Imitation or mimesis is almost a byword of literary criticism, and almost certainly Plato is the progenitor of the term, for it is he who introduces it in Greek philosophy while speaking of his theory of forms or ideas. Whether any theory of poetry as imitation was developed before Plato is uncertain. Gorgias notion of tragedy as a beneficent deception perhaps anticipated it in part. Democritus, too, held that the arts in general arose out of imitation of nature. Singing, for example, is nothing but the imitation of the birds. But the first significant writing where one can grasp mimesis as a critical term is in Platos The Republic (Book III, Book x). However, Book III is more concerned with political and pedagogical issues. It is in Book x that imitation occurs as a literary term. Plato does not directly say that all poetry is imitation, but through his theory of ideas, he points out that the average artist or poet can only try to imitate the original supernal, unparalleled entity that exists only as an idea.

The philosophical basis of the theory of ideas is that there is an ideal form, and that the visible things on the earth are only the imperfect copies of the original. Human beings cannot normally attain to knowledge of this ideal form and are therefore limited to the world of senses. Plato gives two analogies. The first is the analogy of the prisoners in a cave with a fire burning behind them. The prisoners themselves cannot see the fire though they can see the shadow cast by them against the wall. The fire is symbolic of that knowledge as the supreme reality, of that ideal form, which the human beings cannot normally conceive of.

Another analogy is that of the Divided Line. This line divides different stages or strata of knowledge: at the bottom is EIKASIA or sensory knowledge. Just above this is PISTIS or opinion, the knowledge that the vulgar literature possesses. Above that is the relatively higher kind of knowledge known as understanding or DIANOIA. This is the knowledge possessed by those men who are both learned and thoughtful. The supreme knowledge is NOESIS or intuitive understanding. Such knowledge appertains to the supreme reality which is the knowledge of the ideal form. Such knowledge is possessed only by the wise. Plato mentions these analogies because he wants to point out the fact that the authors of literature are prisoners of the cave who do not themselves know of the ideal form. They do not have NOESIS or the supreme knowledge. Therefore poetry deals only with the sensible reality which is different from the truth.

Plato gives the detailed analysis of the way in which poetry presents a distorted version of the ideal form. The real world is that of EIDOS, the thing in itself. From that is derived the world of appearances including things made by earthly technicians and craftsmen. But they too have deviated from the truth. It is from this world that the poets derive materials for the world of literature. Thus, the world of the poets is the farthest removed from the truth. Plato gives the example of a bed. He says that there is only one original bed created by god which is the original idea. It is from this that the carpenter makes the bed we sleep upon. And it is from imitation of the carpenter that the poet finds material for the bed which he represents in his poetry. Therefore Plato happily declares that the poet is at third removed from the throne of truth. He goes on to add that the same is true of all representative poets.

Plato also gives another example of the limited nature and scope of the poets knowledge of truth. He says that there are three skills- that of the user, of the manufacturer, and of the artist. While the user has the greatest practical knowledge, the manufacturer gains this knowledge because he has to produce the article to the satisfaction of the user. The artist has neither the knowledge of the user nor of the manufacturer. He can neither make the article nor use it and therefore does not understand it. Thus while the user and the manufacturer can serve the society, the poet cannot.

Plato has often spoken of the frenzy of the poet, a frenzy which leads the poets to have more than average knowledge. In ION and PHAEDRUS he has called the poet a light and wind and holy thing and he has also called the poet an inspired being who in his enthusiasm reaches to a state beyond the ordinary. Yet this is not necessarily praise because inspiration is akin to insanity.

Thus the conclusions to be drawn from Platos theory of ideas are chiefly two. The first is that all poetry is imitation. The second is that this imitation is not a perfect imitation but a distortion, and that, therefore, the poets art ought not to be encouraged but rather banished as being philosophy false. Although the second conclusion has often been subjected to severe criticism for its extra-aesthetic criticism of art, the first conclusion of poetry being an imitation stands as an abiding contribution to literary criticism.