Dialectic is a vital element in all Greek philosophy, and some would extend that comment to all philosophy. The merit of the Greek philosophers is that this feature applies to them all without qualification. If that is true of Greek philosophy in general, it is especially true of Plato. For him dialectic was a style of philosophy, a method, and also a science.

Socrates wrote nothing philosophical (in the Phaedo he is described as writing poems) and was not given to lengthy expositions. Instead he conducted his enquiries by question and answer; although he typically only reached negative conclusions – that the person he was speaking with was ignorant of the topic, that his earlier position was wrong and refutable – there is still a sense that something positive is achieved by Socrates' dialectical probing. At the beginning of Chapter 2 we looked at some of the more obviously positive results that arose from this Socratic method. But Plato sensed that there was more to the power of this method than just these particular results. It held the key to the achievement of purely rational knowledge. He therefore tries to develop the conversational method into a science capable of yielding substantive bodies of knowledge. We shall follow these developments as they unfold over Plato's philosophical career. I look at Aristotle's critical comments on these proposals. Finally, I consider whether and how dialectic operates in Plato's philosophy in some other, less scientific and more philosophical manner.