The dialogue form in which Plato writes is more than a mere literary device; it is instead an expression of Plato’s understanding of the purpose and nature of philosophy. For Plato, philosophy is a process of constant questioning, and questioning necessarily takes the form of dialogue. Near the end of the Phaedrus, Socrates expresses his reservations about written texts, worrying that people will cease to think for themselves when they have someone else’s thoughts written out in front of them. Plato took it upon himself to write his thoughts down anyway, but he was careful not to write them in such a way that we could easily assimilate his thoughts rather than thinking for ourselves. Many of the dialogues reach no definite conclusions, and those that do generally approach those conclusions by casting doubts and examining possible counterarguments. Plato cannot be there in person to share his thoughts with us, but he wants to ensure that we think through them ourselves.
In keeping with this emphasis on dialogue form, Plato develops an increasingly complex conception of dialectic, or logical argument, as the engine that drives philosophical investigations. In the early dialogues, dialectic consists of Socrates cross-examining and refuting his interlocutors until he brings them to a state of perplexity, or aporia. Beginning with the Meno, Plato recognizes that dialectic can lead people not only to recognize their errors but also to positive discoveries, as Socrates does with the slave boy in Meno. Plato is sufficiently impressed with the possibilities of the dialectic that, in The Republic, he makes it the highest achievement of his rigorous education program. The Phaedrus introduces a more systematic version of the dialectic, seeing it as a matter of “division and generalization,” whereby we analyze concepts so as to understand the precise relations between them. This process of division and generalization becomes increasingly sophisticated throughout Plato’s works, and we witness advanced versions of it in the Parmenides and the Sophist.