/lit/ - Literature

Would it be incredibly pretentious of me to throw in random passages from poems and other literature into a novel I'm writing?Like, if a character were reciting a poem, could I just include a part of or the whole thing? Can I have my characters quote long passages and short phrases from prose tracts as if from memory, have them burst into song, or even just include this stuff and imply that they are the characters' thoughts, or perhaps even have the narrator intrude upon the text and sum up the scene with a pretty phrase stolen from Keats or Manley Hopkins?
I'm reading Joyce Cary's The Horse's Mouth and the protagonist is an unapologetic con-artist/genius painter and he'll just randomly insert passages from Blake ranging from a few lines thrown into the dialogue to him reciting entire short poems, there's even a passage from the Prophetic Books thrown in. I know inter-textuality is a thing, Sebald does it a lot in The Rings of Saturn, Emerson quotes other poets as much as himself, Thoreau talks about ancient greeks and wild squirrels in the same breath; but, is it possible to do this now?