This is the first systematic analysis of Aristotle's concept of lexis. Ana Kotarcic argues that it should be approached on three interconnected levels: the first dealing with language as a system, the second with actual language usage, into which sociolinguistic factors come into play, and the third with prescriptions for the kind of language to be used in poetic and rhetorical compositions. She introduces ideas and concepts from classics and modern linguistics into the analysis alongside the philosophical approaches which have prevailed until now. The results reveal that Aristotle's ideas on lexis are complex, well-developed and intimately connected to many other fundamental concepts in his works, such as arete, energeia, ethos, logos, mimesis, pathos, phantasia and techne. A major component of his thought is therefore illuminated comprehensively for the first time.