For everything that is at one time an agent actually, and at another time an agent in potentiality, needs to be moved by a mover. Now it is evident that the will begins to will something, whereas previously it did not will it. Therefore it must, of necessity, be moved by something to will it. And, indeed, it moves itself, as stated above (A. 3), in so far as through willing the end it reduces itself to the act of willing the means. Now it cannot do this without the aid of counsel: for when a man wills to be healed, he begins to reflect how this can be attained, and through this reflection he comes to the conclusion that he can be healed by a physician: and this he wills. But since he did not always actually will to have health, he must, of necessity, have begun, through something moving him, to will to be healed. And if the will moved itself to will this, it must, of necessity, have done this with the aid of counsel following some previous volition. But this process could not go on to infinity. Wherefore we must, of necessity, suppose that the will advanced to its first movement in virtue of the instigation of some exterior mover, as Aristotle concludes in a chapter of the Eudemian Ethics (vii, 14).
Reply Obj. 1: It is essential to the voluntary act that its principle be within the agent: but it is not necessary that this inward principle be the first principle unmoved by another. Wherefore though the voluntary act has an inward proximate principle, nevertheless its first principle is from without. Thus, too, the first principle of the natural movement is from without, that, to wit, which moves nature.
Reply Obj. 2: For an act to be violent it is not enough that its principle be extrinsic, but we must add "without the concurrence of him that suffers violence." This does not happen when the will is moved by an exterior principle: for it is the will that wills, though moved by another. But this movement would be violent, if it were counter to the movement of the will: which in the present case is impossible; since then the will would will and not will the same thing.
Reply Obj. 3: The will moves itself sufficiently in one respect, and in its own order, that is to say as proximate agent; but it cannot move itself in every respect, as we have shown. Wherefore it needs to be moved by another as first mover. ________________________
FIFTH ARTICLE [I-II, Q. 9, Art. 5]
Whether the Will Is Moved by a Heavenly Body?
Objection 1: It would seem that the human will is moved by a heavenly body. For all various and multiform movements are reduced, as to their cause, to a uniform movement which is that of the heavens, as is proved in Phys. viii, 9. But human movements are various and multiform, since they begin to be, whereas previously they were not. Therefore they are reduced, as to their cause, to the movement of the heavens, which is uniform according to its nature.
Obj. 2: Further, according to Augustine (De Trin. iii, 4) "the lower bodies are moved by the higher." But the movements of the human body, which are caused by the will, could not be reduced to the movement of the heavens, as to their cause, unless the will too were moved by the heavens. Therefore the heavens move the human will.
Obj. 3: Further, by observing the heavenly bodies astrologers foretell the truth about future human acts, which are caused by the will. But this would not be so, if the heavenly bodies could not move man's will. Therefore the human will is moved by a heavenly body.
On the contrary, Damascene says (De Fide Orth. ii, 7) that "the heavenly bodies are not the causes of our acts." But they would be, if the will, which is the principle of human acts, were moved by the heavenly bodies. Therefore the will is not moved by the heavenly bodies.