The cosmos is divided into two parts. In the sphere of heavenly bodies everything is eternal and runs on unchangeable, perfect orbits; on the earth chance holds sway instead of mathematical laws. The boundary is the moon, the lowest of the heavenly bodies, which still runs on a mathematical orbit yet with changing light. This division of the world into a translunar and a sublunar realm is the common property of the Academy, even if it was Aristotle who had the deepest influence on later thought.