As the great period of Athenian drama drew to an end at the beginning of the 4th century BC, Athenian philosophers began to analyze its content and formulate its structure. In the thought of Plato (c. 427-347 BC), the history of the criticism of tragedy began with speculation on the role of censorship. To Plato (in the dialogue on the Laws) the state was the noblest work of art, a representation (mimesis) of the fairest and best life. He feared the tragedians' command of the expressive resources of language, which might be used to the detriment of worthwhile institutions. He feared, too, the emotive effect of poetry, the Dionysian element that is at the very basis of tragedy. Therefore, he recommended that the tragedians submit their works to the rulers, for approval, without which they could not be performed. It is clear that tragedy, by nature exploratory, critical, independent, could not live under such a regimen.

Plato is answered, in effect and perhaps intentionally, by Aristotle's Poetics. Aristotle (384-322 BC) defends the purgative power of tragedy and, in direct contradiction to Plato, makes moral ambiguity the essence of tragedy. The tragic hero must be neither a villain nor a virtuous man but a "character between these two extremes, . . . a man who is not eminently good and just, yet whose misfortune is brought about not by vice or depravity, but by some error or frailty [hamartia]." The effect on the audience will be similarly ambiguous. A perfect tragedy, he says, should imitate actions that excite "pity and fear." He uses Sophocles' Oedipus the King as a paradigm. Near the beginning of the play, Oedipus asks how his stricken city (the counterpart of Plato's state) may cleanse itself, and the world he uses for the purifying action is a form of the word catharsis. The concept of catharsis provides Aristotle with his reconciliation with Plato, a means by which to satisfy the claims of both ethics and art. "Tragedy," says Aristotle, "is an imitation [mimesis] of an action that is serious, complete and of a certain magnitude . . . through pity and fear effecting the proper purgation [catharsis] of these emotions." Ambiguous means may be employed, Aristotle maintains in contrast to Plato, to a virtuous and purifying end.

To establish the basis for a reconciliation between ethical and artistic demands, Aristotle insists that the principal element in the structure of tragedy is not character but plot. Since the erring protagonist is always in at least partial opposition to the state, the importance of tragedy lies not in him but in the enlightening event. "Most important of all," Aristotle said, "is the structure of the incidents. For tragedy is an imitation not of men but of an action and of life, and life consists in action, and its end is a mode of action, not a quality . . . ." Aristotle considered the plot to be the soul of a tragedy, with character in second place. The goal of tragedy is not suffering but the knowledge that issues from it, as the denouement issues from a plot. The most powerful elements of emotional interest in tragedy, according to Aristotle, are reversal of intention or situation (peripeteia) and recognition scenes (anagnorisis), and each is most effective when it is coincident with the other. In Oedipus, for example, the messenger who brings Oedipus news of his real parentage, intending to allay his fears, brings about a sudden reversal of his fortune, from happiness to misery, by compelling him to recognize that his wife is also his mother.