Data collected about the stars led greeks to believe that the stuff past the moon was in some way special. Our world: dominated by earth, air, water, fire: powered by the heavens and their influence on us. Aristotle: universe is made up of a series of spheres. These spheres do not behave like earth: unchanging. Argument for unchanging spheres: (c1) not all changing things are able to be destructible: this would lead to absurdities like time being destructible. 4 causes: material, formal, final, and efficient. The unmoved mover is a final cause.