We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
Having now established that God is infinite, and having distinguished between this and a purely mathematical notion of infinity, Thomas now goes on to say what it means for God to be infinite.
The further inference is drawn that God is infinite in power. For power is consequent upon a thing’s essence; anything whatever possesses a power of activity consonant with its manner of being. Therefore, if God is infinite in His essence, His power must be infinite.
Any thing whatsoever can do whatever it does by virtue of what it is. An unsupported boulder can “seek” the lowest point and crush the car waiting there by virtue of being a large mass of stone. A dog can chase a cat by virtue of being an animal capable of locomotion. A human being can write a novel or a poem by virtue of being rational. The higher the essence, the greater the power. God’s essence is infinite, and hence God must be infinite in power.
Having made this bare statement, Thomas goes on to support it by reflecting on act and potency.
This is clear to anyone who will inspect the order of things. Whatever is in potency, is thereby endowed with receptive and passive power; and so far as a thing is in act, it possesses active power.
Hence what is exclusively in potency, namely, prime matter, has an unlimited power of receptivity, but has no part in active power.
Prime matter is a difficult concept; it doesn’t mean things made of atoms, or even atoms by themselves. Prime matter is what’s left when you remove all of the actuality from something: pure potency, pure receptivity, the power to become. When I eat an apple, the substance of the apple is assimilated by my body and becomes part of my body. What it is has changed. For Aristotle, there must be something that stands under any kind of change, something that remains unchanged; and for substantial change, something becoming something entirely different, that something is called prime matter.
You might say that prime matter is something like zero in arithmetic: there’s nothing there, but O what an important nothing it is.
But Thomas’ point is that in any being you can see a proportion between act and potency; and that being has active power insofar as it is in act, and is receptive of power insofar as it is in potency. If you reduce act to zero, leaving only potency, then in the limit you get prime matter, pure receptivity. And if, on the other hand, you reduce potency to zero and increase act to infinity, as with God, then you get pure (and infinite) power:
And in the scale of being above matter, the more a thing has of form, the more it abounds in the power of acting. This is why fire is the most active of all the elements. Therefore God, who is pure act without any admixture of potency, infinitely abounds in active power above all things.
In short, then, Thomas has now shown that not only does God exist, God is also omnipotent.