 These features of the dialogues show Plato’s awareness that he cannot entirely start from scratch in every work that he writes. He will introduce new ideas and raise fresh difficulties, but he will also expect his readers to have already familiarized themselves with the conversations held by the interlocutors of other dialogues—even when there is some alteration among those interlocutors. (Meno does not re-appear in Phaedo; Timaeus was not among the interlocutors of Republic.) Why does Plato have his dominant characters (Socrates, the Eleatic visitor) reaffirm some of the same points from one dialogue to another, and build on ideas that were made in earlier works? If the dialogues were merely meant as provocations to thought—mere exercises for the mind—there would be no need for Plato to identify his leading characters with a consistent and ever-developing doctrine. For example, Socrates continues to maintain, over a large number of dialogues, that there are such things as forms—and there is no better explanation for this continuity than to suppose that Plato is recommending that doctrine to his readers. Furthermore, when Socrates is replaced as the principal investigator by the visitor from Elea (in Sophist and Statesman), the existence of forms continues to be taken for granted, and the visitor criticizes any conception of reality that excludes such incorporeal objects as souls and forms. The Eleatic visitor, in other words, upholds a metaphysics that is, in many respects, like the one that Socrates is made to defend. Again, the best explanation for this continuity is that Plato is using both characters—Socrates and the Eleatic visitor—as devices for the presentation and defense of a doctrine that he embraces and wants his readers to embrace as well.