 This way of reading Plato’s dialogues does not presuppose that he never changes his mind about anything—that whatever any of his main interlocutors uphold in one dialogue will continue to be presupposed or affirmed elsewhere without alteration. It is, in fact, a difficult and delicate matter to determine, on the basis of our reading of the dialogues, whether Plato means to modify or reject in one dialogue what he has his main interlocutor affirm in some other. One of the most intriguing and controversial questions about his treatment of the forms, for example, is whether he concedes that his conception of those abstract entities is vulnerable to criticism; and, if so, whether he revises some of the assumptions he had been making about them, or develops a more elaborate picture of them that allows him to respond to that criticism (see Meinwald 2016). In Parmenides, the principal interlocutor (not Socrates—he is here portrayed as a promising, young philosopher in need of further training—but rather the pre-Socratic from Elea who gives the dialogue its name: Parmenides) subjects the forms to withering criticism, and then consents to conduct an inquiry into the nature of oneness that has no overt connection to his critique of the forms. Does the discussion of oneness (a baffling series of contradictions—or at any rate, propositions that seem, on the surface, to be contradictions) in some way help address the problems raised about forms? That is one way of reading the dialogue. And if we do read it in this way, does that show that Plato has changed his mind about some of the ideas about forms he inserted into earlier dialogues? Can we find dialogues in which we encounter a “new theory of forms”—that is, a way of thinking of forms that carefully steers clear of the assumptions about forms that led to Parmenides’ critique? It is not easy to say. But we cannot even raise this as an issue worth pondering unless we presuppose that behind the dialogues there stands a single mind that is using these writings as a way of hitting upon the truth, and of bringing that truth to the attention of others. If we find Timaeus (the principal interlocutor of the dialogue named after him) and the Eleatic visitor of the Sophist and Statesman talking about forms in a way that is entirely consistent with the way Socrates talks about forms in Phaedo and Republic, then there is only one reasonable explanation for that consistency: Plato believes that their way of talking about forms is correct, or is at least strongly supported by powerful considerations. If, on the other hand, we find that Timaeus or the Eleatic visitor talks about forms in a way that does not harmonize with the way Socrates conceives of those abstract objects, in the dialogues that assign him a central role as director of the conversation, then the most plausible explanation for these discrepancies is that Plato has changed his mind about the nature of these entities. It would be implausible to suppose that Plato himself had no convictions about forms, and merely wants to give his readers mental exercise by composing dialogues in which different leading characters talk about these objects in discordant ways.