Glossary of Literary Theory by Greig E. Henderson and Christopher Brown

Catharsis:

An Aristotelian term for the purgative or purifying effect that the imitation of victimage in tragedy has upon an audience. According to Aristotle, a tragedy is a dramatic form "with incidents arousing pity and fear wherewith to accomplish the catharsis of such emotion." By allowing spectators to load their emotions onto a scapegoat, tragedy cleanses them of harmful tensions which would otherwise poison their mental health. It also purifies these emotions and forces the audience to undergo a process of ethical clarification. Catharsis, therefore, is morally as well as psychologically therapeutic.