Motion, according to the PDBB, is the change from potency to act. To move something is to change that thing from potency to act. To be moved is to be changed from potency to act. Now, whatever is moved is put in motion by another. If that which moves another is itself moved, the latter needs a being to put it in motion. These are two interconnected propositions that stem from the division of being into potency and act. Now, potency is that which potentially is something, while act is what is actually something. Whatever goes from potentially being something to actually being something achieves this change by having that potency made actual by something already in act. That which is potential cannot actualize itself, ie. bring itself into being, for the reason that it is only potential and not actual. Only actual beings have power to effect any type of action.
The great expositors of this foundational tenet of the PDBB – Thomas Aquinas and Aristotle – made a shocking discovery: If there is no first mover, then there is no motion. But there is motion. So there must be a first mover, which is understood to be God.
Can this idea that motion requires that there exists a first mover be justified? There are indeed certain relations among beings that allow a thing to be ‘in act’ independent of a cause. For instance, we are all conceived of a man and a woman. They are the ones that bring us from potentially being to actually being, from possibly being to actually being. Yet, if our parents cease to exist, we can continue exist beyond them. Many other examples can be given to this effect.
However, this does not explain why beings, that exist only potentially, actually exist. The son does indeed continue to exist when his parents die, but that does not explain why he has being per se, or in himself. It only explains that he has being independent of his parents. More generally, it explains that things that per se potentially exist can have existence independent of other beings that per se potentially exist. A potentially existing being – a being that per se potentially exists, as opposed to per se actually existing – will only exist because actual being provides what is actual to the potentially existing being. A potentially existing being doesn’t lose its nature as a per se potentially existing being and become a per se actually existing being simply because its potency has been made actual. Think of the matter and form illustration from the PDBB article. Matter of itself potentially exists and actually exists when it manifests a form. The forms of themselves potentially exist and actually exist when instantiated in a given modicum of matter. Potential existence defines the very nature of both categories of being. For of itself, potency and all potentially existing beings don’t exist unless made actual – by something actual. If all that existed were potentially existing beings, there would be no beings because nothing would exist to bring what is potential to act.
These are propositions that stem from the potency/act distinction. In order for potency to be actually, it needs something actual to make it so. All beings that go from potency to act are, per se, potentially existing beings. Thus, something actual is needed to give actual existence to all that per se potentially exists.
To understand a different way, let’s make a graphic. I’m a computer illiterate, so bear with me. Draw three circles in a row, with plenty of space between each. Draw a line between the 1st and 2nd and the 2nd and 3rd. Inside each circle, but a ‘P’ on the left side and a ‘R’ on the right side. These stand for beings going from potency to act, the line being the power that shifts the potency into act. Potency is made actual by an actual being, hence why the line is next to the ‘A’. The ‘P’ is on the left side to represent that actual beings that go from potency to act only potentially have this act, only potentially exist. Potentially existing beings thus have derived act; they get their being from an actual being. A potentially existing being may derive its being, its act, from a potentially existing being, but the latter itself needs to be ‘activated’, or else it won’t have any ability to give the former being its act. If all beings were those that had being derivatively, there would be no being because there would be nothing to derive being from. Nothing would exist.
There must thus be a being, itself not moved from potency to act, that moves all else from potency to act. This being must furthermore be unmovable, because if it were possible for it to be not actual, it would be potential, since the only other kind of being is potency, as opposed to act. It would furthermore not be capable per se of any ability to move and belong ‘in the same boat’ as all the other potentially existing beings. It is this that we speak of when we speak of God.
Bare in mind that God is not as a being that kicks over a domino to start the movements of all other beings without any further action from Him. As this shows, all per se potentially existing beings need Him to actualize their potencies right now, because potency of itself never loses the necessity to be made actual in order for it to exist. All potentially existing beings that exist right now need His power of act in order for them to exist.
Based on this analysis, what is God? God is Pure Act, lacking potency. Since ‘act’ is ‘to be’ and God is Act Itself, He is not limited by potency or the necessity of motion to exist. For God to be does not mean to be something, such as a cat or a star. To potentially be is to potentially be a cat or a star or some particular kind of being. Indeed, one can’t speak of potency without referring to a specific kind of act. To classify a being as such is to limit it to some way of being, excluding from it other ways of being. However, God isn’t limited to any particular way of being, but is Being Itself. He contains within Him all ways of being, but isn’t restricted to any of them. Since we’ve seen that God is required for the existence of what per se potentially exists, it follows that all beings other than God have their being from God in they way that they have it. A potential being’s potential for being x is established by God. In other words, God determines the kind of being that something is.
Works consulted: Feser, Edward. “Natural Theology.” Aquinas: A Beginner’s Guide. Oxford: Oneworld, 2009. N. pag. Print.
magnificatanimameadominum1987 