Catharsis refers specifically to a purging of emotion for the audience, a purging that occurs when the truth finally comes out and the characters now understand everything that the audience does. In Oedipus Rex, for example, the audience experiences the tension developed by the play's dramatic irony: there are a great many clues that Oedipus is the killer of the prior king, Laius, and has, in fact, wed his mother and sired children by her. We understand that he is cursed and that he has promised to exile himself. And despite the fact that the audience knows Oedipus's true identity, it takes him a very long time to figure it out, and during all that time the audience's tension grows and grows. The audience can finally experience catharsis, the purging of all that tension and frustration, when Oedipus himself discovers who he is.  

It is difficult for us to sympathize with Oedipus while we witness his stubborn and self-righteous anger; we focus on his flaws—his rashness, his quickness to anger, his terrible pride. However, when we experience catharsis, we are now able to see Oedipus as more of a tragic figure. In short, we can sympathize with him now rather than merely criticize.  

Catharsis refers to a purging of emotions, purification and sometimes a renewal resulting from pity, sorrow, sympathy or even laughter. Catharsis applies to the experience of a character or the experience of the audience.

The term catharsis comes from Aristotle’s Poetics. He said that a catharsis was a purgation of pent up emotion. Plato believed poetry was emotional and irrational. But Aristotle saw poetry as an outlet for emotion; thus, a purgation.

This is usually when a character undergoes a mental or physical change, often because of suffering, and must experience an emotional overflow. The audience may identify and empathize with the character because suffering is universal. The experience of catharsis is meant to use this overflow of emotion as an outlet in order to return to a state of balance and harmony. For example, in It’s a Wonderful Life, George Bailey loses his temper, contemplates suicide and questions the purpose of his own existence. It is through this emotional and philosophical introspection and purging that he is able to put things into perspective and return to a harmonious life.

The most cited example is the tragedy of Oedipus Rex. Oedipus is a tragic figure. Some theorists have supposed that audiences get a cathartic relief when watching tragedies because they appreciate not being in the protagonist’s position. Oedipus blinding himself is the height of his cathartic experience: a total overflow of emotion. Aristotle said catharsis was the aesthetic function of a tragedy. That function is to bring the audience to an emotional height and then resolve the story, bringing them back down again.