Moral evaluation of characters in Hippolytus has always been an important part of the play’s criticism. Scholars’ opinions range from blaming all of them to excusing and even praising both Phaedra and Hippolytus; some critics see moral failure in Phaedra’s behaviour, while others give more attention to Hippolytus’ guilt. This article proposes a solution of the problem of moral evaluation in the tragedy through finding a connection between its moral themes and patterns of behaviour represented in the play and the topos of involuntary faults used in Athenian apologetic rhetoric. Through an analysis of this topos in forensic speeches, those in Thucydides’ History and in a number of philosophic texts using rhetorical topics (Gorgias, Plato, Aristotle), its major constitutive elements are identified. The postulated involuntariness of a wrongdoing gives grounds for exonerating it, and there existed a fixed list of extenuating circumstances that allowed to acknowledge a wrongdoing as involuntary, which included ignorance, emotions or external causes (misfortune or another person’s will). Euripides uses all the elements of this topos in his Hippolytus, making them into his key thematic motifs and actualizing their dramatic force, so that the idea of exoneration explicitly and dramatically expressed in the exodus becomes the logical consequence of the entire action of the tragedy.