The philosophy of Plato has the curious property of being delivered almost entirely through the mouth of someone else. Nearly all his surviving works are ‘dialogues’: transcripts of real or imaginary conversations between groups of acquaintances, in which the chief protagonist is his teacher Socrates. In the dialogues, Socrates is the exponent of the doctrines that Plato wishes to recommend. In principle, it is possible to isolate Socrates’ actual opinions from those attributed to him by Plato, but the distinction is problematical, and we shall not try to deal with it. Of Socrates himself we know only what can be gleaned from Plato’s dialogues, from the writings of Xenophon, and from the fact that he is sent up in Aristophanes’ comedy Clouds. A stonemason by trade, he preferred to spend his time discussing philosophy with friends. He wrote nothing. His ‘dialectical’ method consists in the clarification of concepts by a process of question and answer called elenchos. He sees himself not as teaching anything new, but as encouraging people to understand what they know already. He is also a self-proclaimed ‘gadfly’ whose mission is to pester people into realising that what they think they know is not really knowledge at all.