Throughout the history of the world, many people have written on various topics in a language of their choice. They write in either prose or poetry. A small fraction of it is pretty to hear. The parts we like, we call literature. Perhaps one of the best methods of determining whether a given work is "literary" is to determine how many layers of meaning the work has - compare a Danielle Steel novel (one superficial layer of meaning) to any of Shakespeare's plays (three, four, twenty layers of meaning) - or the quantity of directions from which one may approach the work for interpretive purposes (which "coincidentally" often depends on layers of meaning). The broadest definitions of literature include works beyond the "traditional" scope - consisting of novels, short stories, novellas, poems, and plays - to include music, graphic novels, and other such artistic productions.
Before Plato and Aristotle, scientific treatises were expected to be written in highly metered poetry. In Plato's dialogues, Socrates constantly promises to finish a few but never does.
"Literary criticism is usually itself considered a form of literature."
 Literary theories
Myriad literary theories exist, but most employ some variation of the scientific method (or can be argued to do so) in the process of analysis. Some of the more common modern examples include:
- Psychoanalytic (Jungian or Freudian/Lacanian)
- Queer theory
 Literary criticism
This exists in many forms, from the "reasonable" (as considered by most outside observers) to the totally meaningless. Typical of the latter is a story often attributed to Isaac Asimov, wherein he argues that a teacher is misunderstanding a piece of his, to which responds the teacher: "Just because you wrote it, what makes you think you have the slightest idea what it's about?"
Much literary criticism involves one idea spread over 500 pages, looking for examples of feminism/patriarchism/queerness/colonialist oppression/class struggle and oppression/(add examples to taste) in statements taken out of context, and, at the same time, explaining why the theories of other members of literary establishments are #totally wrong#. The overlap with woo is variable.
Then again, there are some acolytes like Harold Bloom or Helen Vendler (who both studied sciences) who find this approach pretentious, or worse, pseudo-scientific. They advocate instead the enjoyment literature as an end in itself, and their theory-oriented colleagues as attempting to find a neo-moralist approach to literature. Interestingly enough, their books tend to be deprived of jargon and fun to read in themselves.
Jorge Luis Borges coyly suggested that all religions are, in fact derived from "fantastic tales". In 1790 the admirably crazy William Blake defined religion as "choosing forms of worship based on Poetic Tales". In America, Walt Whitman first titled Leaves of Grass as The New Bible. If you're interested in how religions work... *hint hint nudge nudge*
A good deal of literature has a good amount of grounding in scientific and mathematical subjects. These include
- Douglas Adams-Writer of the Hitchhiker's series. Friend of Dawkins. Heavy on fiction, but still fun.
- Edwin Abbott Abbott-Writer of Flatland, a novel using complicated mathematical concepts to satirize manners and society.
- The works of Lewis Carroll-Not just for kids, massively entertaining and contain many many relevant logical puzzles.
- George Gamow-A physicist and friend of Einstein who wrote novels and humorous verse bringing both physics and its problems down to a conversational level.
- Terry Pratchett-Writer of the Discworld series. Probably one of the best fictionalizers of modern Moral problems we have.