Dmitry Chernikov’s Blog

I have written that “the first way seems to be a special case of the second way“. That may have been premature. Now Aquinas writes that “motion is nothing else than the reduction of something from potentiality to actuality.” (ST, I, 2, 3) The most important thing to do in considering this argument is to forget everything about uniform motion. It confuses things greatly. And I still deny that uniform motion is an act opposed to the potency of rest (or vice versa). So, let us deal then solely with act and potency as such. “Thus that which is actually hot,” St. Thomas goes on, “as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it.” This is an excellent example, because it has nothing to do with uniform motion.

Now the potential is not yet, and what is not yet cannot act. Any becoming, any process, any movement from potentiality to actuality, therefore, cannot happen by itself but requires something already in the state of actuality to effect it. Thus, if O₁ is moving from state p to state a, then either (1) a part of its essence which is actual is producing this change in the part of its essence which is potential or (2) an external object-in-act is producing it. Considering (1), in the case of self-moving agents like humans, they can change themselves, e.g. by acquiring habits. The will, by which we move ourselves and which is in act, is different from our habits, which are in potentiality. On the other hand, as an example of (2), a body at rest cannot accelerate on its own; some other body must strike it or in some other way act in order to cause a change in its velocity. Let the will or that body be called O₂.

The question now is, is O₂ itself in the process of becoming? If it is, then it requires some O₃ to actualize it. But we cannot go to infinity in this process of actualization and must finally reach an object which “has become” or which is pure being without a trace of becoming in it.

Now we start running into problems. First, there is the existence of closed chains of movers. Let O_i be a thing with actuality A_i and potentiality x_i capable of mutating into actuality Y_i for an arbitrary i:

Here A₂ causes a move from x₁ to Y₁; …; A_n causes a move from x_n-1 to Y_n-1, and also A₁ causes a move from x_n to Y_n.

A different kind of closed chain occurs if the process of x_i → Y_i itself moves x_i-1 → Y_i-1. Suppose that A is actually hot and heats B which is potentially hot, whereas B is actually cold and cools A which is potentially cold. A changes B, and B, A. (From the point of view of physics only A will be considered actual, of course, because it has energy, while B is potential to receiving energy. But for our concerns such distinctions are not important.) In both cases there is no place for a prime mover.

Alright, let’s put this aside by saying that closed chains of movers tell us little about God, but what of open chains? The second problem is that there is a difference between an object which is not becoming at this moment and an object which cannot, in principle, become and which must needs therefore be pure act without any admixture of potentiality in it. In other words, we would like to demonstrate that there exists an n such that O_n is not merely accidental pure act which just happens to have nothing to actualize whatever potentialities are still within it, but rather an essential pure act which cannot change. Unfortunately, given our resources so early in our discussion of God, I don’t think we can. Aquinas himself is being extremely modest here: the prime mover is “put in motion by no other”; it’s not that it can be put in motion by no other. It seems that what we have is a piece of negative theology: if A is moving, then it is not God. But the reverse does not hold: something may not be in motion, yet it need not necessarily be God. God is thereby distinguished from all changing things.

What is so special about motion that God must be lacking it? Again, we want to complete the universe. To do so it is necessary to postulate an unchanging — though not, at this early stage of substantive speculation on God, unchangeable — source of change. (This means that God can evaporate by being put into motion by something prior; we cannot tell.) And this leads us to problem #3: our O_n is the source of actualities O₁ – O_n-1. But there may be numerous such chains of movers. Which chain is terminated by the one true God? We can only hope that subsequent investigation into the nature of God will reveal more.

Update. And it does, e.g., here.

Update 2. But no thing within the universe is stationary relative to all things; certainly not relative to all abstract coordinate systems. Pick any arbitrary object, and you will find it moving relative to something. Hence God must be outside the physical universe. Hence also God cannot be in space. Nor can He be a composite body, because one part of that body could always be put in motion relative to other parts. We’re moving quickly towards the Thomistic God.