He affirms that besides circular motion, which he holds to be simple and by which he proves that the heavens, which he assumes to move circularly, are a simple body, there are only two other simple motions, one downward, or from the circumference toward the center, the other upward, or from the center toward the circumference; that simple motion suits the simple bodies, and consequently that earth and fire are simple bodies, of which one is absolutely heavy and the other absolutely light.