Surely motion has a source, says Aristotle; and if we are not to plunge drearily into an infinite regress, putting back our problem step by step endlessly, we must posit a prime mover unmoved (primum mobile immotum), a being incorporeal, indivisible, spaceless, sexless, passionless, changeless, perfect and eternal. God does not create, but he moves, the world; and he moves it not as a mechanical force but as the total motive of all operations in the world;
