Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider the manner in which the will is moved. Under this head there are four points of inquiry:
(1) Whether the will is moved to anything naturally?
(2) Whether it is moved of necessity by its object?
(3) Whether it is moved of necessity by the lower appetite?
(4) Whether it is moved of necessity by the exterior mover which is God?
Objection 1: It would seem that the will is not moved to anything naturally. For the natural agent is condivided with the voluntary agent, as stated at the beginning of Phys. ii, 1. Therefore the will is not moved to anything naturally.
Objection 2: Further, that which is natural is in a thing always: as "being hot" is in fire. But no movement is always in the will. Therefore no movement is natural to the will.
Objection 3: Further, nature is determinate to one thing: whereas the will is referred to opposites. Therefore the will wills nothing naturally.
On the contrary, The movement of the will follows the movement of the intellect. But the intellect understands some things naturally. Therefore the will, too, wills some things naturally.
I answer that, As Boethius says (De Duabus Nat.) and the Philosopher also (Metaph. v, 4) the word "nature" is used in a manifold sense. For sometimes it stands for the intrinsic principle in movable things. In this sense nature is either matter or the material form, as stated in Phys. ii, 1. In another sense nature stands for any substance, or even for any being. And in this sense, that is said to be natural to a thing which befits it in respect of its substance. And this is that which of itself is in a thing. Now all things that do not of themselves belong to the thing in which they are, are reduced to something which belongs of itself to that thing, as to their principle. Wherefore, taking nature in this sense, it is necessary that the principle of whatever belongs to a thing, be a natural principle. This is evident in regard to the intellect: for the principles of intellectual knowledge are naturally known. In like manner the principle of voluntary movements must be something naturally willed.
Now this is good in general, to which the will tends naturally, as does each power to its object; and again it is the last end, which stands in the same relation to things appetible, as the first principles of demonstrations to things intelligible: and, speaking generally, it is all those things which belong to the willer according to his nature. For it is not only things pertaining to the will that the will desires, but also that which pertains to each power, and to the entire man. Wherefore man wills naturally not only the object of the will, but also other things that are appropriate to the other powers; such as the knowledge of truth, which befits the intellect; and to be and to live and other like things which regard the natural well-being; all of which are included in the object of the will, as so many particular goods.
Reply to Objection 1: The will is distinguished from nature as one kind of cause from another; for some things happen naturally and some are done voluntarily. There is, however, another manner of causing that is proper to the will, which is mistress of its act, besides the manner proper to nature, which is determinate to one thing. But since the will is founded on some nature, it is necessary that the movement proper to nature be shared by the will, to some extent: just as what belongs to a previous cause is shared by a subsequent cause. Because in every thing, being itself, which is from nature, precedes volition, which is from the will. And hence it is that the will wills something naturally.
Reply to Objection 2: In the case of natural things, that which is natural, as a result of the form only, is always in them actually, as heat is in fire. But that which is natural as a result of matter, is not always in them actually, but sometimes only in potentiality: because form is act, whereas matter is potentiality. Now movement is "the act of that which is in potentiality" (Aristotle, Phys. iii, 1). Wherefore that which belongs to, or results from, movement, in regard to natural things, is not always in them. Thus fire does not always move upwards, but only when it is outside its own place. [*The Aristotelian theory was that fire's proper place is the fiery heaven, i.e. the Empyrean.] And in like manner it is not necessary that the will (which is reduced from potentiality to act, when it wills something), should always be in the act of volition; but only when it is in a certain determinate disposition. But God's will, which is pure act, is always in the act of volition.
Reply to Objection 3: To every nature there is one thing corresponding, proportionate, however, to that nature. For to nature considered as a genus, there corresponds something one generically; and to nature as species there corresponds something one specifically; and to the individualized nature there corresponds some one individual. Since, therefore, the will is an immaterial power like the intellect, some one general thing corresponds to it, naturally which is the good; just as to the intellect there corresponds some one general thing, which is the true, or being, or "what a thing is." And under good in general are included many particular goods, to none of which is the will determined.
Objection 1: It seems that the will is moved, of necessity, by its object. For the object of the will is compared to the will as mover to movable, as stated in De Anima iii, 10. But a mover, if it be sufficient, moves the movable of necessity. Therefore the will can be moved of necessity by its object.
Objection 2: Further, just as the will is an immaterial power, so is the intellect: and both powers are ordained to a universal object, as stated above (A[1], ad 3). But the intellect is moved, of necessity, by its object: therefore the will also, by its object.
Objection 3: Further, whatever one wills, is either the end, or something ordained to an end. But, seemingly, one wills an end necessarily: because it is like the principle in speculative matters, to which principle one assents of necessity. Now the end is the reason for willing the means; and so it seems that we will the means also necessarily. Therefore the will is moved of necessity by its object.
On the contrary, The rational powers, according to the Philosopher (Metaph. ix, 2) are directed to opposites. But the will is a rational power, since it is in the reason, as stated in De Anima iii, 9. Therefore the will is directed to opposites. Therefore it is not moved, of necessity, to either of the opposites.
I answer that, The will is moved in two ways: first, as to the exercise of its act; secondly, as to the specification of its act, derived from the object. As to the first way, no object moves the will necessarily, for no matter what the object be, it is in man's power not to think of it, and consequently not to will it actually. But as to the second manner of motion, the will is moved by one object necessarily, by another not. For in the movement of a power by its object, we must consider under what aspect the object moves the power. For the visible moves the sight, under the aspect of color actually visible. Wherefore if color be offered to the sight, it moves the sight necessarily: unless one turns one's eyes away; which belongs to the exercise of the act. But if the sight were confronted with something not in all respects colored actually, but only so in some respects, and in other respects not, the sight would not of necessity see such an object: for it might look at that part of the object which is not actually colored, and thus it would not see it. Now just as the actually colored is the object of sight, so is good the object of the will. Wherefore if the will be offered an object which is good universally and from every point of view, the will tends to it of necessity, if it wills anything at all; since it cannot will the opposite. If, on the other hand, the will is offered an object that is not good from every point of view, it will not tend to it of necessity. And since lack of any good whatever, is a non-good, consequently, that good alone which is perfect and lacking in nothing, is such a good that the will cannot not-will it: and this is Happiness. Whereas any other particular goods, in so far as they are lacking in some good, can be regarded as non-goods: and from this point of view, they can be set aside or approved by the will, which can tend to one and the same thing from various points of view.
Reply to Objection 1: The sufficient mover of a power is none but that object that in every respect presents the aspect of the mover of that power. If, on the other hand, it is lacking in any respect, it will not move of necessity, as stated above.
Reply to Objection 2: The intellect is moved, of necessity, by an object which is such as to be always and necessarily true: but not by that which may be either true or false---viz. by that which is contingent: as we have said of the good.
Reply to Objection 3: The last end moves the will necessarily, because it is the perfect good. In like manner whatever is ordained to that end, and without which the end cannot be attained, such as "to be" and "to live," and the like. But other things without which the end can be gained, are not necessarily willed by one who wills the end: just as he who assents to the principle, does not necessarily assent to the conclusions, without which the principles can still be true.
Objection 1: It would seem that the will is moved of necessity by a passion of the lower appetite. For the Apostle says (Rom. 7:19): "The good which I will I do not; but the evil which I will not, that I do": and this is said by reason of concupiscence, which is a passion. Therefore the will is moved of necessity by a passion.
Objection 2: Further, as stated in Ethic. iii, 5, "according as a man is, such does the end seem to him." But it is not in man's power to cast aside a passion once. Therefore it is not in man's power not to will that to which the passion inclines him.
Objection 3: Further, a universal cause is not applied to a particular effect, except by means of a particular cause: wherefore the universal reason does not move save by means of a particular estimation, as stated in De Anima iii, 11. But as the universal reason is to the particular estimation, so is the will to the sensitive appetite. Therefore the will is not moved to will something particular, except through the sensitive appetite. Therefore, if the sensitive appetite happen to be disposed to something, by reason of a passion, the will cannot be moved in a contrary sense.
On the contrary, It is written (Gn. 4:7): "Thy lust [Vulg. 'The lust thereof'] shall be under thee, and thou shalt have dominion over it." Therefore man's will is not moved of necessity by the lower appetite.
I answer that, As stated above (Q[9], A[2]), the passion of the sensitive appetite moves the will, in so far as the will is moved by its object: inasmuch as, to wit, man through being disposed in such and such a way by a passion, judges something to be fitting and good, which he would not judge thus were it not for the passion. Now this influence of a passion on man occurs in two ways. First, so that his reason is wholly bound, so that he has not the use of reason: as happens in those who through a violent access of anger or concupiscence become furious or insane, just as they may from some other bodily disorder; since such like passions do not take place without some change in the body. And of such the same is to be said as of irrational animals, which follow, of necessity, the impulse of their passions: for in them there is neither movement of reason, nor, consequently, of will.
Sometimes, however, the reason is not entirely engrossed by the passion, so that the judgment of reason retains, to a certain extent, its freedom: and thus the movement of the will remains in a certain degree. Accordingly in so far as the reason remains free, and not subject to the passion, the will's movement, which also remains, does not tend of necessity to that whereto the passion inclines it. Consequently, either there is no movement of the will in that man, and the passion alone holds its sway: or if there be a movement of the will, it does not necessarily follow the passion.
Reply to Objection 1: Although the will cannot prevent the movement of concupiscence from arising, of which the Apostle says: "The evil which I will not, that I do---i.e. I desire"; yet it is in the power of the will not to will to desire or not to consent to concupiscence. And thus it does not necessarily follow the movement of concupiscence.
Reply to Objection 2: Since there is in man a twofold nature, intellectual and sensitive; sometimes man is such and such uniformly in respect of his whole soul: either because the sensitive part is wholly subject to this reason, as in the virtuous; or because reason is entirely engrossed by passion, as in a madman. But sometimes, although reason is clouded by passion, yet something of this reason remains free. And in respect of this, man can either repel the passion entirely, or at least hold himself in check so as not to be led away by the passion. For when thus disposed, since man is variously disposed according to the various parts of the soul, a thing appears to him otherwise according to his reason, than it does according to a passion.
Reply to Objection 3: The will is moved not only by the universal good apprehended by the reason, but also by good apprehended by sense. Wherefore he can be moved to some particular good independently of a passion of the sensitive appetite. For we will and do many things without passion, and through choice alone; as is most evident in those cases wherein reason resists passion.
Objection 1: It would seem that the will is moved of necessity by God. For every agent that cannot be resisted moves of necessity. But God cannot be resisted, because His power is infinite; wherefore it is written (Rom. 9:19): "Who resisteth His will?" Therefore God moves the will of necessity.
Objection 2: Further, the will is moved of necessity to whatever it wills naturally, as stated above (A[2], ad 3). But "whatever God does in a thing is natural to it," as Augustine says (Contra Faust. xxvi, 3). Therefore the will wills of necessity everything to which God moves it.
Objection 3: Further, a thing is possible, if nothing impossible follows from its being supposed. But something impossible follows from the supposition that the will does not will that to which God moves it: because in that case God's operation would be ineffectual. Therefore it is not possible for the will not to will that to which God moves it. Therefore it wills it of necessity.
On the contrary, It is written (Ecclus. 15:14): "God made man from the beginning, and left him in the hand of his own counsel." Therefore He does not of necessity move man's will.
I answer that, As Dionysius says (Div. Nom. iv) "it belongs to Divine providence, not to destroy but to preserve the nature of things." Wherefore it moves all things in accordance with their conditions; so that from necessary causes through the Divine motion, effects follow of necessity; but from contingent causes, effects follow contingently. Since, therefore, the will is an active principle, not determinate to one thing, but having an indifferent relation to many things, God so moves it, that He does not determine it of necessity to one thing, but its movement remains contingent and not necessary, except in those things to which it is moved naturally.
Reply to Objection 1: The Divine will extends not only to the doing of something by the thing which He moves, but also to its being done in a way which is fitting to the nature of that thing. And therefore it would be more repugnant to the Divine motion, for the will to be moved of necessity, which is not fitting to its nature; than for it to be moved freely, which is becoming to its nature.
Reply to Objection 2: That is natural to a thing, which God so works in it that it may be natural to it: for thus is something becoming to a thing, according as God wishes it to be becoming. Now He does not wish that whatever He works in things should be natural to them, for instance, that the dead should rise again. But this He does wish to be natural to each thing---that it be subject to the Divine power.
Reply to Objection 3: If God moves the will to anything, it is incompatible with this supposition, that the will be not moved thereto. But it is not impossible simply. Consequently it does not follow that the will is moved by God necessarily.