Hoo boy — I’d have to be insane to try to define theory. It’s a blanket term that covers many kinds of approaches to literature, language, and culture. Although it can refer to almost any kind of careful consideration of these things — Aristotle, after all, was a fine literary theorist — in practice theory usually means the kinds of approaches that became common, at least in the Anglo-American world, beginning in the late 1960s.
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See also deconstruction, feminism, and structuralism.
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.