Here the necessity arises of investigating into the properties of motion, the moving agent and the thing moved. But this has already been explained sufficiently; and the opinion of Aristotle may be expressed in the following proposition: Matter does not move of its own accord—an important proposition that led to the investigation of the Prime Motor (the first moving agent).
Of these foregoing twenty-five propositions some may be verified by means of a little reflection and the application of a few propositions capable of proof, or of axioms or theorems of almost the same force, such as have been explained by me. Others require many arguments and propositions, all of which, however, have been established by conclusive proofs partly in the Physics and its commentaries, and partly in the Metaphysics and its commentary. I have already stated that in this work it is not my intention to copy the books of the philosophers or to explain difficult problems, but simply to mention those propositions which are closely connected with our subject, and which we want for our purpose.
To the above propositions one must be added which enunciates that the universe is eternal, and which is held by Aristotle to be true, and even more acceptable than any other theory. For the present we admit it, as a hypothesis, only for the purpose of demonstrating our theory. It is the following proposition:—
Proposition XXVI.
Time and motion are eternal, constant, and in actual existence.
In accordance with this proposition, Aristotle is compelled to assume that there exists actually a body with constant motion, viz., the fifth element. He therefore says that the heavens are not subject to genesis or destruction, because motion cannot be generated nor destroyed. He also holds that every motion must necessarily be preceded by another motion, either of the same or of a different kind. The belief that the locomotion of an animal is not preceded by another motion, is not true; for the animal is caused to move, after it had been in rest, by the intention to obtain those very things which bring about that locomotion. A change in its state of health, or some image, or some new idea can produce a desire to seek that which is conducive to its welfare and to avoid that which is contrary. Each of these three causes [[149]]sets the living being in motion, and each of them is produced by various kinds of motion. Aristotle likewise asserts that everything which is created must, before its actual creation, have existed in potentiâ. By inferences drawn from this assertion he seeks to establish his proposition, viz., The thing that moves is finite, and its path finite; but it repeats the motion in its path an infinite number of times. This can only take place when the motion is circular, as has been stated in Proposition XIII. Hence follows also the existence of an infinite number of things which do not co-exist but follow one after the other.
Aristotle frequently attempts to establish this proposition; but I believe that he did not consider his proofs to be conclusive. It appeared to him to be the most probable and acceptable proposition. His followers, however, and the commentators of his books, contend that it contains not only a probable but a demonstrative proof, and that it has, in fact, been fully established. On the other hand, the Mutakallemim try to prove that the proposition cannot be true, as, according to their opinion, it is impossible to conceive how an infinite number of things could even come into existence successively. They assume this impossibility as an axiom. I, however, think that this proposition is admissible, but neither demonstrative, as the commentators of Aristotle assert, nor, on the other hand, impossible, as the Mutakallemim say. We have no intention to explain here the proofs given by Aristotle, or to show our doubts concerning them, or to set forth our opinions on the creation of the universe. I here simply desire to mention those propositions which we shall require for the proof of the three principles stated above. Having thus quoted and admitted these propositions, I will now proceed to explain what may be inferred from them.
CHAPTER I
According to Proposition XXV., a moving agent must exist which has moved the substance of all existing transient things and enabled it to receive Form. The cause of the motion of that agent is found in the existence of another motor of the same or of a different class, the term “motion,” in a general sense, being common to four categories (Prop. IV.). This series of motions is not infinite (Prop. III.); we find that it can only be continued till the motion of the fifth element is arrived at, and then it ends. The motion of the fifth element is the source of every force that moves and prepares any substance on earth for its combination with a certain form, and is connected with that force by a chain of intermediate motions. The celestial sphere [or the fifth element] performs the act of locomotion which is the first of the several kinds of motion (Prop. XIV.), and all locomotion is found to be the indirect effect of the motion of this sphere; e.g., a stone is set in motion by a stick, the stick by a man’s hand, the hand by the sinews, the sinews by the muscles, the muscles by the nerves, the nerves by the natural heat of the body, and the heat of the body by its form. This is undoubtedly the immediate motive cause, but the action of this immediate cause is due to a certain design, e.g., to bring a stone into a hole by striking against it with a stick in order to prevent the draught from coming through the crevice. The motion of the air that causes the draught is the effect of the motion of [[150]]the celestial sphere. Similarly it may be shown that the ultimate cause of all genesis and destruction can be traced to the motion of the sphere. But the motion of the sphere must likewise have been effected by an agent (Prop. XVII.) residing either without the sphere or within it; a third case being impossible. In the first case, if the motor is without the sphere, it must either be corporeal or incorporeal; if incorporeal, it cannot be said that the agent is without the sphere; it can only be described as separate from it; because an incorporeal object can only be said metaphorically to reside without a certain corporeal object. In the second case, if the agent resides within the sphere, it must be either a force distributed throughout the whole sphere so that each part of the sphere includes a part of the force, as is the case with the heat of fire; or it is an indivisible force, e.g., the soul and the intellect (Props. X. and XI.). The agent which sets the sphere in motion must consequently be one of the following four things: a corporeal object without the sphere; an incorporeal object separate from it; a force spread throughout the whole of the sphere; or an indivisible force [within the sphere].