Defining Literature Part 3

What is the difference between epics, novels, novellas, stories, narratives, texts, discourses, poetry, lyrics, speeches, manuscripts, reports, pamphlets, brochures, textbooks, catalogs, letters, etc? More importantly, what is the common thread that holds them all together? I always assumed that they all fell under the general category of “literature”, because they all appear to be written literary works, and what else does something need to be to be properly called “literature”? I truly do believe that a necessary condition for literature is to be written, but I now question whether or not being written is sufficient for the definition. After all, I don’t want to be radically inclusive. So what kind of criteria can we make for "literature"? What are the distinguishing factors between other various written works? What are the sufficient conditions for putting a work in the category of  "literature"? The authors' intention is one thing that should be considered. If an author did not mean for a work to be "literature", then perhaps it should not be called so. On the other hand, if an author did mean for a work to be "literature", does that automatically make it so? I think not. At least, it is not sufficient enough. But maybe intention could be a necessary condition for "literature". When one looks at fictional works vs. non-fictional ones, it can be very difficult to find the common thread that allow them to both be called "literature". I would think that this would make the criteria for "literature" incredibly small. I think we can at least say "being written" is one of the criteria, and "authors' intention" might be another, but after that I must say that I am at a loss. The factors vary so much from one written piece to another that I simply cannot come up with an adequate definition of "literature". But, I would be very anxious to know if anyone else can...