Aristotle: History and Poetry

It is, moreover, evident from what has been said, that it is not the
function of the poet to relate what has happened, but what may happen-
what is possible according to the law of probability or necessity. The
poet and the historian differ not by writing in verse or in prose. The
work of Herodotus might be put into verse, and it would still be a
species of history, with meter no less than without it. The true
difference is that one relates what has happened, the other what may
happen. Poetry, therefore, is a more philosophical and a higher
thing than history: for poetry tends to express the universal, history
the particular.

Aristotle: Poetics