…
Remotely there is one cause, and this cause is God. I will deal only with the latter part of that proposition here. God moves the free will, and He moves it according to its nature, which is to say freely. We can note that the way God moves things – that is, distributes actuality to them – is according to their nature. God moves an animal in a manner fitting to the animal. The animal has the potentials it does because of its form, which is to say the kind of thing it is. The kind of thing a deer is gives it the potential to run, and to do other deer-like things. It does not give the deer the potential to fly, or to jump over very large buildings. That is not to say it is impossible that the deer fly (in an airplane) or to jump over very large buildings (from the top of scaffolding), but only that the unaided form of a deer does not provide the potencies for such things. Potency is not
simply “logical possibility” but more fundamentally an ontological feature of formal causality, or simply “form.”
Now, the potential for a deer to walk is directed at actually walking. When the potential for the deer to walk is actualized, the deer actually walks. This is called final causality, or “teleology.” A potency is
for specific effects (in deterministic causality) or
for possible a range of effects (in non-deterministic causality, as we saw in the free will having multiple options presented to it by the intellect). When the deer’s potency to walk is actualized, it does not result in, say, the deer painting an exact replica of the Mona Lisa. Neither does such a potency, when actualized, result in the deer sitting, nor flying a kite. Certain potencies are directed towards certain actualities; otherwise it will not be a potency for anything, and will not actually result in anything in particular, viz., it will have no effect towards which it is directed, or will act at random.
Similar to how we say the intellect provides final causes for the will, which then sets about to actualize those final causes accordingly, we can say by analogy that final causality provides final causes for God’s will, which then sets about at actualizing those final causes accordingly. The actuality that the deer ultimately receives from God when it walks is apportioned to its potency, which is a potency for walking. Thus, the act that the deer receives is the act of walking. Now, the Thomist would also say that the form and thus the the teleology of the deer is found principally in the divine intellect, and only secondly in the deer itself; the latter is founded upon the prior, not the prior upon the latter. (Of course, this doesn’t mean that the divine intellect is the form of the deer any more than someone’s intellect is the form of a deer when they think about a deer; the form in such cases merely has cognitional being.) So, if we were to complete the analogy, the divine will moves the deer accordingly “because” of the divine intellect, which has and cognizes the form, and thus the potencies, and thus the teleology in the first place. And thus the proposition “God moves things according to their nature” is simply to say that God’s will acts upon creatures as an efficient cause according to the teleology He knows He gives them.
Now, the free will has the potential to various acts, but it acts in a free mode. Even if the will is a composite of potency and act such that the will can move itself by actualizing its potencies with other actualities it has, the actualities must ultimately receive their act from God, who is pure act; for composition of act and potency derives its act from pure act. …
(I’m not going to prove that exhaustively here; it deals with
per se series of efficient causes. Short version: (I) Being a composite entails having parts; (II) parts are potential to a whole; (III) Such a potential, if actualized, requires an external efficient cause; (IV) If that external efficient cause is not simply pure act, then such an external efficient cause is actual at a given moment is an actualized potency, for the efficient cause is not a necessary being but a potential one; (V) There cannot be an infinite regress providing the efficient cause its actuality [This would be like plugging a lamp into an infinite series of power strips with no generator and expecting the lamp to light up]; (VI) Therefore, pure act must provide actuality to any composites.)
… Thus, God provides the actuality of any of the free will acts, even if He does so in a way according to the free will’s form, potencies, and teleology, viz., freely. God provides the will the actuality to choose, and the will chooses from the potentials provided by the intellect. The will directs itself towards the actions which it determines, even if the actuality for doing so is derived from God.
Free-will is the cause of its own movement, because by his free-will man moves himself to act. But it does not of necessity belong to liberty that what is free should be the first cause of itself, as neither for one thing to be cause of another need it be the first cause. God, therefore, is the first cause, Who moves causes both natural and voluntary. And just as by moving natural causes He does not prevent their acts being natural, so by moving voluntary causes He does not deprive their actions of being voluntary: but rather is He the cause of this very thing in them; for He operates in each thing according to its own nature.
S.T. Ia Q.83, Art. 1, Ad. 3