As imitative arts Aristotle mentions poetry, dancing, music, and painting. They differ, he says, in their medium, objects, and manner. Poetry, dancing, and music he classifies together because they use the similar media of rhythm, language, or harmony either singly or combined. Music, for instance, uses both rhythm and harmony, dancing uses rhythm alone, and poetry uses language alone. Aristotle by this does not, as might seem, exclude rhythm and harmony from poetry. Indeed, he states explicitly that most forms of poetry do use all of the media mentioned: rhythm, tune, and meter. He is only insisting that imitation in unmetrical language is still poetry; that meter is not the characteristic element of poetic.[[16]] It is important to recognize that in classifying poetry with music and dancing, Aristotle is insisting that the common element in these arts is movement. Movement is characteristic of poetry, as color and form are characteristic of painting and sculpture. Thus in discussing the plot of tragedy, which he holds to be the highest and most characteristic form of poetry, Aristotle urges the necessity of unity and magnitude, both of which he defines in terms not of space relations, but of movement. For instance, to possess unity a plot must have a beginning, a middle and an end.
A beginning is that which does not itself follow anything by causal necessity, but after which something naturally is or comes to be. An end, on the contrary, is that which itself naturally follows some other thing, either by necessity, or as a rule, but has nothing following it. A middle is that which follows something as some other thing follows it.[[17]]
Furthermore, the magnitude which this dramatic movement should possess is also discussed not in terms of bulk, but of length.
As, therefore, in the case of animate bodies and organisms, a certain magnitude is necessary, and a magnitude which may be easily embraced in one view; so in the plot, a certain length is necessary, and a length which can easily be embraced by the memory.[[18]]
It is noteworthy that to Aristotle the characteristic movement of poetic depends on the dramatic unity and progression of a dramatic action, a plot. In the Rhetoric he shows that the arrangement of the movement of a speech is governed by entirely different considerations. The unity of rhetoric is not dramatic, but logical. The order of the parts of a speech is determined not by a plot, but by the needs of presentation to an audience. For instance, a statement of the case is given first, and then the proof is marshalled.
The objects of poetic imitation, Aristotle says, are character, emotion, and deed, i.e., men in action,[[19]] inanimate nature and the life of dumb animals being subordinate to these. The manner of imitating, if poetic, Aristotle says is either narrative or dramatic. Under the narrative manner he includes lyric, where the speaker expresses himself in the first person, and epic, where the speaker tells his story in the third person. In the dramatic manner he says that the characters are made to live and move before us.[[20]]
Answering Plato's charge that poetic is not real, Aristotle erects the distinction between the real and the actual, claiming a reality for poetic which is not the actuality of science or of practical affairs. It is thus that he distinguishes the poet from the historian: although the historian also uses images, he is restricted to relating what has happened--that is, to fact; while the poet relates what should happen--what is possible according to the law of probability or necessity. Instead of rehearsing facts, the dramatist or the epic poet creates truth. We expect him to be "true to life," and that is what is implied in Aristotle's "imitation of nature."[[21]] This truth to life controls, according to Aristotle, both the characterization and the action. In the first place
Poetry tends to express the universal--how a person of a certain type will on occasion speak or act according to the law of probability or necessity.[[22]]
Aristotle goes so far as to say that probability, not actuality, controls the structure of a narrative or dramatic plot in that, "what follows should be the necessary or probable result of the preceding action,"[[23]] even to the extent that the poet should prefer probable impossibilities to improbable possibilities, for by a logical fallacy even an irrational premise in an action may seem probable provided that the conclusion is logical and made to seem real.[[24]] For instance, the irrational elements in the Odyssey "are presented to the imagination with such vividness and coherence that the impossible becomes plausible; the fiction looks like truth."[[25]] Such a result occurs only when the characters and action are made real. We believe that which we see, even though we know in our hearts that it is not so.
How important Aristotle feels it to be that the spectator or reader should see before him the characters and situations of an epic or drama is evinced by his suggestion to the poet on the process of composing. The author, he says, should visualize the situations he is presenting, working out the appropriate gestures, for he who feels emotion is best at transmitting it to an audience.[[26]] It is only when the poet thus completely realizes his characters and situations that the audience can be induced to feel sympathetically the pity and fear which produces the katharsis, so important a result of successful tragedy. If human beings did not possess that tendency to feel within themselves the emotions of the people on the stage, they would be unable to experience vicariously the fear animating the tragic hero. Thus tragedy, which is the type of all poetic, depends vitally, according to Aristotle, on imaginative realization.