Poetics (8.2-9.2)

But Homer, supreme also in all other respects, was apparently well aware of this truth either by instinct or from knowledge of his art. For in writing an Odyssey he did not put in all that ever happened to Odysseus, his being wounded on Parnassus, for instance, or his feigned madness when the host was gathered(these being events neither of which necessarily or probably led to the other), but he constructed his Odyssey round a single action in our sense of the phrase. And the Iliad the same.

As then in the other arts of representation a single representation means a representation of a single object, so too the plot being a representation of a piece of action must represent a single piece of action and the whole of it; and the component incidents must be so arranged that if one of them be transposed or removed, the unity of the whole is dislocated and destroyed. For if the presence or absence of a thing makes no visible difference, then it is not an integral part of the whole.

What we have said already makes it further clear that a poet’s object is not to tell what actually happened but what could and would happen either probably or inevitably.

The difference between a historian and a poet is not that one writes in prose and the other in verse—