The Incredible Vanishing Measure Doctrine (Theaetetus 170a3–171d8)

Abstract This paper offers a reading of Theaetetus 170a3–171d8 with two main advantages: it accounts for Socrates’ concern with the sheer number of people who reject the Measure Doctrine, and it shows how every part of the passage supports Socrates’ argument. It also proposes a new account of that argument’s structure: it is a constructive dilemma with a regress on the second arm. The argument properly ascribes to Protagoras a principle relating appearance and reality for any complex subject to appearance and reality for that subject’s parts.