Why Canon Supports Snape's Involvement with Lily: A Surface Analysis

Snape brought the prophesy to You-Know-Who

And he went to Dumbledore soon after it. Dumbledore says, 'you have no idea of the remorse Professor Snape felt when he realised how Lord Voldemort had interpreted the prophecy, Harry. I believe it to be the greatest regret of his life and the reason that he returned'. Why is this? It's certainly not because he feels any sympathy for how it has influenced Harry's life, and Voldemort was intent on genocide far before the prophesy. Why does Snape suddenly have a change of heart when the Dark Lord specifically turns his sights on Lily and her family?

Something had to turn Snape back to Dumbledore, and the event happened directly after the Potter's became (again, specifically) involved. Why would the killing of his old school rival have caused him to turn? No, it was Lily's death which ultimately brought back the humanity in Snape.

Never, once, does anyone say Snape hated Harry's mother

He and James loathed each other, but why stop the abuse there? Draco repeatedly insults both of Harry's parents throughout the series. In book 5 Harry 'takes a go' at Seamus' mother, proving that others are not sacrosanct in canon. Lily was a Gryffindor, one who married James, why else would Snape stop short of bringing her into his taunts at Harry?

Repeatedly we hear about the rivalry and the hatred between James and Severus. From the first book Snape insults Harry's father, and in OotP we see that his feelings were mutual: James purposely antagonised him as well, without provocation.

Sirius too seems to have hated him, but not as much as James is made out to, and we know that Remus--even before Snape brews him the Wolfsbane potion--does not share the same hatred of Snape that his friends did. Sirius is the one who was regarded as most loyal to James, Remus less so. Thus it makes sense that Sirius, the one who grew up to despise anything to do with his Slytherin upbringing, and who was also rather more unforgiving than Remus, is the one who stood by James in his animosity toward Snape.

Snape often heaps abuse on Harry, simply for being James' son, but he never faults him for being Lily's.

Snape is always mean to Harry

This hardly needs addressing. Certainly Harry is Lily's son, but he is also James' something which Snape is always quick to point out. Harry is the product of James and Lily's happy (if short) time together. Looking at Harry, Snape is reminded that he lost Lily to James, his love to his bitter rival. Harry's existence also caused Lily's death. For Harry to live, Lily had to die, something Snape can never forgive him for, even though it was hardly Harry's fault. It, of course, was Voldemort's. Something which addressed in the first point.

Snape called Lily a Mudblood

This scene is actually what convinced me that there was something going on between Lily and Snape.

Why would James pick Severus to bait out of a whole gang of Slytherins. We've seen the average intelligence of stock Slytherin characters. Why would James pick someone who had an extensive knowledge of the dark arts to taunt? We know Snape is attacked unprovoked because Lily asks, 'what's he done to you?' implying that James has no legitimate reason to hate Snape. Except, of course, jealousy. There must have been some incident in the past over Lily which caused James to be jealous of Snape.

Then Lily comes to Snape's rescue. Even if she hates James, why argue for the release of a Slytherin? Why risk having to talk to James Potter if it's over someone she didn't care about, whom she knew would be ungrateful?

Snape and Lily actually work together to get him free. Lily yells at James, trying to negotiate Severus' release, while Snape inches toward his wand, unnoticed. When Snape fires back at James, Lily's 'furious expression [...] twitched for an instant as though she was going to smile'. While this is written after Snape is showing off his underpants,

She even turns her wand on the Marauders, and keeps repeating, 'leave him alone' usually yelling when she says it, and always emphasising the word, 'alone'.

Snape may seem ungrateful, but when he spits out his abuse of Lily--which he absolutely must do, to keep up any façade and to be accepted in Slytherin at all--he aims his words at James, not Lily. He doesn't turn to her and say, 'I don't need your help, you Mudblood bitch,' he doesn't even look at her. Just as any proud, teenager couldn't bear to look at their girlfriend while humiliated at being in such a vulnerable position.

After Severus acts out his part, Lily plays hers. After Severus' remark, she blinks. Her eyes don't narrow, she doesn't hiss, 'go to hell' at him. She does tell him he should, 'wash his pants' but the cold remark she makes is far from the 'furious' way she acts toward James, nor does she, 'look at him with great dislike' the way she does James. To Snape, Lily responds 'coolly' going on to tell James she doesn't want Snape to give her an apology.

Now, is that a normal response after a hostile remark? Why did Lily not get as furious with Snape as she did with James if they had no (at least somewhat friendly) connection? They must have planned for this sort of situation in advance, and maybe were even used to it. If they were hiding a relationship of any sort: platonic or romantic, they knew they would have to hide it from the school. They couldn't be seen being civil to each other, and Lily risked their cover by coming to his rescue.

Petunia mentions a boy Lily knew (who was probably not James)

In Book 5 we hear Petunia say about dementors that she heard, '...that awful boy telling her...'. Not 'your father,' but, 'that awful boy'. Admittedly this could be a stretch, but logically it is not all that farfetched. JKR is usually only vague when there is something to hide, and Harry's desperate cry that immediately follows for his aunt to, 'use [his mum and dad's] names' is pushing an ambiguous situation that seemingly has no other purpose. Why would JKR waste these two lines on Harry's response if they had no importance? Surely wouldn't she have had Petunia say, 'I heard that awful father of yours...' or 'that Potter boy' as she had previously called him?

Now that we have determined the line to be significant by not referring to James, we must examine whether or not she meant Snape. Who else could she have meant? Obviously a wizard, given the circumstances, and someone who was the same age as Lily, due to her use of the word, 'boy' which she would not have used to describe Dumbledore. From what we know of Sirius he was rather dashing, and there is no conceivable reason she should describe him as 'awful' while Remus and Peter seem innocuous enough not to be referred to by that term either. This leaves Snape, who, as we know, had a significant knowledge of the dark arts.

Lily was good at Potions

So far it seems that most characters in this book do not share the same talents in school subjects. Hagrid has a penchant for (Care of) Magical Creatures, Neville Herbology, Lupin Defense Against the Dark Arts, Lavender (somewhat) Divination, James Transfiguration, and so on. So why does JKR chose Potions of all things for Lily? A subject that we have associated so closely with Snape over the course of five previous books?

JKR makes a point in telling us of Lily's particular talent in Potions. She purposely brought back a professor who had taught Lily. It is canonically important to know that Slughorn taught You Know Who, but what reason is there for him to have still been around while Harry's parents were in school? Some may argue that it allowed for Harry's newfound talent in Potions to be more believable, but since any professor teaching the course would be new to the skill levels of his students, there is no reason for the person who came to teach be the same as the one who taught James, Severus and Lily.

Also important, is the fact that Slughorn repeatedly praises Lily as his star pupil over Severus. We know from Harry's use of his old textbook that Snape was talented at Potions. Yet, it is always Lily whom he attributes this to. Slughorn never mentions that Harry's talent might have come in part from Snape's teaching over the past years. Since Snape never seems to want to come in second to anyone, he must have taken an intense interest in Lily, if she was beating him--or coming close to it--in class. As promising young students with a shared talent, they would have been thrown together quite often, especially since we have seen that Slughorn 'rewards' his students with invitations to the 'Slug Club'.