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.