The ‘Digression’ in Plato’s Theaetetus: A New Interpretation

In this paper I argue that the “digression” (Tht. 172D-177C) plays a central role in Plato’s overall critique of Protagoras’s measure doctrine. Properly understood, the digression itself constitutes an argument against accepting a particular interpretation of the measure doctrine. This argument is based upon the unacceptable moral and political consequences that result from an institutional validation of extreme conventionalism. Commentators, such as Robin Waterfield and Gilbert Ryle, who dismiss this passage as pointless, and translators, such as Gwynneth Matthews, who omit the passage entirely, fail to draw the important connections among the measure doctrine, the Athenian legal system and its institutions, and the use of rhetoric. Drawing these connections enables one to discover the digression’s true meaning. Although the digression itself is highly rhetorical, Plato employs a type of rhetoric different from that licensed by the law courts. I argue that the three arguments from Tht. 170A-179D1 (the peritrope, the argument of the digression, and the argument based on expertise) form a powerful dialectical series against the Protagorean position. In this way, Plato’s use of rhetoric aims at improving the souls of those who read the digression, not at merely flattering them. This aim explains the very presence of the digression in the dialogue