Literature - Any form of written storytelling
So let me walk through my thinking here. In much the same way that art can only be defined as whatever the artist says it is (I.E. Picasso and the esteemed R. Mutt), literature must be defined in the broadest terms possible.
Art - In the broadest terms possible.
In its simplest form, this definition has two elements: written and storytelling.
I will start with storytelling because it is a meaningful word to me. Storytelling is an incredibly important part of human life and society. Children are taught lessons through stories and as a society we crave good stories in one form or another. For some that craving is satiated through film and television, for others through theater, and for many it is through comic books and novels.
In my mind, literature is by default fictional, or at least told with a fictional flair. The sometimes dry tone of most nonfiction work, even when dealing with historical subjects, excludes it from the distinction of literature because having a story at the heart of a work does not mean that story is being told.
That is by no means a bad thing. Its simply a different style of writing. Literature is, to me, synonymous with storytelling.
However, as mentioned earlier, storytelling comes in many forms, and not all of these mediums inherently belong to the class of literature.
Literature is by nature written. A prime example: Shakespeare. The many plays of Shakespeare take a form that are meant to be performed on stage. Yet, we study their text as literature. In much the same way, any number of novels may be considered literature where their stage or screen adaptations would not.
While the oral, and later visual, traditions have a place in the larger art of storytelling, literature is the product of taking a story and immortalizing it in print. It is a medium that brings nearly as much from the reader as it does from a writer to create a story, so that no two readings of the same text are exactly the same story. It asks the reader to bring their own flavor of imagination to the prompts of the text.
I choose to adopt a broad definition of this word because I have great respect for those authors of speculative fiction (I.E. Fantasy, Science Fiction, etc.) whose work may not count as literature in the eyes of professors and critics. Likewise, I consider many comic books and graphic novels to be of more depth than some "classically literary" works. I also believe that the canon is dangerous, as it judges what is truly a literary masterpiece by factors inapplicable to most of humanity, rather than the one factor that applies to everyone: how well the story is told.
And, of course, because how well something is told is completely subjective, it stands to reason that if somebody somewhere can be swept away by a story, then its a story.
So, I submit, perhaps to the chagrin of some, that if someone were to write the words "Johnny walked the dog. The dog ran away. Johnny cried." in ketchup on a napkin, it would count as literature.
