But it is clear enough that the crown of Aristotle's whole system is this "prime mover," "unmoved" and "apart from matter," and that this conception, up to which his thought leads from every side, as the necessary implication from the motion everywhere seen in the world, is his chief contribution to the argument for the existence of the Divine. Aristotle's chief interest lay in the cosmological problem, and his form of proof and the result which he reached by it were moulded by this fact. His argument did not lead him to a Creator of the world, for the universe, no less than the prime mover, was eternal, and the latter is nothing more than a principle of reason immanent in the world--pervading it, not distinguished from it--and the author of motion only in a passive way, after all, as a sort of magnetic object of desire.[20] In other places Aristotle makes passing references to different forms of the argument to prove the existence of the gods,[21] but it is evident that his own interest centered around this unmoved final cause, and it is in his proof of its existence from cosmological considerations that his significance for us lies. In the post-Aristotelian schools we have an entire change of the point of view, and instead of a philosophy of nature, such as occupied the attention of the pre-Socratic thinkers, or a philosophy of mind, such as Socrates, Plato, and to a large extent, Aristotle attempted to construct, we find the interest of men in speculative questions centered in a philosophy of life, of morals. Corresponding to this change in the point of view, we may easily detect an alteration in the manner of dealing with the arguments for the existence of the gods.