We have, then, on the one hand, the world of Ideas, on the other, matter, an absolutely formless, chaotic, mass. By impressing the images of the Ideas upon this mass, "things" arise, that is to say, the specific objects of sense. They thus participate both in Being and in not-being. But how is this mixing of Being and not-being brought about? How do the Ideas come to have their images stamped upon matter? It is at this point that we enter upon the region of myth. Up to this point Plato is certainly to be taken literally. He of course believed in the reality of the world of Ideas, and he no doubt also believed in his principle of matter. And he thought that the objects of sense are to be {210} explained as copies of the Ideas impressed upon matter. But now, with the problem how this copying is brought about, Plato leaves the method of scientific explanation behind. If the Ideas are the absolute ground of all things, then the copying process must be done by the Ideas themselves. They must themselves be made the principles for the production of things. But this is, for Plato, impossible. For production involves change. If the Ideas produce things out of themselves, the Ideas must in the process undergo change. But Plato has declared them to be absolutely unchangeable, and to be thus immutable is to be sterile. Hence the Ideas have within themselves no principle for the production of things, and the scientific explanation of things by this means becomes impossible. Hence there is nothing for it but to have recourse to myth. Plato can only imagine that things are produced by a world-former, or designer, who, like a human artist, fashions the plastic matter into images of the Ideas. God, the Creator, the world-designer, finds beside him, on the one hand, the Ideas, on the other, formless matter. First, he creates the World-Soul. This is incorporeal, but occupies space. He spreads it out like a huge net in empty space. He bisects it, and bends the two halves into an inner and an outer circle, these circles being destined to become the spheres of the planets and the stars respectively. He takes matter and binds it into the four elements, and these elements he builds into the empty framework of the World-Soul. When this is done, the creation of the universe is complete. The rest of the "Timaeus" is occupied with the details of Plato's ideas of astronomy and physical {211} science. These are mostly worthless and tedious, and we need not pursue them here. But we may mention that Plato, of course, regarded the earth as the centre of the world. The stars, which are divine beings, revolve around it. They necessarily move in circles, because the circle is the perfect figure. The stars, being divine, are governed solely by reason, and their movement must therefore be circular, because a circular motion is the motion of reason.