Descartes therefore made no discovery in pointing out this fact as an irreversible certainty. The part it plays in his system is only that of a starting-point. It makes consciousness the basis of all truth. There is none other possible. Interrogate consciousness, and its clear replies will be science. Here we have a new basis and a new philosophy introduced. It was indeed but another shape of the old formula, "Know thyself," so differently interpreted by Thales, Socrates, and the Alexandrians; but it gave that formula a precise signification, a thing it had before always wanted. Of little use could it be to tell man to know himself. How is he to know himself? By looking inward? We all do that. By examining the nature of his thoughts? That had been done without success. By examining the process of his thoughts? That, too, had been accomplished, and the logic of Aristotle was the result. The formula needed a precise interpretation; and that interpretation Descartes gave. Consciousness, said he, is the basis of all knowledge; it is the only ground of absolute certainty. Whatever it distinctly proclaims must be true. The process, then, is simple: examine your consciousness, and its clear replies. Hence the vital portion of his system lies in this axiom: All clear ideas are true: whatever is clearly and distinctly conceived is true. This axiom he calls the foundation of all science, the rule and measure of truth. The next step to be taken was to determine the rules for the proper detection of these ideas; and these rules he has laid down as follows: 1. Never accept anything as true but what is evidently so; to admit nothing but what so clearly and distinctly presents itself as true that there can be no reason to doubt it. 2. To divide every question into as many separate questions as possible; that each part being more easily conceived, the whole may be more intelligible--(Analysis). 3. To conduct the examination with order, beginning by that of objects the most simple, and therefore the easiest to be known, and ascending little by little up to knowledge of the most complex--(Synthesis). 4. To make such exact calculations and such circumspections as to be confident that nothing essential has been omitted. Consciousness, being the ground of all certainty, everything of which you are clearly and distinctly conscious must be true; everything which you clearly and distinctively conceive exists, if the idea of it involves existence.