wo ways: first, with regard to
acting and not acting; secondly, with regard to this or that action.
Thus the sight sometimes sees actually, and sometimes sees not: and
sometimes it sees white, and sometimes black. It needs therefore a
mover in two respects, viz. as to the exercise or use of the act, and
as to the determination of the act. The first of these is on the part
of the subject, which is sometimes acting, sometimes not acting:
while the other is on the part of the object, by reason of which the
act is specified.

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 ex