A History of Mediaeval Jewish Philosophy

by Isaac Husik

23. Whatever is potential and has in it a possibility may at some time not exist as an actuality.

24. Whatever is potential is necessarily possessed of matter, for possibility is always in matter.

25. The principles of an individual compound substance are matter and form; and there must be an agent, i. e., a mover which moves the object or the underlying matter until it prepares it to receive the form. This need not be the ultimate mover, but a proximate one having a particular function. The idea of Aristotle is that matter cannot move itself. This is the great principle which leads us to investigate into the existence of the first mover.

Of these twenty-five propositions, Maimonides continues, some are clear after a little reflection, some again require many premises and proofs, but they are all proved in the Physics and Metaphysics of Aristotle and his commentators. My purpose here is, as I said, not to reproduce the writings of the philosophers. I will simply mention those principles which we must have for our purpose. I must add, however, one more proposition, which Aristotle thinks is true and more deserving of belief than anything else. We will grant him this by way of hypothesis until we explain what we intend to prove. The proposition is:

26. Time and motion are eternal and actual. Hence there must be a body moving eternally and existing actually. This is the matter constituting the substance of the heavenly bodies. Hence the heavens are not subject to genesis and decay, for their motion is eternal. This presupposes the possibility of accidental infinity (cf. above, p. [251]). Aristotle regards this as true, though it does not seem to me that he claims he has proved it. His followers and commentators maintain that it is a necessary proposition and demonstrated. The Mutakallimun, on the other hand, think it is impossible that there should be an infinite number of states in succession (cf. ibid.). It seems to me it is neither necessary nor impossible, but possible. This is, however, not the place to discuss it.[273]

Now follows the classical proof of the existence of God from motion. It is in essence the same as that given by Ibn Daud, but much more elaborate. We shall try to simplify it as much as possible. The numbers in parentheses in the sequel refer to the preliminary propositions above given.

We start with something that is known, namely, the motion we see in the sublunar world, the motion which is involved in all the processes of genesis and decay and change generally. This motion must have a mover (25). This mover must have another mover to move it, and this would lead us to infinity, which is impossible (3). We find, however, that all motion here below ends with the motion of the heaven. Let us take an example. The wind is blowing through an opening in the wall. I take a stone and stop up the hole. Here the stone is moved by the hand, the hand by the tendons, the tendons by the nerves, the nerves by the veins, the veins by the natural heat, the natural heat by the animal soul, the animal soul by a purpose, namely, to stop the hole from which the wind comes, the purpose by the wind, the wind by the motion of the heavenly sphere. But this is not the end. The sphere must also have a mover (17). This mover is either outside the sphere it moves or within it. If it is something outside, it is either again a body like the sphere, or an incorporeal thing, a "Separate Intelligence." If the mover of the sphere is something within the sphere, two alternatives are again possible. The internal moving power of the sphere may be a corporeal force extended throughout the body of the sphere and divisible with it like heat, or an indivisible power like soul or intellect (10, 11). We thus have four possibilities in all. The mover of the heavenly sphere may be (a) a body external to the sphere; (b) a separate incorporeal substance; (c) an internal corporeal power divisible with the division of the sphere; (d) an internal indivisible power. Of these four, (a) is impossible. For if the mover of the sphere is another body, it is likewise in motion (9) and must have another to move it, which, if a body, must have another, and so on ad infinitum, which is impossible (2). The third hypothesis, (c), is likewise impossible. For as the sphere is a body it is finite (1), and its power is also finite (12), since it is divisible with the body of the sphere (11). Hence it cannot move infinitely (26). Nor can we adopt the last alternative, (d). For a soul residing within the sphere could not alone be the cause of continuous motion. For a soul that moves its body is itself in motion per accidens (6); and whatever moves per accidens must necessarily sometime stop (8), and with it the thing set in motion by it will stop also. There is thus only one alternative left, (b), viz., that the cause of the motion of the sphere is a "separate" (i. e., incorporeal) power, which is itself not subject to motion either per se or per accidens; hence it is indivisible and unchangeable (7, 5). This is God. He cannot be two or more, for "separate" essences which are not body are not subject to number unless one is cause and the other effect (16). It follows, too, that he is not subject to time, for there is no time without motion (15).

We have thus proved with one stroke God's existence as well as his unity and incorporeality. But, it will be observed, if not for the twenty-sixth proposition concerning the eternity of motion, which implies an infinite power, we should not have been forced to the alternative (b), and could have adopted (c) as well as (d). That is, we might have concluded that God is the soul of the heavenly sphere resident within it, or even that he is a corporeal force pervading the extension of the sphere as heat pervades an ordinary body. But we must admit that in this way we prove only the existence of a God who is the cause of the heavenly motions, and through these of the processes of genesis and decay, hence of all the life of our sublunar world. This is not the God of Jewish tradition, who creates out of nothing, who is the cause of the being of the universe as well as of its life processes. Maimonides was aware of this defect in the Aristotelian view, and he later repudiates the Stagirite's theory of eternal motion on philosophical as well as religious grounds. Before, however, we speak of Maimonides's attitude in this matter, we must for completeness' sake briefly mention three other proofs for the existence of God as given by Maimonides. They are not strictly Aristotelian, though they are based upon Peripatetic principles cited above and due to the Arabian commentators of Aristotle.

The second proof is as follows. If we find a thing composed of two elements, and one of these elements is also found separately, it follows that the other element is found separately also. Now we frequently find the two elements of causing motion and being moved combined in the same object. And we also find things which are moved only, but do not cause motion, as for example matter, or the stone in the last proof. It stands to reason therefore that there is something that causes motion without being itself subject to motion. Not being subject to motion, it is indivisible, incorporeal and not subject to time, as above.

The third proof is based upon the idea of necessary existence. There is no doubt that there are existing things, for example the things we perceive with our senses. Now either all things are incapable of decay, or all are subject to genesis and decay, or some are and some are not. The first is evidently untrue for we see things coming into, and passing out, of being. The second hypothesis is likewise untrue. For if all things are subject to genesis and decay, there is a possibility that at some time all things might cease to be and nothing should exist at all. But as the coming and going of individuals in the various species in the world has been going on from eternity, the possibility just spoken of must have been realized—a possibility that is never realized is not a possibility—and nothing existed at all at that moment. But in that case how could they ever have come into being, since there was nothing to bring them into being? And yet they do exist, as ourselves for example and everything else. There is only one alternative left, therefore, and that is that beside the great majority of things subject to genesis and decay, there is a being not subject to change, a necessary existent, and ultimately one that exists by virtue of its own necessity (19).