In his Poetics, Aristotle defines tragedy as “an imitation (mimēsis) of an action that is serious, complete, and of a certain magnitude.” He asserts that any tragedy can be divided into six constituent parts: plot, character, thought, diction, song and spectacle, and—the most important of all—the first principle, the plot, described as the “soul of a tragedy.” Furthermore, he states that the key components here are the unity and the wholeness of the plot. Everything that happens, every element and every event, must work together in order to form a whole.

So the plot, being an imitation of an action, must imitate one action and that a whole, the structural union of the parts being such that, if any one of them is displaced or removed, the whole will be disjointed and disturbed.

The plot must have a beginning, a middle, and an end. He argues that a well-structured plot must retain “a length easily embraced by the memory.” If done right, the reader or the watcher will feel a “tragic pleasure of pity and fear” when processing the plot, and, essentially, this is what distinguishes tragedy from other literary genres. The audience usually feels pity for the tragic hero, who, due to known or unknown circumstances, has been through something traumatic and life-changing. The hero must be neither good nor evil, but rather human and real so that the audience can identify with their character, and when they finally face their downfall due to some mistake or lapse in judgement, the audience can empathize. He writes:

Tragedy is a form of drama exciting the emotions of pity and fear. Its action should be single and complete, presenting a reversal of fortune, involving persons renowned and of superior attainments, and it should be written in poetry embellished with every kind of artistic expression.

There are several main feature to an ideal plot in tragedy according to  Aristotle's Poetics. First, the action of the plot may be either single or double. It must be of a certain magnitude and seriousness. The tragic plot must revolve around people who have a certain measure of greatness, but may have some inherent character flaw leading to their downfall. The tragedy should display unities of time, place and action. A tragedy must be complete in having a beginning, middle, and an end. Most plots contain a moment of reversal, when an act of a character results in an inevitable but unintended consequence. Aristotle defines tragedy as follows:

...an imitation of an action that is serious, complete, and of a certain magnitude; in language embellished with each kind of artistic ornament, ... in the form of action, not of narrative; through pity and fear effecting the proper purgation of these emotions.