This article examines Theophrastus’ deﬁnition of tragedy, as preserved by the Latin grammarian Diomedes, focusing on two questions that still need discussion. First, what is the meaning of the variously interpreted peristasis? An analysis of Diomedes’ text and a survey of the use of the word in Peripatetic works, both neglected by scholars up to now, suggest that it means “reversal”. Second, is the deﬁnition anti-Aristotelian? Not only katharsis, as is frequently emphasized, but, indeed, all the elements in Aristotle’s deﬁnition are absent from Theophrastus’. Nonetheless, references to characters and plot, on which Theophrastus’deﬁnition centres, can be found in Aristotle’s discussion of tragedy.