter when Peter is in his power again suggests a moderate degree of bossiness, rather than an urge really to control.
A submissive Snape - whilst still unlikely, given his abrasive and argumentative nature - is slightly more feasible. We do at least see, from his history with Tobias, Tom and Albus, that he is probably seeking for a father-figure, and is resigned to that father-figure being abusive. And he has led a life full of miserable, crushing responsibilities, and might find it a relief to hand that responsibility over to someone else for a while.
The same friend, who is bisexual and has a well-developed "gaydar", also said incidentally that in his expert opinion canon!Snape is about as obviously straight as it is possible for a fictional character to be. There's no sense that he ever checks another man out - no sense that he ever even considers the handsome Lockhart as a sexual prospect (not even to conclude "Ew, no thanks!") or has any reaction to being embraced by Horace other than "This is my friend; my friend is very drunk". Conversely, there is a faint but definite sense of frisson between Snape and Narcissa.
[Harry, on the other hand, is almost certainly bi, since he is excessively aware of how other males look, and assesses them in terms of their attractiveness.]
There is a strange little half-comic, half-numinous book called The Wee Book of Calvin by Bill Duncan which may be instructive in understanding Snape's personality-type. We've no particular reason to think Snape is a Calvinist in the literal, religious sense, and indeed I personally have written him as a lapsed Catholic (mainly because of his Spanish-looking and decidely un-British colouring), but many of the Calvinist attitudes which Duncan describes are common in northern England as a sort of general cultural background. Read ARE YOU A CALVINIST? for what seems a likely insight into Snape's emotional landscape.
We know now, of course, that Snape was definitely following Dumbledore's orders when he killed him; and we can also be virtually certain that Dumbledore had already given him this order before he took the Unbreakable Vow.
Both events - Dumbledore's injury, followed within the hour by his decision that Snape would have to kill him, and the taking of the Unbreakable Vow - occurred between the fight at the Ministry of Magic in mid June 1996 and Dumbledore's collecting Harry from the Dursleys in mid July 1996, by which point Dumbledore already had a withered hand. The Spinner's End chapter takes place in July (Snape refers to the Dumbledore/Voldemort duel at the climax of the Ministry battle as having occurred "last month"), some time prior to Dumbledore collecting Harry.
In the Spinner's End scene, Snape refers to a serious injury which Dumbledore has sustained since the Ministry of Magic fight. Since it is most unlikely that Dumbledore would have sustained two serious injuries in one month, one of which we aren't told about, we must assume Snape is talking about the curse-injury to Dumbledore's hand, and that this is after Dumbledore arranged his own death with Snape.
Dumbledore certainly already knows, on the night he puts on the Peverell ring and sustains the curse injury, that Draco has been ordered to kill him, and he discusses it with Snape, who presumably told him about it in the first place. So Snape knew what he was swearing to when he took the Vow, and he also knew that it was what Dumbledore wanted. His flinching jerk of the hand when Narcissa asks him to carry out Draco's task if Draco should fail, then, must spring from reluctance to obey Dumbledore's order - or perhaps he has been thinking of refusing to kill the old man, and realises that now if he does refuse, he himself will die.
We do not know whether Snape ever tells Dumbledore about the Vow. When Harry tells Dumbledore that Snape has taken an Unbreakable Vow to protect Draco, Dumbledore implies that he already knows, and there is no nefarious reason why Snape would fail to tell him. It's not as if he's biding his time, preparing to sneak up on Dumbledore unexpectedly in order to save himself: Dumbledore wants him to kill him. And yet, when they argue about it in the Forest, Dumbledore reminds Snape of his promise to him, of "services you owe me": he does not say "You know that unless either yourself or Draco kills me, your own life will be forfeit".
This suggests one of two things. One is that Snape has not told Dumbledore about the bit of the Vow where he swore to carry out Draco's mission if Draco failed. Under the circumstances there seems no good reason why he wouldn't tell him, unless it is that he is still hoping to get out of killing the old man, at the probable cost of his own life, and doesn't want to hand Dumbledore another arguing-point.
The other is that Dumbledore does know about it, but he doesn't use it as an argument because he knows Snape regards his own life as of little importance. Either way, we know about the Vow, and we know Snape is trying to get out of killing Dumbledore - so we know he is willing to die for the old man, or in order not to be a killer.
At the Astronomy Tower we see Dumbledore actually plead with Snape. It could be that he is faking it in order to make his supposed murder look more convincing, but if he really is pleading then he fears that Snape will still refuse to kill him at the last moment. If he knows about the third clause of Snape's Vow, then he thinks that Snape will choose to die to buy him a few more weeks of life - and he certainly believes Snape is very reluctant to kill.
We also see that Snape is concerned that killing might damage his soul, so he certainly isn't a killer now. Probably he never was - or if he ever was, he desperately doesn't want to repeat it. He is not a particularly ruthless man now, and probably he never was.
It was necessary for Snape to kill Dumbledore, or at least they thought it was: and not just for humanitarian reasons. Dumbledore believed that the curse which was on the Peverell ring was placed there by Tom when he put his Horcrux into it ("I quite forgot that it was now a Horcrux, that the ring was sure to carry a curse"), so if he allowed himself to die of that curse, it would be Tom who had killed him, and so the mastery of the Elder Wand would go to Tom, which he desperately wanted to avoid. Even if he committed suicide, he would be doing it because of the curse, and so there would be a risk that it would still count as Tom having defeated him.
Getting Harry to feed him poison may have been insurance: if Snape refused at the last minute to kill him, then his blood would be on Harry's hands and either Harry would get the mastery, or it would die with him because he had ordered his own death. He couldn't know for certain, in advance, how the Wand would interpret a death he himself had ordered, so he arranged matters so that if the mastery didn't die with him, it would go to Snape, or failing him, to Harry.
In the event, of course, it went to Draco, so Snape's killing Dumbledore didn't make a difference to the disposition of the wand: but there wasn't time to rethink their plans, and by that point, in any case, Albus really was in a position where he might be killed slowly and horribly, and really needed the mercy he had asked Severus for.
To anyone who still hates Snape for killing Albus, even though it was on Albus's orders, consider this. An hour or so beforehand, on the man's own orders, Harry force-fed Albus the potion from the Eldritch Birdbath of Doom. This certainly contributed to Albus's death, by making him too weak to defend himself.
If Snape had not killed Dumbledore, and Albus had died some hours later from the poison which Harry made him drink, would you transfer your hatred from Snape to Harry? If not, why not?
As to why Snape stared at the Headmaster in apparent hatred and revulsion - we know he was not a natural killer, so he would have hated what he was having to do. He also had much to resent the old man for, for we see that Albus was sometimes very cruel to him - and also he'd be angry with Albus for emotionally-blackmailing him into doing something he didn't want to do. This is Snape we're talking about, after all - and nobody ever claimed he had an easy temperament.
But if the fact that he is capable of hating Albus is a moral fault, then the same must apply to Harry - for here, too, they mirror each other. At the end of OotP, Harry too feels violent hatred towards Albus for his implacable calm when Harry has just lost a beloved father-figure, but Snape has been commanded to be the author of his own bereavement.
We know Snape spent his dying breaths (assuming he really was dead and not just unconscious) still doing his duty and giving Harry the information he needed to complete his task - and also to show him the truth of his friendship with Lily. It's ambiguous whether that final "Look at me" was a plea for Harry to let him die gazing at Lily's eyes, or for Harry (or Lily-in-Harry) finally to see him as he truly was.
The fact that the memories he gave to Harry included the information that he had been trying to protect Remus when he cut George's ear does suggest that he cared about what Harry (or perhaps Remus) thought of him, and wanted somebody to understand that he wasn't at all the cold-hearted bastard they often thought him. It wasn't just to explain why he had injured an Order member, in order to get Harry to trust him. The memory of portrait!Albus telling him that if he became embroiled in the chase he would have to make it look convincing would do that, and could easily be verified by asking Albus. Nothing was changed by the revelation that Snape had disobeyed Dumbledore and risked his cover to save Remus - except his reputation in Harry's eyes and those of his former colleagues.
Similarly, he didn't really need to give Harry those memories of Lily, from a practical point of view. He needs to make Harry trust him but it would probably have been enough to show Harry Dumbledore ordering his own death, and discussing the Horcrux in Harry and why Harry too had to die. The information that he was friends with Lily - and in such detail, showing their childhood conversations and quarrels - has little practical benefit, but it makes a memorial for those children and that friendship, it lays bare both Snape's love and what he feels to be his fault, and makes Harry a final gift of his mother's memory, echoing the photographic book of memories which Hagrid prepares for Harry in the first book.
Was his death itself sacrificial? Did he have a choice about whether he died or not, or only about how he conducted himself in death?
When his colleagues attack him and drive him out, he responds to their attacks effectively and with lightning swiftness, but all his moves are defensive ones and he does nothing to harm them even when they are throwing knives at him. Presumably, then, his reason for fleeing is because he doesn't want to hurt them, not because he is unable to fight back, so he is already making a sacrifice: exiling himself and sending himself out to stand among the Death Eaters who are in fact his enemies, rather than hurt the people who used to be his friends.
He can't come right out and tell them he's on their side, of course, even if they would believe him - which they almost certainly wouldn't. If Voldemort won, Snape would have to stay on at Hogwarts to protect the children, so he can't reveal his true allegiance to people whose minds are vulnerable to Legilimency.
When we see Snape with Voldemort in the Shack, he is still trying to do his duty and get to Harry to give him Dumbledore's message. Initially he seems tense but calm, but we see him become progressively more nervous as the conversation continues. He begins to stutter slightly when Tom says that the Wand is not performing any remarkable acts for him, and he turns deathly-white when Tom begins to talk about it by name as the Elder Wand. JKR seems to be deliberately showing us that the mention of the Elder Wand, or the demonstration that Voldemort knew what it was, had special significance to him and frightened him especially. Did Snape then understand the situation with the Wand?
Dumbledore tends not to tell anybody anything if he can help it. Nevertheless, it seems clear that he wanted Snape to learn about Horcruxes, or to be reminded about them. Whether as Dark wizard or DADA teacher Snape certainly has the reputation of being academically interested in Dark Magic, and Dumbledore left a stack of Dark Magic grimoires with sections on Horcruxes in them in his office, which he knew would soon be Snape's office. He couldn't have known in advance that Hermione would steal them, and he must have known that if they were still there when Snape took over Snape would read them - so he must have wanted him to.
Why did Dumbledore want Snape to think about Horcruxes, and yet wouldn't tell him about them himself? He said himself that he was wary of entrusting secrets to somebody who spent so much time so close to Voldemort. Presumably, therefore, he didn't want to tell Snape about the multiple Horcruxes himself because he didn't want the risk of Voldemort breaking through into Snape's true mind and finding out that he, Dumbledore, knew about the multiple Horcruxes. That would be dangerous for the cause and absolutely fatal for Snape, since there could be no reason for his failure to pass on the fact that Dumbledore knew such an important and (to Tom) threatening thing, other than his true loyalty to Dumbledore. On the other hand, if Tom saw in Snape's mind that Snape had read a book about Horcruxes and had speculated about them in relation to Tom, with no apparent reason to think Dumbledore had reached the same conclusion, there would be nothing suspicious about his failure to raise the matter.
To some extent it would be dangerous for Snape if Tom found out that Dumbledore had told him that Tom couldn't die while Harry lived, and Snape hadn't passed it on - but he could at least say "But master, I knew, because you told us so, that you had taken other steps to make yourself immortal and that you would still live even if Potter died." In any case, he may have passed that information on - it would explain why Tom had ordered the Death Eaters to leave Harry for him. But Tom, too, would think that he was safe to kill Harry, because he had other Horcruxes and to the best of his knowledge, Dumbledore didn't know about them. Even in the final battle, he probably still thought the diadem was safe.
So, we can see that Dumbledore apparently did want to keep Snape informed, where it was useful to the anti-Voldemort cause for him to be informed, and where his being informed would not unduly endanger either the cause or Snape himself.
Although Harry tells Voldemort that Dumbledore expected the mastery of the Elder Wand to die with him, what he says to Dumbledore is that Dumbledore expected the wand to "end up" with Snape, and Dumbledore agrees with that. It does not sound as if they are talking about mere physical possession of a stick - especially as they are discussing it in the context of Dumbledore and Snape making mutual plans - and at any rate Dumbledore couldn't know in advance whether ordering Severus to kill him would cause the mastery to die with him, or to go to Severus.
If there was a good chance of Snape ending up with the mastery of the Wand, then you would think that he would be much better equipped to make informed choices about it, and therefore to be as useful to the cause as he potentially could be, if he actually knew about it. Since there is evidence that Dumbledore did want to keep Snape informed, where it was both useful and safe to do so, he would probably want to tell him about the Wand - if it was safe to do so.
Was it safe? Well, so far as we see Tom Riddle did not begin to take an interest in the Elder Wand until after Dumbledore's death, so they had no reason to think that the Dark Lord would specifically probe Snape for information about Dumbeldore's wand (as it were). In the other hand, if Dumbledore told Snape about the Wand weeks or months before his death and Voldemort for some reason chose to interrogate him, there was a risk he would find out Snape was keeping this vital secret from him.
However, although Dumbledore could not have known the exact day of his death, he did know he would die by the end of term. So long as he told Snape towards the end of term the risk of Snape being caught concealing information by Tom in the short time remaining would be low. Once Dumbledore was dead, if Draco had not intervened the mastery of the Wand would either have died with Dumbledore or passed to Snape. If it died with Dumbledore, Snape had the perfect excuse for not having told his master about a weapon which no longer existed anyway. If it passed to Snape, the danger from Tom would be much less anyway, because Snape now had an unbeatable weapon. So there was no very strong reason not to tell him.
Of course, even if Albus did intend to tell him about the wand he may have died before he had the chance to do so - but then portrtait!Albus could have told him about it later. By that point, however, he would know that the mastery had gone to Draco, so telling Snape about it would put him in at least some danger, since he was concealing the existence of a dangerous weapon from Tom, without himself being protected by it.
Even if Albus deemed it too risky to tell Snape about the Wand while Tom did not know about it, once it became apparent that Tom had broken into his tomb - which happened about a month before Snape's death - then it would be both advisable and safe for portrait!Albus to explain what was going on, so Snape would be forwarned. And even if neither he nor portrait!Albus knew that the Wand had been retrieved and buried with Albus, once the tomb was broken into they would have reason to find out, and to surmise that that was what Tom had been after.
Once Snape had reason to think Tom already knew that Dumbledore's wand was the Deathstick, he couldn’t be accused of keeping the identity of the Wand a secret. In which case, it was safe for him and Dumbledore to discuss the disposition of the mastery. It shouldn’t matter that Dumbledore had asked him to kill him, or whether or not he had told Tom about that, or that Dumbledore had thought the mastery of the Wand would go to him, because Voldemort knows that Dumbledore thinks Snape is Dumbledore’s man. All Snape has to say is "The old fool thought that I was killing him on his own orders but really I killed him for you my lord: I was merely a weapon in your hand, and the mastery should have come to you." Depending on how intelligent and responsive the Wand is, if Snape truly had the mastery then it might actually work for Tom well enough to fool him, if Snape wished it to do so and doing so served Snape's interests.
Knowing the mastery had probably passed to Draco, and not telling Tom about it, would still be risky, but Snape could at least say "I did not tell you because if I exposed him to your wrath I would have broken my Vow to protect him, and I would die, and besides my lord I thought you knew that Draco had disarmed him." Tom would not be happy about that, but at least it wouldn't make Snape a traitor and it wouldn't be as bad as not having told him the Wand even existed, so he might get away with it. The risk, at any rate, would probably be less than the risk which would arise from not knowing what was going on, once Tom actually had his hands on a weapon that wasn't going to work for him.
From the way Snape is described as being especially white and scared when Voldemort talks about the Deathstick, it does look as if JKR means us to understand that he knows what Tom is talking about and knows that this topic is dangerous to him personally: and I have shown that it is perfectly possible, even quite likely that he does know. If so he had at least a month to think through all the ramifications, and may have had a year. And in that case, Snape could have saved himself, or at least tried to - but he chose not to.
If Snape knows anything about the mastery of the Wand, he knows that it didn't go to him - unless he thinks Dumbledore had simply dropped it, but he's probably heard what really happened from Draco, or from Dumbledore's portrait. So he knows the mastery went initially to Draco, although he may or may not know what happened to it next.
He can't say "Draco has the mastery of the Wand", because then Tom would seek out Draco with a view to killing him - and Snape has taken an Unbreakable Vow to protect Draco as best he can. But it's clear Tom doesn't know the details of what happened on the Astronomy Tower, so Snape could perfectly well say that Dumbledore was disarmed by the Death Eater who was later killed in the fight, and that the mastery went to whoever killed him. It might or might not work, but it would have at least a chance of working long enough to buy him time, and one way or another Snape has had a year to think up a good excuse - so why doesn't he even attempt it?
Snape may or may not know that the mastery has gone to Harry, but he knows (if he knows anything about it at all) that he doesn't have it, and that if Voldemort thinks he can get the mastery by killing him, Voldemort is wrong. Presumably, then, if he knows what's going on - as his whitening at that particular point suggests - he chooses to keep silent and let Voldemort kill him, rather than warn Lily's murderer that he is about to go into battle with a weapon which will not answer to him. This would explain why Rowling said that Snape laid down his life because of love - which sounds likes something a lot more intentional and controlled than simply gambling on whether or not Voldemort would kill him, and losing.
It is no longer necessary, as it was in the earlier version of this essay, to provide evidence of Snape's true allegiance to the anti-Voldemort cause. We know now that he was, very literally, faithful unto death. To what extent, though, were his good actions driven solely by his love of and guilt over Lily, and to what extent was he moved by wider considerations? Was he (despite his temper, his sourness etc.) a good and intrinsically loving person - or just an obsessive one?
Snape is not an emotionless person, nor is he lacking in fear. When he defects to Dumbledore we see him utterly terrified by his own situation and Lily's. He turns white when Harry nearly knocks him off his broom, and again when he has to return to Voldemort, and he is sheet-white and stammering as he confronts his own death. Yet he still returns to danger, again and again, to do what he thinks is right.
Snape hates Sirius, and he has every reason to - yet when Sirius is unconscious, Snape summons a stretcher for him. He believes that Sirius is a mass-murdering Death Eater who is responsible for Lily's death, and he sincerely wants him worse than dead in return - yet when it comes to it he, unlike Sirius, cannot bring himself to be rough with an unconscious prisoner.
Later, even when he knows Sirius wasn't a traitor, it remains true that Sirius is a bully and a would-be murderer who tormented him as a boy, who tried to kill him and who remains unrepentant about it. Yet when Snape finds out that Umbridge is investigating Sirius, Snape takes the trouble to warn Dumbledore (as we know he did, because Dumbledore knows about it at a point at which his information could only have come from Snape).
Snape's position under Umbridge is a precarious one. He could easily lose his job - and if he did, he would also lose most of his usefulness to Voldemort, especially if Dumbledore were not reinstated. Yet Snape incurs her wrath by messing her around over supplying Veritaserum. That to some extent protects Harry as well as Sirius. But there is no benefit to Lily's son, or to the cause, when Snape, already on probation, risks angering Umbridge further by intervening to prevent Crabbe from throttling Neville.
He has a sincere grievance against Remus, who took part in persecuting him as a boy, and undermined him as an adult. He had no qualms about getting Remus sacked once it was evident that the man really was a danger to students. Yet when he thought Remus's life was in immediate danger, he risked blowing his cover in order to protect him - even though doing so ran contrary to Lily's interests, and those of the Order. As with Sirius, when he sees someone in danger his gut instinct is protective, even if it's an enemy. And he cares that people should know that - or perhaps that George should know he didn't injure him deliberately - so much that he includes it in his dying testimony to Harry.
He likewise risks drawing the Carrows' suspicion down on himself by giving Neville, Ginny and Luna a detention which is more of a reward, after they try to steal Godric's sword. His motives are, perhaps, always personal - he is moved by concern for individuals, rather than by any wider political picture. But he shows concern for all individuals, not just for Lily and her son, and he fights Voldemort because Voldemort is something from whom individuals need to be protected.
We see this when Dumbledore reminds him of his promise to stay and protect the school - even though that is not the course of action which best serves Harry. We see it when he says that since he ceased to be a true Death Eater, he has only watched people die if he could not save them - that is, he saves the Death Eaters' victims where he can, even though doing so does not serve Lily's interests, and risks blowing his cover.
We also see it when he runs through the castle in his nightshirt because he heard somebody scream, even though he didn't know (until he got there) that Harry was in any way involved; and when he sprinted through a closed bathroom door, not knowing who or what might be on the other side and probably again not knowing that Harry was involved, or anything except that a girl's voice had screamed "Murder!"
We know, also, that his dedication to Dumbledore and the Order is sincere, even if it centres around his loyalty to Lily, and even if Dumbledore to some extent emotionally manipulates him into it. It cannot be the case, as some people have suggested, that he has to obey Dumbledore because he is in the old man's power: from the point at which Dumbledore let Snape know that he had connived at Sirius's escape, if not before, Snape had far more serious blackmail material on Dumbledore than vice versa. We have plenty of evidence that he had never been a very enthusiastic Death Eater, and the Ministry had already pardoned his past and rubber-stamped it, so there are no dark secrets in his past that Dumbledore didn't order him to: but he knew all manner of interesting things about Dumbledore and the Order which the Ministry would have loved to know. The fact that Dumbledore was nevertheless so offhand with him shows how deeply he trusted him - and his trust was not misplaced.
It isn't simply that Snape will protect the people under his care from danger of death: he will protect them from pain if he can, despite his own sometimes spiteful nature. It is noteworthy that the lever which Albus uses to persuade Snape to kill him is not political strategy but an appeal to his innate mercy - that Snape should give him the quick, painless death which the man himself can hardly hope for.
In the scene where Harry pursued Snape and the Death Eaters across the grounds after Dumbledore's death, the reason which Snape gave for stopping one of the Death Eaters from Cruciating Harry was clearly bogus. It might be true that Voldemort wanted to deal with Harry himself, but there was no reason why the Death Eaters shouldn't have their nasty fun, without killing him. But Snape took the trouble and the risk of protecting Harry from suffering, not just from danger - even though he himself ended up giving Harry the magical equivalent of a slap for calling him a coward (which is rather less violent than the hex which Remus throws at Harry in DH for calling him the same, btw).
And then, as Snape fled, Buckbeak tore at him, and Snape did nothing to defend himself. Even if he hadn't the energy for another Avada Kedavra you would think he would be able to do something to drop a flying predator the size of a horse which was trying to maul him, but he does nothing. Just as he would not fire on Minerva and Filius even when they were trying to kill him, so he was apparently willing to let himself be mauled, rather than either harm an innocent animal or upset Hagrid by hurting his pet.
And then, in the end, Snape does as Dumbledore tells him, and gives Harry the information which he thinks will send the boy to his death. We know he does so most unwillingly - we see his shock and anger in the Pensieve - so he doesn't act out of carelessness for Harry's safety, whether he likes the boy or not. It must be because he has been persuaded that Dumbledore is right. He began by pledging anything and, by implication, everything to Dumbledore and the Order for Lily's sake, and ended by giving up even his dedication to Lily's memory, for Dumbledore's and the Order's sakes.
So here we have our man - stressed-out, ill-tempered, sarcastic and harsh, sometimes childish and often spiteful but also brave, protective, ethical, dutiful and self-sacrificing. He's certainly no angel - but his virtues compare well with the best that the light side has to offer, and his faults are arguably less than those of many other "good" characters. Being a bit petty and spiteful hardly compares with trying to murder someone for kicks, or covering up information which could save a child's life, just to save face.
Ultimately, the story pivots on him. Without Snape's loving devotion to a friend who had rejected him, his willingness to risk everything to plead with the Dark Lord for her life, Tom Riddle would never have offered Lily the choice of whether to live or die, and there would have been no Blood Protection, no sudden disembodiment of Voldemort, no Harry. Of course, if Snape had never relayed the prophecy in the first place the Potters wouldn't have been singled out, although they would still have been in danger as Order members: but whether Tom had pursued them and killed them all, or ignored them altogether, without Snape's intervention, and Lily's willing sacrifice which flowed from it, the Death Eaters would have swept to victory in the 1980s, and wizarding Britain would have been ground under the heel of an immortal dictator.
Without Snape's devotion and courage, his willingness to spend his last few seconds of life passing on the instructions which would enable Harry to win the war, Harry might still have lost the final battle. "The Flaw in the Plan" which brought Voldemort down, and which was the final chapter-title and the culmination of the series, was Snape's capacity for love and sacrifice, and Voldemort's failure to anticipate it. Even Harry's signature Expelliarmus, which carried him to victory, is a spell he learned from Snape.
I once characterized Snape to the writer duj as "Doing the Right Thing with exemplary courage whilst bitching about it the whole way" - to which she replied "That's our Snape, all right".
