With this, of course, is connected the doctrine of {217} transmigration, which Plato took, no doubt, from the Pythagoreans. Most of the details of Plato's doctrine of transmigration are mere myth. Plato does not mean them seriously, as is shown by the fact that he gives quite different and inconsistent accounts of these details in different dialogues. What, in all probability, he did believe, however, may be summarized as follows. The soul is pre-existent as well as immortal. Its natural home is the world of Ideas, where at first it existed, without a body, in the pure and blissful contemplation of Ideas. But because it has affinities with the world of sense, it sinks down into a body. After death, if a man has lived a good life, and especially if he has cultivated the knowledge of Ideas, philosophy, the soul returns to its blissful abode in the world of Ideas, till, after a long period it again returns to earth in a body. Those who do evil suffer after death severe penalties, and are then reincarnated in the body of some being lower than themselves. A man may become a woman. Men may even, if their lives have been utterly sensual, pass into the bodies of animals. 5. Ethics _(a) The Ethics of the Individual_ Just as Plato's theory of knowledge begins with a negative portion, designed to refute false theories of what truth is, so does his theory of morals begin with a negative portion, intended to refute false theories of what virtue is. These two negative departments of Plato's philosophy correspond in every way. As he was then engaged in showing that knowledge is not perception, as Protagoras thought, so he now urges that {218} virtue is not the same as pleasure. And as knowledge is not mere right opinion, neither is virtue mere right action. The propositions that knowledge is perception, and that virtue is pleasure, are indeed only the same principle applied to different spheres of thought. For the Sophists whatever appeared true to the individual was true for that individual. This is the same as saying that knowledge is perception. For the Sophists, again, whatever appeared right to the individual was right for that individual. This is the same as saying that it is right for each man to do whatever he pleases. Virtue is defined as the pleasure of the individual. This consequence of the Sophistic principles was drawn both by many of the Sophists themselves, and later by the Cyrenaics. As these two propositions are thus in fact only one principle, what Plato has said in refutation of the former provides also his refutation of the latter. The theory that virtue is pleasure has the same destructive influence upon morals as the theory that knowledge is perception had upon truth. We may thus shortly summarize Plato's arguments.