For a thing whose presence or absence makes no visible difference, is not an organic part of the whole. 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 metre no less than without it. The true difference is that one relates what has happened, the other what may happen.
The quote: Poetry, therefore, is a more philosophical and a higher thing than history: for poetry tends to express the universal, history the particular.
By the universal, I mean how a person of a certain type will on occasion speak or act, according to the law of probability or necessity; and it is this universality at which poetry aims in the names she attaches to the personages. The particular is--for example--what Alcibiades did or suffered. In Comedy this is already apparent: for here the poet first constructs the plot on the lines of probability, and then inserts characteristic names;--unlike the lampooners who write about particular individuals.