linguistic:paraphrasing, information:extraction
Aristotle

Aristotle wrote in his work Poetics thattragedy is characterised by seriousness and involves a great person who experiences a reversal of fortune (Peripeteia). Aristotle's definition can include a change of fortune from bad to good as in the Eumenides, but he says that the change from good to bad as in Oedipus Rex is preferable because this induces pity and fear within the spectators. Tragedy results in a catharsis (emotional cleansing) or healing for the audience through their experience of these emotions in response to the suffering of the characters in the drama.

According to Aristotle, "the structure of the best tragedy should not be simple but complex and one that represents incidents arousing fear and pity —for that is peculiar to this form of art." This reversal of fortune must be caused by the tragic hero's hamartia, which is often translated as either a character flaw, or as a mistake (since the original Greek etymology traces back to hamartanein, a sporting term that refers to an archer or spear -thrower missing his target). According to Aristotle, "The misfortune is brought about not by vice or depravity, but by some error or frailty." The reversal is the inevitable but unforeseen result of some action taken by the hero. It is also a misconception that this reversal can be brought about by a higher power (e.g. the law, the gods, fate, or society), but if a character's downfall is brought about by an external cause, Aristotle describes this as a misadventure and not a tragedy.

In addition, the tragic hero may achieve some revelation or recognition (anagnorisis —"knowing again" or "knowing back" or "knowing throughout") about human fate, destiny, and the will of the gods. Aristotle terms this sort of recognition "a change from ignorance to awareness of a bond of love or hate."

In Poetics, Aristotle gave the following definition in ancient Greek of the word "tragedy" (τραγῳδία):

Tragedy is an imitation of an action that is admirable, complete (composed of an introduction, a middle part and an ending), and possesses magnitude; in language made pleasurable, each of its species separated in different parts; performed by actors, not through narration; effecting through pity and fear the purification of such emotions.

Common usage of tragedy refers to any story with a sad ending, whereas to be an Aristotelian tragedy the story must fit the set of requirements as laid out by Poetics. By this definition social drama cannot be tragic because the hero in it is a victim of circumstance and incidents that depend upon the society in which he lives and not upon the inner compulsions—psychological or religious—which determine his progress towards self-knowledge and death. Exactly what constitutes a "tragedy", however, is a frequently debated matter.

According to Aristotle, there are four species of tragedy: