Originally Posted by The Joker
"You didn't think I'd risk losing the battle for Gotham's soul in a fist fight with you. Noooo, you need an ace in the hole. Mine's Harvey"
"I'll show you, when the chips are down these civilized people, they'll eat each other"
Joker's philosophy is his motive. Just as Ra's philosophy about justice and balance was his motive.
His multiple choice origin story is the nod to the comics where Joker is so insane that he remembers his past differently.
Well, I would agree that if we had to put a motive on The Joker, it would be his philosophy. I just don't like to think of it that way. That's like saying Batman's motive to do what he does is to stop crime and defend Gotham because its citizens are basically good and deserve saving. Yes, it's technically kind of true but it misses the full scope of why
he chooses to do it in the particular way that he does it. I feel there's something inherently "unknowable" about The Joker's evil and that's part of his lasting appeal as a character, and that's why they included that nod to The Killing Joke in TDK. All of the villains in this series have a philosophy. But we don't get to know a single thing about where The Joker came from like we do with Two-Face, Bane, Ra's and Talia. We know what his worldview is, but not what shaped it or how it came to be. Same with Crane. We know how he views fear and its power over the mind, but not what caused him to be like that. With The Joker we don't even know why he went with the clown motif. It just is...and that's awesome.