Having established that God is the cause that holds the rational agent in existence, it is now necessary to see to it that God’s causing and co-causation insofar as He is the Prime Creator of the will does not necessitate His determination of the will. The will is moved by an intrinsic principle belonging to the agent, viz. the intellect. This movement of the intellect towards truth and goodness directs the will because the will aims at goodness. But the will cannot be said of as being moved by the agent if it is moved by God. Therefore it is necessary to conclude that the will is moved by the agent and not by God:
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.
The human will is free insofar as every act that the human person wills is a voluntary act—even acts that are under coercion. Aquinas argues that there are two types of acts: the voluntary and the involuntary. Acts which are involuntary are intrinsic to the thing itself but are not willed by the agent since there is a lack of recognition of the good as object of the will (be this rational or irrational). On the other hand, the willing of an act is voluntary since the agent recognizes the good as known. In the human agent, the good as known directs the action voluntarily. But voluntary does not entail freedom, for, as Aquinas notes, freedom is the object of the will and can only be understood in light of reason.
It is necessary here to consider an objection to the nature of the will as I have proposed here. If, as argued above, the will is free and necessitated by a natural telos (end) to the Good as the intellect apprehends it, then it would mean that the will is not free to act insofar as it must act towards the ultimate Good in the face of the ultimate Good. In this way the will, while arguably freed from the coercion of God’s will, is still necessitated by its natural inclination. And if such a position is true then we must consider that in God’s creation of the will and its telos as such entails that God acts in the will immediately, thus negating its freedom.
The objection seems reasonable at first glance, but is invalidated at closer considerations of the objective and subjective dimensions of the will. Aquinas writes in his reply to the seventh objection in question six in De Malo:
An active principle moves necessarily only when it overcomes the power of the passive principle. But since the will is in potency to the good universally, no good overcomes the power of the will as necessarily moving it, except that which is good according to every consideration, and this is the perfect or complete good alone, i.e., happiness, which the will cannot will, that is, in such a way that it will the opposite; nevertheless the will can actually not will happiness because the will can turn away, i.e., avoid thinking about happiness inasmuch as the will moves the intellect to its act, and to this extent neither does the will necessarily will happiness itself, just as a person would not necessarily become warm if he could repel heat from himself when he willed.
The distinction made here, and what Aquinas points to, is the particularity of the goods of the soul. Where the objective aspect of voluntary act is the reality of the good toward which the desire of the will is inclined, the subjective dimension is the possession of such reality. As Aquinas writes, the will is directed towards a universal good, but such goods are participations and consequently are particular. As such, the reflective power of the intellect on the good [as particular] allows for the will to reconsider even the perfect good.
Another consideration of the freedom of the will as being caused by God only in the manner that he is the immediate cause of the agent’s being arises from the argument of evil actions. According to Aquinas, the will is the faculty of love and desire which acts directly at the apprehension of the intellect. The intellect, however, may at times mistake a non-good as a good. The apprehension which belongs internally to the agent is itself auto-causing, thus it is not God which is the source of this mistake. Further, God cannot be said of as sinning for “someone is the cause of sin in two ways: in one way because he himself sins, in another way because he causes another to sin. Neither of which can belong to God.” In the first way, God cannot be said as sinning because of the attribution of His nature free from the defect which sin requires for its existence. In the second way God cannot cause other to sin since sin is essentially the turning away from the calling to the ultimate end which is all-good. Yet, God is the very End towards which the will is called. Therefore, it violates the law of noncontradiction that one is both the cause of goodness and sin at the same time.
Conclusively, it seems that while human actions have as their authors both God and the human subject, the human subject acts freely. From what has been said in the past three posts, God is said as the cause of human acts only insofar as He is the reason for the human author’s existence at any given time—contrary to Durandus’ objection. As the cause and the One to keep the human agent’s being in existence, God is attributed with the human act, but this does not mean that he himself is the actor. For one can speak of co-causality in two ways. In the first, co-causation can be said of as two actors causing a certain effect in which without either one of the actors the effect cannot take place. For example, let us consider two men who are carrying a casket. The two are co-causes in the effect of the casket being moved, and without either one, the casket cannot move in the same way as it is moving when the two are carrying it. In the second way, co-causation can happen in the sense that one’s being is dependent upon the other directly and simultaneously that any act one does is attributed to the other as well. Consider for example an imperfect analogy of a human agent and a machine that is necessary to keep him living. We can attribute the human agent’s actions to the machine only insofar as without the machine the person would cease to live and therefore no actions are possible. Yet the human person’s actions are not dictated by the machine, but by the person himself. It is in this latter sense that God is said as an immediate cause in human actions for it is He whom the human person is dependent on for his existence at any given time.
 Summa Theologiae, II, 1, 9, a1, Corpus
 Summa Theologiae, II, 1, 10, a4, Corpus
 Summa Theologiae, II, 2, 6, a1, Corpus
 Ibid. if a thing has no knowledge of the end, even though it have an intrinsic principle of action or movement, nevertheless the principle of acting or being moved for an end is not in that thing, but in something else, by which the principle of its action towards an end is not in that thing, but in something else, by which the principle of its action towards an end is imprinted on it.
 Ibid. But those things which have a knowledge of the end are said to move themselves because there is in them a principle by which they not only act but also act for an end. And consequently, since both are from an intrinsic principle, to wit, that they act and that they act for an end, the movements of such things are said to be voluntary: for the word “voluntary” implies that their movements and acts are from their own inclination.
 This is evident in Aquinas noting that evil does not have a per se cause since no one aims at committing evil.
 The existence of sin is not ontological per se but is only in contrast to the lack of goodness in the action itself or is an accidental effect of the action.