The motion of the subject itself is due to some agent.  And since every agent acts for an end, as was shown above (Q. 1, A. 2), the principle of this motion lies in the end.  And hence it is that the art which is concerned with the end, by its command moves the art which is concerned with the means; just as the “art of sailing commands the art of shipbuilding” (Phys. ii, 2).  Now good in general, which has the nature of an end, is the object of the will.  Consequently, in this respect, the will moves the other powers of the soul to their acts, for we make use of the other powers when we will.  For the end and perfection of every other power, is included under the object of the will as some particular good:  and always the art or power to which the universal end belongs, moves to their acts the arts or powers to which belong the particular ends included in the universal end.  Thus the leader of an army, who intends the common good—­i.e. the order of the whole army—­by his command moves one of the captains, who intends the order of one company.

On the other hand, the object moves, by determining the act, after the manner of a formal principle, whereby in natural things actions are specified, as heating by heat.  Now the first formal principle is universal “being” and “truth,” which is the object of the intellect.  And therefore by this kind of motion the intellect moves the will, as presenting its object to it.

Reply Obj. 1:  The passage quoted proves, not that the intellect does not move, but that it does not move of necessity.

Reply Obj. 2:  Just as the imagination of a form without estimation of fitness or harmfulness, does not move the sensitive appetite; so neither does the apprehension of the true without the aspect of goodness and desirability.  Hence it is not the speculative intellect that moves, but the practical intellect (De Anima iii, 9).

Reply Obj. 3:  The will moves the intellect as to the exercise of its act; since even the true itself which is the perfection of the intellect, is included in the universal good, as a particular good.  But as to the determination of the act, which the act derives from the object, the intellect moves the will; since the good itself is apprehended under a special aspect as contained in the universal true.  It is therefore evident that the same is not mover and moved in the same respect. ________________________

SECOND ARTICLE [I-II, Q. 9, Art. 2]

Whether the Will Is Moved by the Sensitive Appetite?

Objection 1:  It would seem that the will cannot be moved by the sensitive appetite.  For “to move and to act is more excellent than to be passive,” as Augustine says (Gen. ad lit. xii, 16).  But the sensitive appetite is less excellent than the will which is the intellectual appetite; just as sense is less excellent than intellect.  Therefore the sensitive appetite does not move the will.

Obj. 2:  Further, no particular power can produce a universal effect.  But the sensitive appetite is a particular power, because it follows the particular apprehension of sense.  Therefore it cannot cause the movement of the will, which movement is universal, as following the universal apprehension of the intellect.