Aristotle proposes to study poetry by analyzing its constitutive parts and then drawing general conclusions. The portion of the Poetics that survives discusses mainly tragedy and epic poetry. We know that Aristotle also wrote a treatise on comedy that has been lost. He defines poetry as the mimetic, or imitative, use of language, rhythm, and harmony, separately or in combination. Poetry is mimetic in that it creates a representation of objects and events in the world, unlike philosophy, for example, which presents ideas. Humans are naturally drawn to imitation, and so poetry has a strong pull on us. It can also be an excellent learning device, since we can coolly observe imitations of things like dead bodies and disgusting animals when the real thing would disturb us.
Aristotle identifies tragedy as the most refined version of poetry dealing with lofty matters and comedy as the most refined version of poetry dealing with base matters. He traces a brief and speculative history of tragedy as it evolved from dithyrambic hymns in praise of the god Dionysus. Dithyrambs were sung by a large choir, sometimes featuring a narrator. Aeschylus invented tragedy by bringing a second actor into dialogue with the narrator. Sophocles innovated further by introducing a third actor, and gradually tragedy shifted to its contemporary dramatic form.
Aristotle defines tragedy according to seven characteristics: (1) it is mimetic, (2) it is serious, (3) it tells a full story of an appropriate length, (4) it contains rhythm and harmony, (5) rhythm and harmony occur in different combinations in different parts of the tragedy, (6) it is performed rather than narrated, and (7) it arouses feelings of pity and fear and then purges these feelings through catharsis. A tragedy consists of six component parts, which are listed here in order from most important to least important: plot, character, thought, diction, melody, and spectacle.
A well-formed plot must have a beginning, which is not a necessary consequence of any previous action; a middle, which follows logically from the beginning; and an end, which follows logically from the middle and from which no further action necessarily follows. The plot should be unified, meaning that every element of the plot should tie in to the rest of the plot, leaving no loose ends. This kind of unity allows tragedy to express universal themes powerfully, which makes it superior to history, which can only talk about particular events. Episodic plots are bad because there is no necessity to the sequence of events. The best kind of plot contains surprises, but surprises that, in retrospect, fit logically into the sequence of events. The best kinds of surprises are brought about by peripeteia, or reversal of fortune, and anagnorisis, or discovery. A good plot progresses like a knot that is tied up with increasingly greater complexity until the moment of peripeteia, at which point the knot is gradually untied until it reaches a completely unknotted conclusion.
For a tragedy to arouse pity and fear, we must observe a hero who is relatively noble going from happiness to misery as a result of error on the part of the hero. Our pity and fear is aroused most when it is family members who harm one another rather than enemies or strangers. In the best kind of plot, one character narrowly avoids killing a family member unwittingly thanks to an anagnorisis that reveals the family connection. The hero must have good qualities appropriate to his or her station and should be portrayed realistically and consistently. Since both the character of the hero and the plot must have logical consistency, Aristotle concludes that the untying of the plot must follow as a necessary consequence of the plot and not from stage artifice, like a deus ex machina (a machine used in some plays, in which an actor playing one of the gods was lowered onto the stage at the end).
Aristotle discusses thought and diction and then moves on to address epic poetry. Whereas tragedy consists of actions presented in a dramatic form, epic poetry consists of verse presented in a narrative form. Tragedy and epic poetry have many common qualities, most notably the unity of plot and similar subject matter. However, epic poetry can be longer than tragedy, and because it is not performed, it can deal with more fantastic action with a much wider scope. By contrast, tragedy can be more focused and takes advantage of the devices of music and spectacle. Epic poetry and tragedy are also written in different meters. After defending poetry against charges that it deals with improbable or impossible events, Aristotle concludes by weighing tragedy against epic poetry and determining that tragedy is on the whole superior.