This is a study of the significance and social function of tragic poetry as understood and explained by Aristotle in his treatise On the Art of Poetry. Like other works of the philosopher, the Poetics is at the same time descriptive and prescriptive, historical and theoretical: it deals with an art created and practiced almost exclusively in Athens in the fifth and earlier fourth centuries, although it was adopted by other Greeks in the second part of the fourth century, and later spread, alongside the Greek language, all over the Hellenistic world to become the mark of Hellenic culture in the centuries following the death of Aristotle and Alexander the Great. In the Poetics, Aristotle does not discuss the performance of drama as such. However, he considers music as a means of imitation -specifically, imitation of ethical qualities- which enhanced the signification of language in performance. He also puts forward a theory of reception of tragic poetry with regard to what he calls its "proper pleasure", which results from specific types of plot, representing terrible and pitiful events, and brings about in the end a "catharsis of such emotions". This elliptic statement is discussed in a central chapter with reference to the main theories of its interpretation: medical, ethical, and cognitive. A comprehensive new reading is proposed which combines all references to catharsis in Aristotelian texts with his teaching about the function of the emotions. For Aristotle, emotions are directly relevant to moral excellence, and also contribute to cognition and decision-making. His views about the emotions are seen to be confirmed by contemporary neural science.