This article aims at reconstructing the logic and assessing the force of Socrates' argument against Protagoras' 'Measure Doctrine' at Theaetetus 171a–c. I examine and criticise some influential interpretations of the passage, according to which, e.g., Socrates is guilty of ignoratio elenchi by dropping the essential Protagorean qualifiers or successfully proves that md is self-refuting provided the missing qualifiers are restored by the attentive reader. Having clarified the meaning of MD, I analyse in detail the broader section 170a–171d and argue, against (...) an extensive scholarly consensus, that it contains two slightly different formulations of the same argument, and not two distinct arguments, that Socrates does not highlight his own strategy at 171a–c as especially clever, and that his argument successfully shows that md turns out to be untenable for Protagoras himself when submitted to scrutiny in dialectical contexts, without aiming at proving its absolute falsehood. Finally, I clarify the philosophical import of the final image of Protagoras' momentary return from the underworld. (shrink)

Section 1 contrasts the approaches to Plato of F.M.Cornford and Gilbert Ryle, two of the early twentieth century’s leading Plato interpreters. Then I trace and evaluate attempts to discern in Plato’s Theaetetus a recognition of the role of the proposition. Section 2 focuses on the hunting of the proposition in Socrates’ Dream in the Theaetetus. Ryle, inspired by Logical Atomism, argued that Plato there anticipated an insight about the difference between names and propositions that Russell credited to Wittgenstein. I rehearse (...) difficulties for understanding the logos of the Dream as a proposition, preferring a reading of logos there as something like definition: a reading Wittgenstein also adumbrated. Section 3 examines attempts by writers such as Burnyeat and Kahn to find Plato allocating a starring role to the proposition in the argument at Theaetetus 185–6: perception, since it cannot grasp being, cannot grasp truth and hence cannot be knowledge. On their reading a grasp of being is understood as a grasp of something propositional. Problems for the propositional reading include Socrates’ talk of grasping ‘the truth of something’ (alētheia tinos), and the way the dialogue develops after 186. (shrink)