What is Aristotle's definition of a tragedy?

Aristotelean defined tragedy as "the imitation of an action that is serious and also, as having magnitude, complete in itself." It incorporates "incidents arousing pity and fear, wherewith to accomplish the catharsis of such emotions."

The tragic hero will most effectively evoke both our pity and terror if he is neither thoroughly good nor thoroughly evil but a combination of both. It is also important to not that Aristotle believed that while comedy is dark, because it laughs at human folly, tragedy represents human greatness, as the moment of catharsis shows man fighting against a superior force, despite knowing that ultimately they are doomed.