In the firstHarry Pottermovie -The Sorcerer’s Stone, Harry asks Percy about the teacher seated across the Great Hall at the High Table. The latter informs him he’s the Potions Master, and head of Slytherin House, Severus Snape. Percy says Snape fancies the Dark Arts and has been after the post for years. In Snape’s first Potions lesson with Harry’s class, he makes it clear that his subject is superior to the “foolish wand-waving or silly incantations” bit that they have been practicing so far. He thinks of Potions as subtle science and exact art that can be used to bewitch the mind and ensnare the senses. While Snape clearly loves the subject he’s been tasked to teach, a lifelong fascination with the Dark Arts is one of the defining aspects of thisHarry Pottercharacter.
Chapter 33 ofHarry Potter and the Deathly Hallows"The Prince’s Tale," is a fantastic insight into Snape’s budding years at Hogwarts. Right off the bat, on Hogwarts Express, he declares he wants to be sorted into Slytherin, as he prefers being brainy over brawny. Later as a Slytherin, he is friends with Avery and Mulciber who use Dark Magic. When they attack a student named Mary MacDonald with Dark Magic, Snape excuses it as “nothing” and “a laugh.” A while after, Snape, set in his ways, doesn’t deny to his best friend and the love of his life, Lily Evans that he wants to be a Death Eater. A Hogwarts graduate, he does, in fact, become one of Voldemort’s loyalists and relays Sybill Trelawney’s partial prophecy to him.Snape shifts allegianceonly after the Dark Lord marked Lily (and James) Potter for death and left their infant behind.

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Snape And The Dark Arts
Snape liked to dabble in the Dark Arts as a student. In chapter 27 ofHarry Potter and the Goblet of Fire"Padfoot Returns," Sirius Black reveals to Harry that Snape was known for his fascination with the Dark Arts and that he knew more curses when he arrived at Hogwarts than half the kids in their seventh year. At school, he associated with the gang of Slytherins, nearly all of whom turned out to be Death Eaters. Chapter 33 ofHarry Potter and the Deathly Hallows"The Prince’s Tale," reveals that Dumbledore toldSnape about Voldemort’s returnand showed him the way forward. Snape wanted the Defense Against the Dark Arts job simply because he excelled at it. He was the good side’s best candidate to prepare Hogwarts students for the real world and the future predicament.
In chapter 2 ofHarry Potter and the Half-Blood Prince"Spinner’s End," Snape reveals that Dumbledore denied him the Defense Against the Dark Arts job because he seemed to think the position would bring about a relapse and tempt him into his old ways. Another reason why Dumbledore did so was to protect him from the said position. In Chapter 20 ofHarry Potter and the Half-BloodPrince “Lord Voldemort’s Request,” Dumbledore revealed that Hogwarts had not been able to keep any Defense Against the Dark Arts teacher for longer than a year since herefused it to Lord Voldemort.

Snape Takes On The Defense Against The Dark Arts Position
Snape’s first Defense Against the Dark Arts lesson takes place when the Trio is in their sixth year at Hogwarts, in Chapter 9 ofHarry Potter and the Half-Blood Prince. This titular chapter speaks of him creating a gloomy ambiance before proceeding to deliver a few words about taking up the mantle. “Snape had imposed his personality upon the room already; it was gloomier than usual as curtains had been drawn over the windows, and was lit by candlelight,” the chapter states. The pictures that adorned the walls were those of people in pain, injured, or of their body parts twisted out of shape. Theopening words of Professor Snape’s address, “‘You have had five teachers in this subject so far, I believe,” agitated Harry as they were an understatement of how his teacher felt towards the former D.A.D.A. teachers. The boy knew Snape watched them come and go hoping he’d be next.
In the titular chapter ofHarry Potter and the Half-Blood Prince, Snape passionately declares the Dark Arts “…are many, varied, ever-changing and eternal.” He explains the defense against the Dark Arts means “…fighting a many-headed monster, which, each time a neck is severed, sprouts a head even fiercer and cleverer than before.” Simply put, according to Snape, fighting against the Dark Arts meant fighting the “unfixed, mutating, indestructible.” While Snape was speaking about his favorite subject, Harry stared at him in disbelief. To him, respecting the Dark Arts as a formidable enemy and speaking about them ever-so-lovingly were two different things.
That being said, Snape’s passionate address made it clear that aimed for his students to excel. He spoke about the Cruciatus Curse, the Dementors' kiss, and the aggression of the Inferius. When Parvati Patil asked if Inferius has been seen at all, Snape informed her the Dark Lord did indeed use Inferi in the past, and they wouldn’t be wrong to assume he might use them again. Snape, in a nutshell, wanted the coveted position to prepare his students for their N.E.W.T.s. He taught them to assume the worst of the Dark Lord. His subject began with non-verbal spells, divided the students into pairs, with one attempting to jinx their partner without speaking, and the other attempting to repel this jinx in silence. But of course, Snape being Snape, slapped Harry with detention, told Hermione off, and called Ron’s attempt to jinx Harry “pathetic.” While certainly not the friendliest, Snape was among the most capableDefense Against the Dark Arts professorsinHarry Potter.
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