The Socrates of whom we know most is, however, quite differently engaged. He has devoted his life to a mission to his fellow men, and especially to his fellow citizens. If we may so far trust Plato's _Apology_, the occasion of that was the answer received from the Delphic oracle by Chaerephon, whom we know from Aristophanes as one of the leading disciples of Socrates in the earlier part of his life. Chaerephon asked the god of Delphi whether there was any one wiser than Socrates, and this of course implies that Socrates had a reputation for 'wisdom' before his mission began. The oracle declared that there was no one wiser, and Plato makes Socrates say in the _Apology_ that this was the real beginning of that mission. He set out at first to prove that the oracle was wrong, and for that purpose he tried to discover some one wiser than himself, a search in which he was disappointed, since he could only find people who thought they were wise, and no one who really was so. He therefore concluded that what the oracle really meant was that Socrates was wiser than other people in one respect only. Neither he nor any one else was really 'wise', but Socrates was wiser than the rest because he knew he was not wise and they thought they were. It ought to be clear that this is mostly 'irony', and it is not to be supposed that Socrates attached undue importance to the oracle, which he speaks of quite lightly, but he could hardly have told the story at all unless it was generally known that his mission did in fact date roughly from that period of his life. Historically it would probably be truer to say that the outbreak of the Peloponnesian War, in which Socrates served with great distinction as a hoplite, marked the decisive turning-point. It was in the camp at Potidaea that he once stood in a trance for twenty-four hours (431 B. C.), and that seems to point to some great psychological change, which may very well have been occasioned or accelerated by his experiences in the war. At any rate we now find him entirely devoted to the conversion of his fellow citizens, and we must try to understand what the message he had for them was.