Scholars have occasionally noted that the Antigone’s abundant images of polar opposition bear resemblance to the fragments of Heraclitus and his doctrine of the ‘unity of opposites’. The present essay develops this comparison and explores its implications for our interpretation of the play, presenting a test case for the value of the Presocratics in the study of Attic tragedy. It argues that Heraclitus’ surviving work provides a valuable resource for elucidating the play’s ‘cosmology’, a term here used in its anthropological sense to refer to presuppositions, rather than explicitly articulated theories, concerning the structure of the universe and humanity’s place within it. This endeavour can affect our understanding of two points of intense interpretative disagreement: the rationality of the central protagonists and the role of polar oppositions in the play. A culturally sensitive evaluation of the characters’ rationality must take account of the rules of the cosmos they inhabit. The polar oppositions hint at a regular and systematic cosmology, but its finer details are ultimately kept obscure to the audience, and only Teiresias displays a substantial understanding of this underlying framework. Heraclitus thus enriches our understanding of the epistemological predicament in which the characters find themselves.