3.1 Argument One
The first argument in SCG 1,13 is one that Aquinas takes himself to inherit from Aristotle’s Physics VII.3 It runs thus:
1. Everything that is moved is moved by another.4
2. Some things are obviously in motion (are moved) and are therefore moved by something else.
3. What moves something else is either moved or not moved.
4. If what moves something else is not moved, then there is an unmoved mover, which is what God is supposed to be.
5. If what moves something else is moved, it is moved by another mover.
6. There cannot be an infinite number of things moving other things while themselves being moved by other things.
7. So we must posit “some prime unmoved mover.”
This argument appears to be formally valid. But Aquinas immediately goes on to note that two propositions in it themselves need to be proved, namely (1) and (6). Before proceeding to an account of what he says in this connection, however, I should comment on what Aquinas means by “motion” or “movement,” for which his Latin word is motus.
I presume that most of us understand motion or movement chiefly to amount to local motion: the change that something undergoes as it changes place. So we would naturally say that cars move around when driven or that people move when they walk to work. But, of course, we also speak of being moved emotionally, which does not imply a reference to local motion. Also without thinking of local motion we can make sense of sentences like “Fred moved up in the company.” So, even we have a sense or senses of “move” where local motion is not in question, and, I now need to note, motus, for Aquinas, though it does sometimes refer to local motion, basically means what we would call “change.”
We speak of things changing their position. Yet we also speak of things changing in quality and quantity (as when John acquires a suntan or as when he puts on weight). So we can distinguish between change of place, change of quality, and change of quantity, all of which Aquinas would have taken to be instances of motus. We have motus, he thinks, as something is in process of changing from one place or state to another. Or, as he would have said, motus depends on something first being actually thus and so while able to become different, and the motus of something is the movement to the state arrived at. Aquinas analyzes motus in terms of what he calls “actuality” and “potentiality.” He thinks, for example, that if I am on the way to acquiring a suntan, then (1) I must first be actually nonsuntanned, and (2) I must be able to (have the potentiality to) become suntanned. Aquinas thinks of my ending up suntanned as a matter of my having arrived by a process of change from one state to a different one, and it is change in this sense that he is concerned with in SCG 1,13. He thinks of it as a process that some particular existing thing actually undergoes. If you fall in love with me, then I might be said to have become loved by you, and one might be tempted to think of this as a “real change” in me. But, of course, it is not. I can become loved by you without being modified in any respect and without even knowing about you. If anything is really changed as I become loved by you, it is you, and it is only “real change” in something that Aquinas is concerned with as he talks about motus, which he regards as a genuine modification that something undergoes, a genuine movement (i.e., process of change) in something.5
In his first SCG 1,13 argument, therefore, Aquinas, taking motion as obviously there to be observed in the world, thinks that it is something that has to be accounted for. He also thinks that it cannot be accounted for in terms of an endless series of movers.6
You may think that X’s motion is to be entirely attributed to X, that motion in something need not be motion due to something other than X. But proposition (1) in the above argument is stating that this is not so. As I have noted, however, Aquinas clearly thinks that the proposition “Everything moved is moved by another” needs defense, and he seeks to defend it by means of three arguments. You may immediately think that no defense is required here, for, you might say, if something is moved then it has to be moved by something else. “Moved” looks like a verb in the present passive form, unlike the intransitive “moves.” Is it not, therefore, obvious that if something is moved it is moved by something else? But this is not really obvious at all. I will be moved by myself if I punch myself in the face or feed myself. So it is not clear that if something is moved it is moved by something else, as Aquinas is aware.7
Let me, therefore, now report on his SCG arguments in defense of (1).
3.1.1 “Everything That Is Moved Is Moved by Another”
The first runs thus:
1. Something that moves itself has “within itself the principle of its own motion.”8 If it does not have the principle, or origin, of its own motion in itself, it is moved by something else.
2. Something moved by itself must also be “primarily moved” by itself. “It must be moved by reason of itself, and not by reason of a part of itself” since, if moved by a part of itself, “a whole would not be moved by itself, but a part, and one part would be moved by another.”9
3. Something moved by itself must also be divisible and have parts since “whatever is moved is divisible.”10
4. Nothing primarily moved is moved because of a part of itself moving while another part of itself is “at rest.” But “nothing that is at rest because something else is at rest is moved by itself” since “that being whose rest follows upon the rest of another must have its motion follow upon the motion of another” and is, therefore, not moved by itself.11
Aquinas immediately notes a possible objection to this argument. For might one not say that when something moves itself no part of it can be at rest? Yet, argues Aquinas, the force of the argument he is now defending lies in the fact that if something moves itself primarily, then there is no “other” involved, and certainly no moving part of itself involved, while the moving of divisible things depends on their parts. We do not, says Aquinas, have to presume in some “absolute” sense that “a part of a being moving itself is at rest.” But we should assume that if the part were at rest, the whole would be at rest.12 Evidently, Aquinas is here thinking that if something can be truly said to be thus and so by virtue of a part of it, then the thing as a whole, considered as an individual, can be said to be thus and so. He is thinking, for example, that if I have no hairs on my chest but a lot of hairs on my head and legs, I can be said to be hairy.
Aquinas’s second line of thought in defense of proposition (1), a line of thought that he calls “inductive,” amounts to a series of reinterpretations of counter examples that an objector might present as evidence against (1).13 He observes:
1. Something moved whose movement does not follow from what it is essentially or by nature is not moved by itself but by another.
2. What is moved by violence is not moved by itself.
3. What is moved by its nature, as animals, for example, are, is not moved by itself since all the movement of such things depends on a nature that they have but have not manufactured for themselves.
4. Heavy and light bodies move because of generating causes and causes removing impediments to them moving.14
The next argument in defense of (1) draws on the notions of actuality and potentiality. Perhaps it would be best for me to quote the argument in full rather than lay it out in stages. The argument reads:
The same thing cannot be at once in act and in potency with respect to the same thing. But everything that is moved is, as such, in potency. For motion is the act of something that is in potency inasmuch as it is in potency. That which moves, however, is as such in act, for nothing acts except according as it is in act. Therefore, with respect to the same motion, nothing is both mover and moved. Thus, nothing moves itself.15
The idea here is that if something is moving so as to become F, it cannot already be F. It is actually not F and is only able to become F. Aquinas is also saying that if something comes to be F, this can only be by virtue of something able to bring this about. It has been claimed that Aquinas is here falsely saying that what is not F can only be made to be F by something that is actually F. Hence, for example, Anthony Kenny, as if contradicting Aquinas, observes that “a kingmaker need not himself be king, and it is not dead men who commit murders.”16 Aquinas, however, is not denying any of this.
His reasoning seems to be (1) that what only potentially exists does not actually exist and cannot account for any actualizing of potentiality, and (2) the nonexisting F-ness of something, which, as nonexisting, does not exist in the thing, cannot be invoked to account for the thing’s coming to be F. Aquinas means that what a thing does not have is not something that can account for change that it undergoes and that, in this sense, nothing moves itself. In some places, Aquinas distinguishes between “univocal” and “equivocal” causes, between causes that are just like their effects and causes that produce effects without resembling them exactly.17 When thinking of efficient or agent causality, Aquinas’s view is that, since nothing can give what it does not have, there has to be a sense in which the effects of causes somehow show them forth or, if you like, resemble them. He does not, however, mechanically assume that cause X of effect Y looks like Y or is exactly like what Y is. If he assumed this, he would have to assume, as he does not, that God looks like grass because God accounts for the existence of grass. As John Wippel explains, Aquinas does not mean to suggest that something “must be or have formally that which it communicates to something else through motion. It must either be or have such formally, or else produce the characteristic virtually; this is to say, it must have the power to produce its effect.”18 So, the third SCG 1,13 argument has to be read as concluding that nothing moves itself since it does not have within itself the wherewithal to bring about in itself what it does not have to start with.
So now to proposition (6) in the first SCG 1,13 argument: “There cannot be an infinite number of things moving other things while themselves being moved by other things.” Why does Aquinas take this claim to be true?
3.1.2 “There Is No Procession to Infinity among Movers and Things Moved”
In SCG 1,13 Aquinas is arguing that there is a first unmoved mover. He claims that a series of things moved by others must terminate in what is not moved by anything else. But why should he think this? After all, we can keep counting without end. There is, presumably, no number beyond which there is no other number. So why should there be any end when it comes to movers moving? In defense of proposition (6), however, Aquinas offers three arguments.
The first is this:
1. Assuming that what is moved is material (and, therefore, divisible into parts), an infinite series of movers and things moved will be bodily (material).
2. Every body that moves something moved is itself moved while moving it.
3. So an infinite series of movers and things moved will itself have to be moved, considered as a whole, which means that all of the members of the series, considered as a whole, are moved if any of them are moved.
4. If one of the members is finite, however, it is moved in a finite time, which means that all of the infinite series of movers and things moved are moved in a finite time, which is impossible.
5. “It is, therefore, impossible that among movers and things moved one can proceed to infinity.”19
The second is this:
1. In “an ordered” series of movers and things moved, if the first mover is “removed or ceases to move” no other mover will move or be moved.
2. If movers and things moved went on infinitely, there would be no first mover and none of the others would be able to be moved and there would be nothing moved.
It is important to note that when he speaks of a series of movers and things moved that is “ordered” (ordinatus) Aquinas is not thinking of just any collection of movers and things moved. He is not, for example, thinking of a series of things moving and moved going back into the past infinitely: a series such as we would have if, say, I came to be because of movements of my parents, who came to be because of movements of their parents, who came to be because of movements of their parents, and so on without beginning. In SCG 2,35–38, Aquinas holds that one cannot demonstrate the impossibility of such a chronologically backwardly running series. He does the same in On the Eternity of the World (De Aeternitate Mundi), where he denies that it can be philosophically proved that the world had a beginning.20
So the above argument is not asserting that if X is moved by Y, and if Y is moved by Z, there has to be a temporally first mover accounting for this. Rather, Aquinas is saying that if movers X, Y, and Z are all equally dependent for their movement on something distinct from them as each of them moves, then there has to be a mover not dependent in the same way, a mover that accounts for the movement of X, Y, and Z considered as a unity.
Suppose that I kick a ball that hits another ball and pushes it along. Also suppose that the second ball hits another ball and moves that along, and so on, for as many balls as you care to think about. Clearly, I am not directly moving all the balls in the series. In this sense, the movement of all of them need not depend on me. Indeed, I could drop dead having kicked the first ball.
Now, however, consider a different scenario. I hold in the palm of my hand a book, on which rests another book, on which rests another and another. I then move my hand from left to right and back again. In this scenario, I am responsible for the movement of each of the books as it occurs, and it will stop occurring if I stop moving my hand on which the books rest. In this scenario, each book supporting the one above it is, so to speak, only an instrument of me. Remove me, and all the books crash to the ground since all of them depend on me moving my hand while they rest on it and move in space.
When he speaks of an ordered series, Aquinas is thinking of a series of movers like that in the hand/book scenario, not a series like the kicking of the balls one. His argument is that if such a series proceeded to infinity it would impossibly consist only of instrumental movers. Or, as Aquinas himself says: “If there are movers and things moved following an order to infinity, there will be no first mover, but all would be as intermediate movers.”21 As Aquinas goes on to observe, the same point can be made in reverse, starting with a first mover instead of a series of things moved by it. We read: “That which moves as an instrumental cause cannot move unless there be a principal moving cause. But, if we proceed to infinity among movers and things moved, all movers will be as instrumental causes, because they will be moved movers and there will be nothing as a principal mover.”22