Aristotle's Poetics seeks to address the different kinds of poetry, the structure of a good poem, and the division of a poem into its component parts. He defines poetry as a ‘medium of imitation’ that seeks to represent or duplicate life through character, emotion, or action. Aristotle defines poetry very broadly, including epic poetry, tragedy, comedy, dithyrambic poetry, and even some kinds of music.
According to Aristotle, tragedy came from the efforts of poets to present men as 'nobler,' or 'better' than they are in real life. Comedy, on the other hand, shows a 'lower type' of person, and reveals humans to be worse than they are in average. Epic poetry, on the other hand, imitates 'noble' men like tragedy, but only has one type of meter - unlike tragedy, which can have several - and is narrative in form.
Aristotle lays out six elements of tragedy: plot, character, diction, thought, spectacle, and song. Plot is 'the soul' of tragedy, because action is paramount to the significance of a drama, and all other elements are subsidiary. A plot must have a beginning, middle, and end; it must also be universal in significance, have a determinate structure, and maintain a unity of theme and purpose.
Plot also must contain elements of astonishment, reversal (peripeteia), recognition, and suffering. Reversal is an ironic twist or change by which the main action of the story comes full-circle. Recognition, meanwhile, is the change from ignorance to knowledge, usually involving people coming to understand one another's true identities. Suffering is a destructive or painful action, which is often the result of a reversal or recognition.
All three elements coalesce to create "catharsis," which is the engenderment of fear and pity in the audience: pity for the tragic hero's plight, and fear that his fate might befall us.
When it comes to character, a poet should aim for four things. First, the hero must be 'good,' and thus manifest moral purpose in his speech. Second, the hero must have propriety, or 'manly valor.' Thirdly, the hero must be 'true to life.' And finally, the hero must be consistent.
Tragedy and Epic poetry fall into the same categories: simple, complex (driven by reversal and recognition), ethical (moral) or pathetic (passion). There are a few differences between tragedy and epic, however.
First, an epic poem does not use song or spectacle to achieve its cathartic effect. Second, epics often cannot be presented at a single sitting, whereas tragedies are usually able to be seen in a single viewing. Finally, the 'heroic measure' of epic poetry is hexameter, where tragedy often uses other forms of meter to achieve the rhythms of different characters' speech.
Aristotle also lays out the elements of successful imitation. The poet must imitate either things as they are, things as they are thought to be, or things as they ought to be. The poet must also imitate in action and language (preferably metaphors or contemporary words).
Errors come when the poet imitates incorrectly - and thus destroys the essence of the poem - or when the poet accidentally makes an error (a factual error, for instance). Aristotle does not believe that factual errors sabotage the entire work; errors that limit or compromise the unity of a given work, however, are much more consequential.
Aristotle concludes by tackling the question of whether the epic or tragic form is 'higher.' Most critics of his time argued that tragedy was for an inferior audience that required the gesture of performers, while epic poetry was for a 'cultivated audience' which could filter a narrative form through their own imaginations.
In reply, Aristotle notes that epic recitation can be marred by overdone gesticulation in the same way as a tragedy; moreover, tragedy, like poetry, can produce its effect without action - its power is in the mere reading.
Aristotle argues that tragedy is, in fact, superior to epic, because it has all the epic elements as well as spectacle and music to provide an indulgent pleasure for the audience. Tragedy, then, despite the arguments of other critics, is the higher art for Aristotle.