And many arguments are used to show, that motion is the source of life, and rest of death: fire and warmth are produced by friction, and living creatures owe their origin to a similar cause; the bodily frame is preserved by exercise and destroyed by indolence; and if the sun ceased to move, "chaos would come again." Now apply this doctrine of "All is motion" to the senses, and first of all to the sense of sight. The colour of white, or any other colour, is neither in the eyes nor out of them, but ever in motion between the object and the eye, and varying in the case of every percipient. All is relative, and, as the followers of Protagoras remark, endless contradictions arise when we deny this; e.g. here are six dice; they are more than four and less than twelve; "more and also less," would you not say?' 'Yes.' 'But Protagoras will retort: "Can anything be more or less without addition or subtraction?"' 'I should say "No" if I were not afraid of contradicting my former answer.' 'And if you say "Yes," the tongue will escape conviction but not the mind, as Euripides would say?' 'True.' 'The thoroughbred Sophists, who know all that can be known, would have a sparring match over this, but you and I, who have no professional pride, want only to discover whether our ideas are clear and consistent. And we cannot be wrong in saying, first, that nothing can be greater or less while remaining equal; secondly, that there can be no becoming greater or less without addition or subtraction; thirdly, that what is and was not, cannot be without having become. But then how is this reconcilable with the case of the dice, and with similar examples?--that is the question.' 'I am often perplexed and amazed, Socrates, by these difficulties.' 'That is because you are a philosopher, for philosophy begins in wonder, and Iris is the child of Thaumas. Do you know the original principle on which the doctrine of Protagoras is based?' 'No.' 'Then I will tell you; but we must not let the uninitiated hear, and by the uninitiated I mean the obstinate people who believe in nothing which they cannot hold in their hands. The brethren whose mysteries I am about to unfold to you are far more ingenious. They maintain that all is motion; and that motion has two forms, action and passion, out of which endless phenomena are created, also in two forms--sense and the object of sense--which come to the birth together. There are two kinds of motions, a slow and a fast; the motions of the agent and the patient are slower, because they move and create in and about themselves, but the things which are born of them have a swifter motion, and pass rapidly from place to place. The eye and the appropriate object come together, and give birth to whiteness and the sensation of whiteness; the eye is filled with seeing, and becomes not sight but a seeing eye, and the object is filled with whiteness, and becomes not whiteness but white; and no other compound of