Memory and the Past Quotes in Harry Potter and the Prisoner of Azkaban
How we cite our quotes: Chapter.Paragraph or Chapter.Section.Paragraph (depends on whether or not the chapter had sections - some did not)
"And how do you conjure it?"
"With an incantation, which will work only if you are concentrating, with all your might, on a single, very happy memory." (12.3.11-12)
While the past is often bad in this book, Harry does have happy memories too. It's rather poetic that, to produce a Patronus, you have to focus on the good times even while surrounded by darkness.
Terrible though it was to hear his parents' last moments replayed inside his head, these were the only times Harry had heard their voices since he was a very small child. But he'd never be able to produce a proper Patronus if he half wanted to hear his parents again [...] (12.3.76)
Poor orphan Harry – we feel a lot of sympathy for our hero here. This passage emphasizes how long it's been since Harry has heard his parents' voices. It's fitting that he can't produce a Patronus (i.e., create a spell that depends on having a strong happy feeling) while he's clinging to his tragic past.
"Oh no," said Lupin. "Much worse than that. You can exist without your soul, you know, as long as your brain and heart are still working. But you'll have no sense of self anymore, no memory, no [...] anything. There's no chance at all of recovery. You'll just – exist. As an empty shell." (12.5.22)
The Dementors are like some sort of existential nightmare come to life – they can force people to wander around as empty shells, "existing" physically but not mentally. It's significant that Lupin points out "memory" as a key component to the "self." Even though dwelling on or obsessing over the past is a bad idea, no one should deny or totally forget what came before. It's a tricky balance that Harry has trouble with the entire novel.