In 476 lines of dactylic hexameter, one of the great Roman poets tells us, if not how he wrote his songs, at any rate how we should go about writing ours. The advice is not all his own; an ancient commentator notes that the poet drew some of it from a third-century BC Greek critic called Neoptolemus of Parium. But it is Horace’s version that has lasted. The Ars lays down literary laws observed by writers for centuries: modern editions divide Shakespeare’s plays into five acts, for instance, because that’s how many Horace said a play should have. It canonized critical ideas, like the concept of artistic unity, that we now take as self-evident.
Source : Horace’s How-To
