The first and the fourth arguments may be termed cosmological proofs. They are based on the hypothesis that the series of causes for every change is finite, and terminates in the Primal Cause. There is no essential difference in the two arguments: in the first are discussed the causes of the motion of a moving object; the fourth treats of the causes which bring about the transition of a thing from potentiality to reality. To prove that neither the spheres nor a force residing in them constitute the Primal Cause, the philosophers employed two propositions, of which the one asserts that the revolutions of the spheres are infinite, and the other denies the possibility that an infinite force should reside in a finite object. The distinction between the finite in space and the finite in time appears to have been ignored; for it is not shown why a force infinite in time could not reside in a body finite in space. Moreover, those who, like Maimonides, reject the eternity of the universe, necessarily reject this proof, while those who hold that the universe is eternal do not admit that the spheres have ever been only potential, and passed from potentiality to actuality. The second argument is supported by the following supplementary proposition: If two elements coexist in a state of combination, and one of these elements is to be found at the same time separate, in a free state, it is certain that the second element is likewise to be found by itself. Now, since things exist which combine in themselves motive power and mass moved by that power, and since mass is found by itself, motive power must also be found by itself independent of mass. The third argument has a logical character: The universe is either eternal or temporal, or partly eternal and partly temporal. It cannot be eternal in all its parts, as many parts undergo destruction; it is not altogether temporal, because, if so, the universe could not be reproduced after being destroyed. The continued existence of the universe leads, therefore, to the conclusion that there is an immortal force, the Primal Cause, besides the transient world. These arguments have this in common, that while proving the existence of a Primal Cause, they at the same time demonstrate the Unity, the Incorporeality, and the Eternity of that Cause. Special proofs are nevertheless superadded for each of these postulates, and on the whole they differ very little from those advanced by the Mohammedan Theologians.