There is general agreement, which I share, that among the earliest of Western philosophers were three of the very greatest: Socrates, Plato and Aristotle. Each of these is on record as saying something – and it is almost the same thing – about the nature of philosophy itself that goes to the heart of the matter. Aristotle said: ‘It is owing to their wonder that men now begin, and first began, to philosophise’ (Metaphysics, i.982). And Plato wrote, putting his words into the mouth of Socrates: ‘This sense of wonder is the mark of the philosopher. Philosophy indeed has no other origin’ (Theaetetus, section 155).