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.