Aristotle proposes to discuss poetry, which he defines as a means of mimesis, or imitation, by means of language, rhythm, and harmony. As creatures who thrive on imitation, we are naturally drawn to poetry.

In particular, Aristotle focuses his discussion on tragedy, which uses dramatic, rather than narrative, form, and deals with agents who are better than us ourselves. Tragedy serves to arouse the emotions of pity and fear and to effect a katharsis (catharsis) of these emotions. Aristotle divides tragedy into six different parts, ranking them in order from most important to least important as follows: (1) mythos, or plot, (2) character, (3) thought, (4) diction, (5) melody, and (6) spectacle.

The first essential to creating a good tragedy is that it should maintain unity of plot. This means that the plot must move from beginning to end according to a tightly organized sequence of necessary or probable events. The beginning should not necessarily follow from any earlier events, and the end should tie up all loose ends and not produce any necessary consequences. The plot can also be enhanced by an intelligent use of peripeteia, or reversal, and anagnorisis, or recognition. These elements work best when they are made an integral part of the plot.

A plot should consist of a hero going from happiness to misery. The hero should be portrayed consistently and in a good light, though the poet should also remain true to what we know of the character. The misery should be the result of some hamartia, or error, on the part of the hero. A tragic plot must always involve some sort of tragic deed, which can be done or left undone, and this deed can be approached either with full knowledge or in ignorance.

Aristotle discusses thought and diction and then moves on to address epic poetry. Epic poetry is similar to tragedy in many ways, though it is generally longer, more fantastic, and deals with a greater scope of action. After addressing some problems of criticism, Aristotle argues that tragedy is superior to epic poetry.