And those decisions can vary a good deal from age to age and society to society

From Terry Eagleton, a British Marxist literary critic. I have not been able to track down the original article but have found it referenced here.

One of the permanent embarrassments of studying literature is that nobody has ever been able to come up with an adequate definition of what exactly it is. The dividing lines between 'literary' works and other forms of writing are notoriously blurred and unstable. Cardinal Newman is (perhaps) literature, but Charles Darwin is not; some execrable poetry in a 'high' mode belongs to the canon, but some superb contemporary science fiction in a more popular mode does not. East Enders is not literature, but quite a few turgid minor seventeenth-century dramas are. The poet, John Cooper Clarke, who can pack a fair-sized hall any night of the week, is not really literature, whereas a more respectable poet who would be lucky to pack a broom cupboard will be graced with the title. There is, in fact, no such thing as literature: literature is just the kind of writing which the cultural and academic establishments decide is literary. And those decisions can vary a good deal from age to age and society to society.