CT 4: The Immobility of God

Having shown that God exists, Thomas goes on to show that God is immobile, that is, that God is unchanging:

We clearly infer from this that God, who moves all things, must Himself be immovable. If He, being the first mover, were Himself moved, He would have to be moved either by Himself or by another. He cannot be moved by another, for then there would have to be some mover prior to Him, which is against the very idea of a first mover.

Recall that Thomas showed in chapter 3 that there must be a first mover, and that he equated this first mover with God. So if God is moved, that is, if He changes, He Himself must be the cause of the change. So far, so good.

If He is moved by Himself, this can be conceived in two ways: either that He is mover and moved according to the same respect, or that He is a mover according to one aspect of Him and is moved according to another aspect. The first of these alternatives is ruled out. For everything that is moved is, to that extent, in potency, and whatever moves is in act. Therefore if God is both mover and moved according to the same respect, He has to be in potency and in act according to the same respect, which is impossible.

When a thing changes, some potential of that thing is becoming actualized. The ball is here, but potentially it is there; if I move it there, then it is no longer potentially there, it is actually there. My eldest son is a boy, but potentially he is a man; in time (God willing) he will be one in actuality. This is true, according to Aristotle, of all change. So Thomas is saying that God is moving Himself “in the same respect” then He is both “in act” as the mover and “in potency” as the thing moved, and is therefore in act and in potency “in the same respect”, which is impossible.

I confess that I do not entirely understand what Thomas means by “in the same respect”. In the next bit, he speaks of God as having two parts, one part moving (i.e., causing the change) and the other moving (i.e., changing). So it’s possible that by “in the same respect” he means that the same part of God is both moving and moved. Also, while I can see why the thing moved is in potency, I can’t see why the mover is in act.

The second alternative is likewise out of the question. If one part were moving and another were moved, there would be no first mover Himself as such, but only by reason of that part of Him which moves. But what is per se is prior to that which is not per se. Hence there cannot be a first mover at all, if this perfection is attributed to a being by reason of a part of that being. Accordingly the first mover must be altogether immovable.

OK, this I can see. If God has two parts, one causing change and one being changed, then God isn’t really the first mover at all; rather, that part of God which is causing the change is the real first mover. I’m still puzzing over the line “…what is per se is prior to that which is not per se.”

Now, I’ve read somewhat further than this, and discovered that the translator has used the terms per se and per accidens to refer to a being’s essential and accidental features respectively. Something is essential if it cannot be changed, and accidental if it can be. Thus, a dog is a dog; its dogginess is an essential feature. If you changed it, you’d no longer have a dog. But the length of the dog’s coat is accidental. You can trim it, or the dog can shed it, and still have a dog, indeed, you still have the same dog. And I think that phrase I used, “if it cannot be changed,” is beginning to get at the heart of the matter. As God is the first mover, the fact that God is a mover, is a cause of change, is clearly per se, clearly essential. The notion that God is being moved by Himself is not essential, and so we can’t insist on it.

This indicates to me that God need not be moved; I’m not sure Thomas has shown that God can not be moved. But then, what we’ve got here in the Compendium aren’t full-fledged proofs, but rather brief sketches of arguments.

Among things that are moved and that also move, the following may also be considered. All motion is observed to proceed from something immobile, that is, from something that is not moved according to the particular species of motion in question, Thus we see that alterations and generations and corruptions occurring in lower bodies are reduced, as to their first mover, to a heavenly body that is not moved according to this species of motion, since it is incapable of being generated, and is incorruptible and unalterable. Therefore the first principle of all motion must be absolutely immobile.

This is a second sketch of an argument. I don’t know whether the principle Thomas cites, that “All motion is observed to proceed from something…that is not moved according to the particular species of motion in question,” is really valid apart from the Aristotelian notion of the heavenly bodies and their effects. It certainly seems unlikely, so I’ll not worry at this argument further. Clearly I should write something about alterations, generations, and corruptions, though, and that means I should write something about forms. Oh, joy!

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