questions have been decided, does Levi ben Gerson undertake to give us his views of the constitution of the universe and the nature and attributes of God. In this discussion he takes occasion to express his dissatisfaction with Aristotle's proofs of the existence of the spheral movers and of the unmoved mover or God, as inadequate to bear the structure which it is intended to erect upon them. It will be remembered that the innovation of Abraham Ibn Daud and Maimonides in making Jewish philosophy more strictly Aristotelian than it had been consisted in a great measure in just this introduction of the Aristotelian proof of the existence of God as derived from the motions of the heavenly bodies. Levi ben Gerson's proofs are teleological rather than mechanical. Aristotle said a moving body must have a mover outside of it, which if it is again a body is itself in motion and must have a mover in turn. And as this process cannot go on ad infinitum, there must be at the end of the series an unmoved mover. As unmoved this mover cannot be body; and as producing motion eternally, it cannot be a power residing in a body, a physical or material power, for no such power can be infinite. Gersonides is not satisfied with this proof. He argues that so far as the motions of the heavenly bodies are concerned there is no reason why a physical power cannot keep on moving them eternally. The reason that motions caused by finite forces in our world come to a stop is because the thing moved is subject to change, which alters its relation to its mover; and secondly because the force endeavors to move the object in opposition to its own tendency, in opposition to gravity. In the case of the heavenly bodies neither of these conditions is present. The relation of the mover to the moved is always the same, since the heavenly bodies are not subject to change; and as they are not made of the four terrestrial elements they have no inherent tendency to move in any direction, hence they offer no opposition to the force exerted upon them by the mover. A finite power might therefore quite conceivably cause eternal motion. Similarly an unmoved mover cannot be body, to be sure, but it may be a physical power like a soul, which in moving the body is not itself moved by that motion. Aristotle's proofs therefore are not sufficient to produce the conviction that the movers of the spheres and God himself are separate Intelligences. 349
Gersonides accordingly follows a different method. He argues
