Prime Mover Part 2: Who is the Prime Mover?

In my last post, I left off with a bit of a cliff hanger. In that article, I presented an ancient and sometimes overlooked (in the contemporary climate) argument for the existence of God, called the Prime Mover argument, or the argument from motion, which is Aquinas’ famous First Way. I argued in that post that the proof shows the existence of a being which is “Pure Act,” and I made the claim that this being is God. But why should we think that, if some being of Pure Act does in fact exist, this being is God, or even anything like God? For that matter, who is “God” anyways?

First, before I continue, let me give a very brief summary of the argument presented in the last post:

  1. Our experience via our senses observes that there exist objects/beings in motion
  2. Motion is a potency raised/reduced to act
  3. A potency can only be raised to act by another which is itself already in act
  4. Essentially ordered causal series of such motion cannot in principle have an infinite regress
  5. Therefore, there must exist a being who is Pure Act

What does it mean to be a being of Pure Act? Well, as its name quite obviously tells us, this being is purely actual, that is, it has no potencies able to be actualized. It is fully, totally, in act. It is an “unmoved mover,” the source and cause of all motion that we see here and now in existence. It is the first or “prime” mover.

This argument has been around for a very long time, and it has garnered a very large amount of responses/critiques/objections. In this post, I’ll examine some of the most common, frequently encountered objections. Here’s a preliminary list:

  1. Why think the being of Pure Act is God?
  2. In particular, why think the being of Pure Act is sentient/personal/conscious?
  3. Quantum physics has undermined the act/potency premises. Objects are seen to change randomly, without any sort of external cause.
  4. Newton’s laws of motion undermine the act/potency premises
  5. How does the unmoved mover move anything?

Now, before I begin my analysis of these objections, I’d like to point out that the popular “Crash Course” youtube channel has recently made a video on Aquinas’s Five Ways, including the First Way, which we are currently examining. I was rather pleasantly surprised/impressed that a youtube channel consisting of ten minute videos aimed at high school students would have a segment on Aquinas. Hank Green, who runs the video, was fair in his presentation, but ultimately I think he was uninformed. His video raised objections that wouldn’t (I hope) have been raised by anyone who has actually read/studied Aquinas and his supporters in depth. Still, you can’t ask for much from a ten minute video, and at least this helps get these ideas “out there,” as it were. The link to the video is here.

I’d like to use the video to start/build my analysis of common criticisms to the Prime Mover argument. First, Hank Green makes absolutely no reference to the act/potency distinction, which means that the argument is drastically misunderstood. The argument, again, isn’t just that things move, and nothing can move itself, so there must be something which moves everything else. The argument is rather based on the metaphysical principles of act and potency, which says that motion (change, in the modern sense), is a potency being actualized by something already actual. Green also makes the mistake of accusing Aquinas of rejecting all infinite regresses in general, which is simply false. If you remember my last post, I explained that Aquinas distinguishes between accidentally ordered causal series and essentially ordered causal series. Green makes the claim that “Aquinas was wrong in his insistence that there can’t be an infinite regress of anything.” Well, yes, Aquinas would be wrong if he ever actually said that, which he absolutely never did. In fact, Aquinas did contemplate the existence of certain types of infinite regresses, namely, those consisting of accidentally ordered causal series. Aquinas was willing to concede that, theoretically, an accidentally ordered causal series could go back infinitely, with no beginning. He was even willing, for the sake of argument, to assume that the universe itself might never have had a beginning, which makes Green’s next statement very ironic. He says, “Aquinas takes it as a given that there had to be a starting point for everything,” which, as I’ve just explained, isn’t true. Aquinas doesn’t take anything as a “given.” Instead, he offers detailed arguments for why an essentially ordered causal series cannot in principle have an infinite regress. The very definition of an essentially ordered series, as explained in the previous post, automatically precludes the possibility of an infinite regress. An example that philosopher Edward Feser uses (and others, as well), is that of a stick moving a rock. The rock cannot move itself (can’t actualize its own potential for movement), but the stick can move it (can actualize the potential of the rock for movement. I don’t think I need to keep explaining at this point what I mean by “move”). However, the stick cannot move itself either, a hand must move it. Now, imagine we had an infinitely long stick that was moving the stone. Would such a stick, so long that we cannot see the hand, somehow make it possible that there is no need for a hand? No, absolutely not. By virtue of the nature of the stick, and by virtue of the nature of such essentially ordered causal series, such “infinite” regresses are, in principle, impossible. Green laughingly calls this point about infinite regresses one of two “nails in the coffin” for the argument. Unfortunately, the nail has been stuck in the wrong coffin.

Green then explains what he sees as the “most significant charge leveled against Aquinas’s arguments,” which is that they’re somehow “self defeating,” that they “actually prove themselves wrong.” There’s actually an interesting approach that Green could have taken here, and which I will examine further on. Instead, he settles for perhaps the most egregious criticism of any argument for the existence of God ever offered: the “what caused God?” objection, made popular by Richard Dawkins and company. Green asks, if everything must be put in motion by something else, and nothing can move itself, shouldn’t God also be subject to this principle, thus requiring a mover for himself? Green actually directs this question towards the first four of Aquinas’s Five major arguments, the others of which I will be examining in future posts. For the prime mover argument, the answer is pretty much the same as it was above: Green is accusing Aquinas of committing an error for something which he never claimed. Aquinas never says that “everything must have a mover.” Aquinas does say that whenever a potential is actualized, it must be done by something already actual. Since the being of Pure Act (we haven’t actually confirmed that this being is God yet) by definition has no potencies, then the being of Pure Act by definition cannot be actualized by another being. In other words, the being of Pure Act must be the Prime, “unmoved,” mover. If the being of Pure Act could be so “moved,” then that would mean it has potencies, which would mean we’d just have to push the series back farther until we reached the actual being of Pure of Act. Green asks why, if God can be “exempt” from the premise, other beings can’t be as well, and if other beings can be exempt, why do we need God to explain them in the first place? But it is not that the being of Pure Act is “exempt” from the premise, it is that the being of Pure Act, by definition, does not fit into the principle in the first place.

Green’s major complaint, however, is one of the most common objections raised against the Prime Mover argument: that it doesn’t establish the existence of any “particular” God, that it doesn’t establish the existence of the Judeo-Christian God, or even a personal/sentient God at all. Then Green makes the really bizarre comment that “Aquinas’s argument doesn’t rule out polytheism, there’s nothing in any of his arguments to prove that there isn’t actually [many]” such “gods.” This comment, however, completely ignores crucial writings from Aquinas on the subject. First, before we go about establishing that the being of Pure Act is in fact “God,” I’d like to make several points about what the purpose of the argument actually is.

Aquinas was an absolutely prolific writer, and he wrote about everything from theology to metaphysics, psychology to ethics. He used five major arguments to establish the existence of God which are called the “Five Ways.” In the main work in which he expounded upon these Five Ways, Aquinas was writing to other Catholic priests who already believed in the existence of the Christian God. Aquinas did not use these arguments for any real sort of in depth “apologetic” to persuade/convert nonbelievers. So when Aquinas says that the being of Pure Act is what we call God, a modern critic might shout, “but wait, why should I think that?” Aquinas’s audience, however, already knew that the being of Pure Act was God, so he didn’t feel the need to further explain right then and there. However, he does go into much depth and detail later in other places, and these later extrapolations are often completely overlooked.

The Prime Mover argument seeks to establish the existence of a being of Pure Act. We’ve already seen that the argument does not make false assumptions about infinite regresses, and it is not trivially self defeating. So, if it is otherwise successful (we will be looking at other, more potent objections later), then we do indeed have a being of Pure Act which needs explaining. Is the being of Pure Act God?

Well, instead of thinking of it as a sort of “matching” game where we take our definition of “God” and try to line it up with the being of Pure Act, let’s rather start with the being of Pure Act and see what we can discover, necessarily, about its nature. In doing so, we will also be answering some other common objections to the argument as a whole.

First, we know that the being of Pure Act must necessarily be immutable. The very use of this word itself follows directly from the conclusion of the Prime Mover argument. From the latin immutabilis (in+mutabilis, where we also get the word motion) meaning, literally, unable to change or be changed. How do we know the being of Pure Act is immutable? Because if a being is able to undergo change, it must (as already previously discussed) have potencies which can be actualized, and if it has potencies, it is, by definition, not a being of Pure Act. A being of Pure Act has no potencies to be actualized, meaning it necessarily cannot undergo change. It is the unmoved mover. This is not some ad hoc construction pinned onto the end of the argument to make it support a prior definition of “God,”; this is a necessary fact that flows immediately and directly from the conclusion of the argument itself.

In the same way, we can also discover that the being of Pure Act is immaterial, timeless, omnipotent, etc. Each of these next attributes requires a bit more in depth examination, and can be done so in several ways.

How do we know the being of  Pure Act is immaterial? Because all material objects/beings are composites of act and potency, meaning all material objects/beings undergo change, which means no material objects can be Pure Act, which means that the being of Pure Act is necessarily immaterial. “Now, wait,” you might say. “Why should we think that all material objects are composites of act and potency?” Well, take, for example, a random material object such as, say, a regular old table. The table is actual, that is, it actually exists, here and now, as a table, and not as some other material object such as, say, a frog. But this table also has many potencies which are not actual. Let’s say that this particular table is actually brown. In that case, it is potentially any other color. Or let’s say the table is four feet tall, but I come in and saw off a foot from each leg. In that case, the table is potentially a different height than it is now. Likewise, the wood which makes up the table obviously has the potential to be many other objects besides a table. After all, the wood once belonged to a certain tree, and could be stripped from the table to make something else, such as a chair, or a picture frame. Or it could be used for firewood. The point is that as a material object, a table has a very large amount of potencies inherent to its essence.

But is this true for all material objects? It seems somewhat certain that it is, for being material just is being changeable. Consider a single hydrogen atom. If I were to add a proton, it would become a helium atom. Or consider the proton itself; it has the potential to be in any of the elements. An electron in a hydrogen atom has the potential to be in a higher or lower energy state. The subatomic particles have the potency to be rearranged in a plethora of different ways. The same is true for whatever the most basic particles of physical reality turn out to be; physical particles are malleable and mutable, they have the potential to be a part of an almost endless amount of material structures. Some particles make up planets, some stars, some comets, some black holes, some tables, some elephants, some humans. This is all to say that whatever the most fundamental structures of reality turn out to be, they will be absolutely full of potencies. So  “matter” and “energy” are about as far away from Pure Act as you can get. The being of Pure Act, therefore, being necessarily immutable, cannot be material, for to be material just is to be mutable, and full of potency.

It doesn’t help that modern cosmology has shown that all matter came into existence a finite amount of time ago, and, of course, to come into being is most definitely an instance of change. This brings us to our next point: the being of Pure Act must be timeless, or eternal. Consider, again, a single fundamental particle. This particle exists in time, and so it must have the potency to exist from moment to moment. The same is true for all particles, and all material objects that are within the bounds of time. All such objects have a potential to exist, and a potential to not exist (this is related to several other of Aquinas’s Five Ways, which I will be examining in future posts). So this potential to exist from moment to moment must be constantly actualized from moment to moment. Since to exist within time just is to have the potency to exist continuously actualized over time, the being of Pure Act must necessarily be outside of time, making the being of Pure Act timeless/eternal. You might ask why the being of Pure Act does not also have the potential to exist from moment to moment; but for any being which exists outside of time, it’s nonsensical to say that it exists in any “moment.” A being which exists outside of time doesn’t exist moment to moment, but rather just exists outside of all moments, eternally.

Similarly, the being of Pure Act must be one; there cannot be many such beings. Contrary to Hank Green and other critics, who charge that the argument doesn’t prove monotheism over polytheism, there can only in principle be one being of Pure Act. To show why this is the case, imagine two triangles drawn next to each other on a piece of paper. Imagine that the triangles are identical in every possible feature, their size, angle measurement, etc. But now imagine that the only difference between the two triangles is that one is blue, and the other is red. The triangles are different because of their distinct potencies for color which have been actualized. But even if both triangles were the exact same color, we could distinguish them because they take up different positions in space. Each triangle has the potential to be drawn on any position on the piece of paper; if both triangles were drawn in the exact same position on top of each other, we wouldn’t be able to tell the difference; it would appear to be just one triangle. What distinguishes the two triangles is that they each have a separate potency for position, or for color, that has been actualized. This is true for anything; we distinguish between beings based on unrealized potencies. But a being of Pure Act has no unrealized potencies by its very nature. If there were two beings of Pure Act, what would distinguish one from the other? If one being of Pure Act had more knowledge than the other, this would mean that one being of Pure Act had more fully actualized the potency for knowledge. But a being of Pure Act cannot in principle have any potency for knowledge that is not already fully actualized. If it did, it would not be a being of Pure Act after all. Thus the being of Pure Act must be one, which shows that Green’s “polytheism” comment is false.

Now, when it comes to the traditional “attributes” of God, such as omnipotence and especially omniscience, the conversation gets a bit tricky. In recent years, some philosophers have questioned whether these traditional attributes make sense at all, claiming that they are incoherent and inconsistent with each other. For our purposes now, it doesn’t matter much whether we call the being of Pure Act “omnipotent” or not; what matters is that we have established a being which is the cause of all motion in existence; the first, unmoved mover of everything. For the rest of this post, I will be using “omnipotence” just to refer to this fact.

The next significant challenge to the argument, offered by Green and many others, is that there’s no reason to think that the being of Pure Act is personal, sentient, or conscious. After all, so critics say, isn’t the God of the Bible described as personal and relational? How do we know that the being of Pure Act hears prayers, or cares about humans, or even consciously knows anything at all?

However, this objection is mostly irrelevant. Even if it were impossible to prove that the being of Pure Act is personal, the argument still wouldn’t fail, not even by a long shot. After all, even Aquinas differentiates between things which can be proven by reason alone, and things which require revelation to tell us, such as that God is a trinity. But think of it this way: suppose there was someone who already believed in the Christian God on separate, independent grounds other than the prime mover argument. This person believes in one, omnipotent, immaterial, eternal, immutable God who is also personal. Now suppose that this person encounters the prime mover argument, and comes to the conclusion that there exists a being of Pure Act who is also one, omnipotent, immaterial, eternal, and immutable, but not necessarily personal. It would be absurd for this person to conclude that there are two beings, each of which are one, omnipotent, immaterial, eternal, and immutable, but one of which is personal while the other is not (never mind that, as already shown, the being of Pure Act must be one). If the prime mover argument succeeds in proving the existence of a being of Pure Act, who has all the attributes which flow from being Pure Act, then one is surely justified in concluding that this being is “God,” whether or not you can prove in the same argument that being is also personal, or triune, or that the being has ever acted in history. There are other arguments which seek to establish those further things (indeed, another of Aquinas’s Five Ways does prove that this being must be personal), and the prime mover argument just cannot be judged as a “failure” because it does not prove every known thing about God.

With that being said, however, it is possible to show that the being of Pure Act is personal, although it is somewhat less clear than with the previous attributes. However, to explain this further attribute would take a large amount of time and space, and, seeing as how this post is already quite long, I think it best to end here. Although I wanted to finish the Prime Mover argument in two posts, I’m going to need at least a third to get through everything that needs to be said. So, in my next post I will be looking to do the following things: 1) Show that the being of Pure Act is personal, 2) Answer more complex objections, especially those relating to quantum physics and the act/potency distinction.

Until then, please continue to offer your own questions/criticisms, and I will be happy to respond!

Written by Harrison Jennings



I must acknowledge that for the vast majority of this post I am greatly indebted to the works of philosopher Edward Feser, who has opened my eyes on so much. While this article is in my own words, and includes my own thoughts and analyses, the central ideas come from the writings of Feser. These include his books (The Last Superstition, Aquinas, Scholastic Metaphysics) as well as his online blog.

Feser, Edward. The Last Superstition: A Refutation of the New Atheism. South Bend: St. Augustine’s Press, 2008. ebook.

Feser, Edward. Aquinas. London: Oneworld Publications, 2009.

9 thoughts on “Prime Mover Part 2: Who is the Prime Mover?

  1. Mr. Jennings,
    I read your last two posts on the prime mover argument with great interest because I have been studying Feser’s book The Last Superstition. I found nothing objectionable about the arguments, but he doesn’t make it clear to me how the immaterial and unmoving prime mover causes material things to move. I hope to see an explanation in your next post.
    Paul Buchman


    • Hi!

      Thank you for reading and responding to my posts! I must admit, when I first encountered this argument, I had the exact same question. You’re right that Feser doesn’t make it very clear in The Last Superstition, although he does comment a little on this issue in his book on Aquinas. I am addressing this question in my next post, which I am working on now! It should hopefully be completed by this weekend.

      The short answer has to do with our experience of motion. In our experience, anything that moves something else is itself moving. So if I move a stick, my hand has to move in order to move it, and my arm, which moves my hand, is itself moving, and so on. This is mostly because everything in our experience is bound by its material nature. The being of Pure Act, however, is not material, and so for it to cause motion does not necessitate that it itself be moving. As for how something immaterial can cause something material to move, that’s a bit tricky. The truth is that the “how” of it all may be beyond our ability to completely comprehend. Again, everything that we directly experience is material. The only motion we actually perceive is that of material objections affecting other material objects. We have no immaterial objects to directly observe, so it’s not exactly clear how the being of Pure Act causes motion; it is only clear that there must be a being of Pure Act who does in fact cause motion.

      Thanks again! If you have any further questions after my next post, I would love to try to help!


  2. Hello Harrison,
    “if both triangles were drawn in the exact same position on top of each other, we wouldn’t be able to tell the difference; it would appear to be just one triangle.” : so in this case, what (precisely which unactualized potency) would enable us to distinguish one triangle from another ?


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