Unity of plot does not, as some persons think, consist in the Unity of the hero. For infinitely various are the incidents in one man's life which cannot be reduced to unity; and so, too, there are many actions of one man out of which we cannot make one action. Hence, the error, as it appears, of all poets who have composed a Heracleid, a Theseid, or other poems of the kind. They imagine that as Heracles was one man, the story of Heracles must also be a unity. But Homer, as in all else he is of surpassing merit, here too--whether from art or natural genius--seems to have happily discerned the truth. In composing the Odyssey he did not include all the adventures of Odysseus--such as his wound on Parnassus, or his feigned madness at the mustering of the host--incidents between which there was no necessary or probable connection: but he made the Odyssey, and likewise the Iliad, to centre round an action that in our sense of the word is one. As therefore, in the other imitative arts, the imitation is one when the object imitated is one, so the plot, being an imitation of an action, must imitate one action and that a whole, the structural union of the parts being such that, if any one of them is displaced or removed, the whole will be disjointed and disturbed. For a thing whose presence or absence makes no visible difference, is not an organic part of the whole. IX 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. 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. But tragedians still keep to real names, the reason being that what is possible is credible: what has not happened we do not at once feel sure to be possible: but what has happened is manifestly possible: otherwise it would not have happened. Still there are even some tragedies in which there are only one or two well known names, the rest being fictitious. In others, none are well known, as in Agathon's Antheus, where incidents and names alike are fictitious, and