Once the Ideas had been brought into mutual relation and shown to be compounded with one another, the task of connecting them with the external world became considerably easier; and the same intermediary which before had linked them to it as a participant in the nature of both, was now raised to a higher position and became the efficient cause of their intimate union. Such is the standpoint of the _Philêbus_, where all existence is divided into four classes, the limit, the unlimited, the union of both, and the cause of their union. Mind belongs to the last and matter to the second class. There can hardly be a doubt that the first class is either identical with the Ideas or fills the place once occupied by them. The third class is the world of experience, the Cosmos of early Greek thought, which Plato had now come to look on as a worthy object of study. In the _Timaeus_, also a very late Dialogue, he goes further, and gives us a complete cosmogony, the general conception of which is clear enough, although the details are avowedly conjectural and figurative; nor do they seem to have exercised any influence or subsequent speculation until the time of Descartes. We are told that the world was created by God, who is absolutely good, and, being without jealousy, wished that all things should be like himself. He makes it to consist of a soul and a body, the former constructed in imitation of the eternal archetypal ideas which now seem to be reduced to three—Existence, Sameness, and Difference.[157] The soul of the world is formed by mixing these three elements together, and the body is an image of the soul. Sameness is represented by the starry sphere rotating on its own axis; Difference by the inclination of the ecliptic to the equator; Existence, perhaps, by the everlasting duration of the heavens. The same analogy extends to the human figure, of which the head is the most essential part, all the rest of the body being merely designed for its support. Plato seems to regard the material world as a sort of machinery designed to meet the necessities of sight and touch, by which the human soul arrives at a knowledge of the eternal order without;—a direct reversal of his earlier theories, according to which matter and sense were mere encumbrances impeding the soul in her efforts after truth.