Prime Mover Part 3: Final Objections

This is the third and (hopefully) final post concerning the famous Prime Mover argument for the existence of God. In the first post I set forth the argument and claimed that it established the existence of a “being of Pure Act.” In the second post I responded to some common objections, and also explained why the being of Pure Act is “God,” in that the being of Pure Act must be one, immaterial, timeless, omnipotent, and immutable. I also claimed that it is somewhat irrelevant whether or not the Prime Mover argument alone is sufficient to establish that this being of Pure Act is personal. If such a being exists, who is purely actual, immaterial, timeless, omnipotent, and immutable, that is at least enough to prove false non theistic world views such as atheism and naturalism.

But besides this, I also made the comment that it is possible to show that the being of Pure Act is personal, although it is admittedly a bit less clear than with other attributes. In this final post, then, I’d like to accomplish the following: 1) show that the being of Pure Act is indeed personal, and 2) respond to more in depth, complicated objections to the argument.

The first argument used to show that the being of Pure Act is “personal” claims that all immaterial beings must be personal. In order to understand this claim, we first need to understand a bit of the underlying metaphysics. For Aristotle and Aquinas, all objects have a “form,” or an essence/nature, that which makes the object what it is. All material objects are “hylomorphic,” which just means that they are composites of form and matter, much like, as I discussed in the previous post, all material objects are also composites of act and potency. So, for example, a tree just is the form/essence/nature of a tree instantiated in the particular particles of matter which make up that tree.

Now, as should be clear, all material objects can only possibly have one form at any given moment in time. How could a tree possibly have the form of some other object such as, say, a crocodile, at the same time it has the form of the tree? For an object to change forms just is for the object to change to some other object. If I were to break down a chair and take the wood to make a table, the matter which makes up the chair would lose the form of a chair, and gain or become instantiated with the new form of a table.

But now consider the human mind. For Plato, “forms” actually exist on their own, independently of any instantiation of such forms in matter. In fact, for Plato, material instantiations of forms are less real than the forms themselves, mere shadows. For Aristotle, however, and then for Aquinas, forms are real only either in the objects in which they exist, or as abstractions from those objects in some mind which “grasps” that abstract idea of the form. So the form of, say, a kangaroo, doesn’t exist in some vague “world of forms” independently of the actual world; rather, the form of kangaroo only exists in real, actual kangaroos, and in any mind which thinks about/contemplates/understands kangaroos. When I conceive of a triangle, I am “grasping” the form of a triangle. The form, in a sense, exists, or is instantiated in, my mind. This means that the human mind cannot be a material object, for to be a material object is to only be capable of ever instantiating one form at a time, whereas the human mind quite obviously instantiates many forms, the forms of whatever it is capable of thinking/conceiving of (this last point gets into philosophy of mind, which will be a subject of a future post).

This seems to indicate that any immaterial object, by virtue of not being hylomorphic and thus not having the restraints of matter, would be capable of instantiating, theoretically, an infinite amount of forms. Since the being of Pure Act is necessarily immaterial, and is indeed the “most fundamental” immaterial being in that it actualizes all other potencies for existence, it would seem that, just like the human mind, the being of Pure Act must be “personal” in the sense of having the ability to “conceive of” different forms.

But, in addition to this, there is actually another, clearer way to show that the being of Pure Act is personal, although it too rests on an understanding of underlying metaphysical principles. For Scholastic philosophers, the Principle of Proportionate Causality entails that an effect of a cause must be proportionate to that cause. In the words of philosopher Edward Feser, “whatever is in the effect must in some sense be contained in the cause as well…a cause cannot give to its effect what it does not have to give” (Feser, The Last Superstition). As an example, imagine you come across a fire in the middle of a forest. You would rightly conclude that this fire had been caused to come about in some way,  and that it did not just randomly pop into existence without any cause; but there are several different ways in which it could have come about. One way is that a different, already existent fire could have caused this fire to exist, either by say, a spreading wildfire, or someone carrying a torch who used that torch to ignite a pile of sticks. In this case, the cause would be said to contain the effect “formally.” Another way, however, is that someone came along and used a match to start the fire. In this case, though the cause of the fire does not actually contain fire itself, it does have the power to create fire. Thus, the cause contains the effect “eminently.” If the cause did not contain the effect in one of these ways, the effect would be impossible, and the fire would not exist ((Feser, The Last Superstition).

Now, when we are considering the cause of things in the world, and in particular when we are considering the cause of human beings and human personhood, the principle of proportionate causality requires that our cause have our attributes either formally or eminently. Our attributes just are different powers or potentialities that we have due to our nature as human beings, and these attributes include our “personhood.” Now, if our attributes are just potentialities that we have, and if every potentiality must ultimately be made actual by the being of Pure Act, then the being of Pure Act is ultimately the “cause” of our attributes. This indicates that the being of Pure Act must also share our attributes, at least analogically.

No doubt a good deal of confusion will arise at this claim. After all, certain humans have attributes that surely we wouldn’t even want to say that God has: such as being evil, or being physically defective, or even just something trivial, such as smelling bad. In addition, if the being of Pure Act is necessarily immaterial, as we have shown, how could it be said to contain the material attributes that humans have, such as being short or tall, having skin, etc. Well, as said above, it is not the case that the being of Pure Act must actually contain all these physical attributes formally, but rather only that he must contain these attributes eminently; that is to say, that even if the being of Pure Act does not actually possess all of the attributes which humans do, he must at least have the power to produce such attributes. In the case of attributes such as moral deficiency, this is what is called a “negative” feature, or a “privation.” Moral evil is not an actual attribute in its own right; rather, it is the lack, or absence, or deficiency of an actual, positive attribute, namely moral uprightness (if you want to know why this is, just ask in the comments below and I’ll explain). In the case of attributes which only exist due to our physical, material nature, the being of Pure Act could only be said to contain these in the sense of having the power to create matter and material beings. Humans have other attributes, however, which are not material, such as morality and personhood. These the being of Pure Act could be said to contain formally; that is, not just having the power to create them, but actually possessing the same attributes, albeit analogically. In this way we can show that the being of Pure Act must possess a moral nature as well as personhood (let it be known that the idea of “personhood” is extremely complex and debated. Here, I am taking personhood to mean what Aquinas meant by it, that is, having intellect and will. This topic will be discussed further in a later post).

So finally we have established the existence of one being of Pure Act who is immaterial, immutable, timeless/eternal, omnipotent, and personal; and this being we can rightly, finally, call God.

But now let’s backtrack a little bit. For the most part, the objections to the prime mover argument that I’ve examined so far have dealt with the conclusion of the argument, that a being of Pure Act exists, and these objections I’ve looked at so far have been some of the most popular/common objections to the argument. I’d now like to look at a few, much more complicated, in depth objections. The first one again concerns the being of Pure Act. This objection states that the very idea of an unmoved mover is incoherent. Next, I’ll look at objections having to do with quantum mechanics. These last objections will be aimed not at the being of Pure Act, but rather the basic metaphysical principles themselves.

The first sort of objection claims that an “unmoved mover” is a logically incoherent idea in itself, on par with a “married bachelor,” even if not quite so blatantly inconsistent. After all, in our experience, everything which “moves” something else must itself be moved. A baseball bat can’t swing and hit a baseball unless it is swung by a person. This is, in fact, one of the main premises of the argument to begin with; that whatever is moved must be moved by another being already in act. The point is that no objects in our experience have an inherent power to move themselves or other objects, and yet objects are moved, thus the need for some being which does have the inherent power to move other objects. Baseball bats don’t swing themselves, brooms don’t stand up by themselves and magically sweep the floor; unless, of course, we’re in Disney’s Fantasia. But even in Fantasia, the brooms weren’t actually sweeping by themselves, they had been enchanted to do so by a magician. Even in our fantasies we cannot escape this intuitive metaphysical principle.

So how does the the unmoved mover actually move? The issue is that the premise states that “a potency can only be raised to act by another which is already in act.” But a being of Pure Act has no potencies able to be actualized. In our experience, everything that is moved, is moved by something which is itself moved, and etc. The Prime Mover argument was originally created not as a proof for God as Aquinas used it, but rather as just Aristotle’s attempt to explain all motion that we perceive. A being of Pure Act must exist to explain this motion. So is it possible for a being to move other objects without itself being moved, even though we don’t perceive such a being in our experience of motion? Emphatically, it is not only possible, it is necessary. Otherwise, there would be no such motion. We haven’t perceived such a being just because that being is the source and cause of all motion that we do perceive.

“But wait,” you might ask, “if motion is a potency raised to act, then wouldn’t the being of Pure Act have a potency if it changes from not moving to moving?” In other words, in order for the being of Pure Act to move anything, wouldn’t it have to go from a state of not causing motion, to a state of causing motion? And wouldn’t this change of states be itself a case of motion that needs explaining? The problem is that such a question assumes a temporal framework, whereas, as we have seen, the being of Pure Act is necessarily timeless. In our experience, all motion does exist within time. When I swing a baseball bat to hit a baseball, the motion exists in a temporal sequence. The bat goes from not swinging, to swinging, over a period of time. Also, this swinging happens relative to spatial position, because it is made of matter. For the bat to swing is just for the bat to change its spatial location. But the being of Pure Act is outside of time, space, and matter, and thus such frameworks just don’t apply. The being of Pure Act never goes from a state of not causing something, to a state of causing something, because such change of states is a temporal sequence. Rather, the being of Pure Act is outside of time, causing motion within time.

Take, for example, the beginning of the physical universe. Assuming that standard Big Bang models are correct (which is a totally separate, irrelevant issue), our universe had a beginning a finite amount of time ago. The way some people conceptualize the creation of the universe is that God had just existed for eternity past, and then, all of the sudden, bam! he created the universe; thus God was not creating for an eternity past, and then he started creating, which means he “changed” from not creating to creating. But again, this conceptualization just doesn’t work for a being that is outside time. It’s just meaningless to say that God “started” creating, or even to say that God has “always been” creating, because such concepts are intrinsically temporal. God can cause and affect motion that happens within time, and such motion does require an actual mover; but God himself exists outside of time as a purely actual being, and thus he himself never changes or undergoes motion. It would be like saying that in order for God to be the ultimate cause of a baseball bat swinging, God himself would have to move spatially, from one location to another. But God is immaterial and thus non-spatial, and its just nonsensical to say that he moves “from one location to another.” The argument says that all motion is potency raised to act, and that all potency can only be actualized by another already in act. But the argument nowhere states that a “mover” must itself be moved; it just so happens that all “movers” in our experience are secondary movers which themselves undergo motion and require external movers, and this series must terminate in one, unmoved mover, who is a primary rather than a secondary mover. Nothing has the power to move in itself except for this being of Pure Act, and all other beings derive their motion from this being alone.

To take an example that might work better for another of Aquinas’s Five Ways, but nonetheless fits here, think of the relationship between the moon and the sun. The moon is our second brightest source of light here on earth. But the moon does not actually possess any light in itself; it does not have the power to shine on its own. Rather, the moon reflects light from the sun, which does have the power in itself to give off light. Now, imagine a world where the moon didn’t directly reflect the sun’s light, but instead reflected the light from another moon. And this second moon, in turn, reflected the light from a third moon, and so on. Imagine that the only light that ever reached this world was from a series of thousands of moons, each reflecting the light from another moon. Even if we could not directly see the sun from this world, we would still know that there must be a sun, because moons, by their very nature, do not have the power to give off their own light. There must be a source of all the light. People from this world might wonder, “how is it possible for the sun to give off light without itself reflecting light from another source? All the sources of light in our experience only reflect light from other sources?” In the same way, we might wonder how a being could exist that moves other objects without itself being moved. We may not know exactly “how” this being does so, but we do know that such a being must exist, because all objects that we perceive are like moons; they are only secondary movers, which don’t have the power to move on their own, but only derive their motion from other moving objects. The Prime Mover is, in effect, the sun; the source of all motion.

The next, and final, objection, however, challenges this notion that all objects in our experience are secondary movers and can only be moved by other beings. In effect, it challenges the premise that “a potency can only be raised to act by another that is already in act.” If you recall, in my first post I provided several examples to support this premise: the changing of leaves, the playing of a piano, an animal walking, etc. In all of these examples there is an essentially ordered causal series in which every instance of motion is caused by another object already in act. But the objection is raised that the discoveries of quantum mechanics show that this premise is faulty. After all, doesn’t quantum mechanics show that at the subatomic level, changes occur randomly, without any external cause?

There are several ways of going about answering this objection. The first is to point out the difference between physics and metaphysics. Many who argue that discoveries of physics, such as quantum mechanics, undermine metaphysical principles, do so with at least an implicit assumption of scientism. Scientism is the belief that only science can give us real knowledge about the world, which is blatantly and obviously false (for many, many reasons, one of which being simply that scientism itself is a philosophical belief, not a scientific discovery/demonstration, thus undermining itself). I hope to address scientism in a future post, but until then, I will direct you to an article by Edward Feser, which can be read here (this online article is a shorter, altered version of a similar chapter in his book Scholastic Metaphysics). As that article, and many others, show, metaphysics is actually prior to and more fundamental than science, if for no other reason than that science itself rests on metaphysical assumptions which it cannot itself validate. This is all to say that metaphysical principles must be analyzed/countered metaphysically, not physically. The scientific method itself rests on the assumption (albeit implicitly, and often denied by scientists) that metaphysical causation is real; if physics ever was to “discover” or “demonstrate” that metaphysical causation is not real, physics would have succeeded in undermining itself (just think, if there were no actual causal relation between our knowledge and external reality, the scientific method would crumble, and all scientific findings would be completely meaningless).

In other words, in order for the scientific method to even work, it presupposes the metaphysical principle of causality, which includes within it the act/potency distinction. Remember from my first post about the Prime Mover argument that Aristotle came up with the act/potency principles as a way to explain change, which was a heavily debated philosophical question at his time. On one side, you had those who completely denied the existence of change. On the other side, you had those who completely denied the existence  of everything but change, who insisted that stability and consistency are illusions, that everything is constantly changing (never mind the fact that if everything is “constantly” changing, then at least one thing, namely change, is never changing, thus rendering this view self defeating). Then along came Aristotle, who argued that change is real, but it is not the only real thing. He did this by proposing the act/potency principles, that change is the actualization of a potency by something already actual.

Now, as I tried to make clear in my first post, the act/potency principles are just obviously true, despite the fact that they are ignored by most scientists/philosophers today. That change is the actualization of a potency by something already actual is just common sense. Imagine that you have a lamp in the middle of an empty room. The lamp is the only light source in the room, but right now the lamp is turned off. At the moment, the lamp is actually dark. But it has the potential to give off light, due to its essence/nature as a lamp. No one would deny this, even if they think the point is uninteresting or just semantics. Now, if you go into the room and light the lamp, the lamp’s potential to give off light has been made actual. It used to be actually dark, now it is actually light. How did it do this? Because even when it was actually dark, it had the potential to be light, and that potential has been actualized by something else already actual (namely, the actual person lighting the lamp by an actual flame, or, if it is an electrical lamp, an actual person flipping the switch which activates the actual electrical conduction system). Change is just incoherent if the act/potency principles are false; there is no other way to make sense of it. And since change is obviously a real feature of the world (although, of course, not the only real feature), it is incoherent to deny the act/potency principle. It is metaphysically established, and it cannot be uprooted by the discoveries of physical sciences, even if such discoveries, such as quantum mechanics, are seemingly strange, and raise interesting questions of interpretation. Indeed, no one is really sure as of yet how exactly to interpret many of the implications of quantum mechanics, and so, if nothing else, it is at least premature to claim that these implications “prove false” classical logic or other metaphysical principles (in truth, it is not just premature, it is also impossible).

Let’s use an example from quantum mechanics, such as the radioactive decay of an unstable atom. According to an article on (an excellent source, I know), “Radioactive decay occurs in unstable atomic nuclei – that is, ones that don’t have enough binding energy to hold the nucleus together due to an excess of either protons or neutrons.” The atom is said to “decay” when the nucleus loses particles of energy, emitting radiation in the process. Notice the language which the article makes use of: the particle “escapes from the nucleus of the parent atom…by quantum mechanical processes and is repelled further from it by electromagnetism.” Even if this language is just used as a semantic means to present the concepts of radioactive decay, it is still telling that we seem unable to make sense of phenomena–even phenomena which is apparently supposed to undermine causation–without inherently causal terminology. Remember in my first post the example of leaves changing color in fall. This is obviously on a much larger scale than an individual atom, but similar aspects are at play. The leaves of the tree change color due to lack of sunlight and colder temps, which cause the leaves to cease their production of chlorophyll. The lack of sunlight is “actual,” which causes the potential for losing chlorophyll to also become actual. In a similar way, we can think of the “lack of binding energy” as an actual cause, which actualizes the potential for radioactive decay, and the electromagnetic force as another actual cause, which actualizes the potential for particles to be repelled from the nucleus. And so on.

If this is the case, what is it exactly about radioactive decay and other quantum events which lead people to claim that such discoveries demonstrate that the act/potency premises are false? It is that such quantum events are “probabilistic,” rather than deterministic. That is, there is no deterministic way to predict when the unstable atom will decay. It seems to happen “randomly” or “spontaneously,” without any external factors determining the event. But even this is not a challenge to the act/potency premises.

Think again of my lamp example. When the lamp is dark, it has the potential to be light. Why does it have this potential? It has it by virtue of being what it is, namely a lamp. Because it has its specific form/essence/nature, which includes all its relevant features, such as say an electrical conduction system, it has the ability to be either light or dark. If it did not have the form/essence/nature that it does, it would not have these potentials. After all, if I were to attempt to take a flame and light water on fire, I would not be very successful. Because the nature of water (on its own, under normal circumstances) just does not have the potential to catch fire and give off light. Thus the potencies an object has are due to its nature.

The same is true for atoms, and electrons, and protons, and all other material objects, including all subatomic particles. An unstable atom, due to its form/essence/nature as an unstable atom, has the potential to decay. If it did not have this potential, it would never decay. Now, for most modern scientists and philosophers, the notion of causation consists only of efficient causation, or the “agent” which actually does the causing. So when I swing a baseball bat, my arm swinging the bat is the efficient cause. For Aristotle, Aquinas, and the scholastic philosophers, however, there are four types of causes: 1) Material Cause, 2) Formal Cause, 3) Efficient Cause, and 4) Final Cause. To go into much depth on all four of these and their implications would require much more space in an already over length article, so suffice it to say that any four of these causes could be that which actualizes a potency, and indeed most often they all work together to do so. Now, an unstable atom, due to its essence (or its formal cause), is directed towards, or tends towards decaying (which is its final cause), as an outflow of its very nature. Its nature just is to decay at some probabilistic point in time, and so its nature can be said to be the “cause” of its decay. The fact that such decay happens at a random, “spontaneous” point in time does not mean that it happens uncaused, its cause may just not be a deterministic one. It’s formal and final causes actualize its potencies to decay. Now matter, on its own, has the potential to be instantiated with any form. So an unstable atom is an object whose potential to exist as an unstable atom must have been actualized. And thus our essentially ordered causal series continues, taking us right back to the being of Pure Act, whom we have already determined is God.

Now, I realize this argument may take some time and thought to fully sink in. It certainly did so for me. After all, on an extremely simplistic level, the argument essentially claims that if change exists, God must exist. It’s a foreign and strange idea. Things change all the time, we see and experience change everyday. Is it really possible that all such change must trace back to God? But when all of the deeper, metaphysical principles are laid out, it becomes clear that this ancient argument not only makes sense, its actually an absolute proof for the existence of God. Now it doesn’t establish other aspects about God, such as that God is a trinity, or that God has ever acted in history, etc. But there are other arguments for those other issues. What matters is that there is indeed at least one argument that takes us, by pure reason alone, to the existence of God. Two of the greatest philosophers in the history of the world, Aristotle and Aquinas, both agreed.

I know this article is already much too long, and many may find it boring and repetitive. But I take the time and care to delve into and explain such metaphysical matters because this argument, and these ideas, have much significance for me personally. The argument from motion was one of the final nails in the coffin of my unbelief; it really convinced me, in a time of confusion and despair, that at bottom there is something Real, and something knowably so. And so it is fitting to end this series of posts on the article with a lengthy quote from one of my favorite writers, G. K. Chesterton, from his book on Aquinas. Chesterton was one of the greatest thinkers of the last century, and he had, according to one writer, a “preponderance of image over linear argument” (Steven Shroeder, from the Introduction of the Barnes & Noble Library of Essential Reading version of Chesterton’s Heretics). I have presented the Prime Mover argument basically as a linear, logical argument. But Chesterton had a way with words; he knew how to strike an idea not just into the mind, but deeper, into the heart. Here is how we described the argument from motion:

“…Aquinas has confirmed that our first sense of fact is a fact; and he cannot go back on it without falsehood. But when we come to look at the fact or facts, as we know them, we observe that they have a rather queer character; which has made many moderns grow strangely and restlessly sceptical about them. For instance, they are largely in a state of change, from being one thing to being another; or their qualities are relative to other things; or they appear to move incessantly; or they appear to vanish entirely. At this point, as I say, many sages lose hold of the first principle of reality [that something exists], which they would concede at first; and fall back on saying that there is nothing except change; or nothing except comparison; or nothing except flux; or in effect that there is nothing at all. Aquinas turns the whole argument the other way, keeping in line with his first realisation of reality. There is no doubt about the being of being, even if it does sometimes look like becoming; that is because what we see is not the fullness of being; or (to continue a sort of colloquial slang) we never see being being as much as it can. Ice is melted into cold water and cold water is heated into hot water; it cannot be all three at once. But this does not make water unreal or even relative; it only means that its being is limited to being one thing at a time. But the fullness of being is everything that it can be; and without it the lesser or approximate forms of being cannot be explained as anything; unless they are explained away as nothing…” (Chesterton, Saint Thomas Aquinas).

In other words, real things change because they are not the most real thing. The branches sway in the wind, but they must all trace their way back down to the one, ancient, immovable trunk, ever standing amidst the fray, ever rooted in the solid ground, solid, unshakeable, unmovable but not at rest. For it is the trunk which holds up the branches, which sustains them; and it is God in whom are rooted all things, the entire cosmos. It is God who sustains all things in being, it is God who is the fullness of all being, who is being itself.

(This is hopefully my final post on the Prime Mover argument. The Prime Mover argument is the First of Aquinas’s famous Five Ways. I plan to do a similar series of posts on each of the Five Ways. Until then, please offer comments and suggestions below!)




As with the last two posts, I must again 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.

I would also like to acknowledge this post at Rocket Philosophy blog:

For more information about the relation between quantum mechanics and metaphysics, here is a post on Feser’s blog:

In particular, here are the sources which were quoted in the article above, in the order in which the quotations appear:

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

“What is Radioactivity?” n.p. n.d. Web. 19 May 2016.<;.

Schroeder, Steven. Introduction. Heretics. By G. K. Chesterton. 1905. New York: Barnes & Noble, 2007. Print.

Chesterton, G. K. Saint Thomas Aquinas. 1933. New York: Image Books, 2014. Print.





31 thoughts on “Prime Mover Part 3: Final Objections

  1. Mr. Jennings,
    I still have trouble conceptualizing the situation with the First Mover (FM). (By the way, even though Feser continually refers to the FM as “He,” I don’t understand why, so I refer to the FM as “it.”) I get that logically the FM must exist and that it must be able to cause movement or change in the material world even if we humans are unable to fathom how it accomplishes this. If I understand the arguments correctly, Feser / Aquinas deduces the existence of a FM, and then deduces that it has certain properties including the ability to cause change in the material world. Then we learn that the FM need not itself move or be moved because it is outside space and time. Further, some of the FM’s attributes are held only in an “analogical sense.” This is all not just abstract, but vague to me. Maybe it would make more sense to me if I understood Latin. Again, I can find nothing wrong with the logic. That’s not surprising, since I am not a logician and the Roman Church has had centuries to perfect the arguments. Nevertheless, I am uncomfortable with the result, and I can’t help thinking that there must be a flaw somewhere, if not in the logic, then in the definitions. I occasionally search the internet for some good counter-arguments and so far have had no luck. I will continue to study this. I would be grateful to you if you can point me toward some other sources that can help a layman get a better handle on this.

    Liked by 1 person

    • Hi!

      Thanks again for reading and commenting. I believe Feser refers to the PM as “he” rather than “it” because he tries to establish that the PM must be “personal” in the sense of having an intellect and will. Using the pronoun “he” just emphasizes the personal nature. Also, Feser believe the PM to be the Judeo-Christian God, which traditionally has also been ascribed the pronoun “he.”

      You seem to understand the argument itself very well. The argument does attempt to deduce the existence of a PM based on the motion we perceive around us. As I said, the argument originally wasn’t created as a way to try to “prove” the existence of God; rather, Aristotle was just trying to explain motion, and it just so happened that in order to explain motion, he had to posit the existence of a being with many of the same attributes which the normal conception of God has. I fully admit that this explanation of how some attributes are “analogical,” is indeed vague. I will try to do some more research on how exactly that works.

      If I might ask, what exactly about the conclusion of the argument is uncomfortable? I might be able to help explain a bit better. I am a beginning philosophy student, so I’m new to a lot of this as well. In writing this article, I also tried to research and respond to all of the objections I could find. For me, the most potent objections are those concerning quantum mechanics. I am trying to do a lot more research in this area, and in the future I hope to write another post going more in depth as to how quantum mechanics might pose a problem. I think one of the issues is that, as Feser noted in The Last Superstition, most modern people have moved away from the scholastic metaphysical approach which this argument is based on. Most philosophers today (that I know of) don’t really approach this argument at all, either to defend or refute it. It’s just gone out of the mainstream. For me, then, the hardest part is not the argument itself, but establishing the underlying metaphysical principles. These principles are what are most heavily debated today.

      With that being said, I too am still looking around for many resources to help understand this argument. If you haven’t already, Feser has another book entitled “Aquinas” which goes into some depth on this argument, as well as the other four arguments which Aquinas gave for the existence of God. At the back of this book is also a list of “further reading” which offers more sources. Feser’s book “Scholastic Metaphysics” is much more scholarly and dense, and it doesn’t mention this argument specifically, but it does explain the underlying metaphysics in more depth. Feser also has an online blog here:
      He writes a large amount very often, and if you use the search bar I believe he has several posts on this argument and related matters.

      I haven’t been able to find very many other resources yet that are as thorough as Feser. Here are some other blogs that I have found:

      Also, here is a blog I’ve just recently discovered on Thomistic philosophy:
      I haven’t found an article specifically on the PM argument yet, but I’ll be looking.

      If I happen to find any other good sources, I’ll be sure to let you know! Until then, if you could help me understand your difficulty exactly with the result of the argument, I will try to answer in any way I can.



  2. After much study, I have some questions and objections.
    First is how I understand Aquinas’ arguments about the Unmoved Mover, as explained by Edward Feser in The Last Superstition.
    Second are my questions & objections.

    Aquinas’ arguments for an “unmoved mover.”
    1. Aquinas deduces the existence of a First Mover (FM), because
    a. Some things move.
    b. Something must move them.
    c. There cannot be an infinite regress of movers.
    d. Therefore, there is a FM, whose existence does not need to be actualized by anything else.
    2. A First Mover must be itself unmoved, unchanging, and unmovable.
    a. If it was moving or changing, i.e., going from potential to actual, something outside it would have to be moving it. Then it would not be the first mover.
    b. It must also be unmovable to avoid an infinite regress of movers. So the FM must be fully actualized, with no potential. Having no potentiality, it could not possibly move or change.
    3. There can be only one FM.
    a. If there were more than one being of pure actuality, there would have to be some way to distinguish between them; one would have to have some feature the other one lacked.
    b. To lack a feature is to have an unrealized potentiality.[1]
    c. A purely actual being has no unrealized potentialities, by definition.
    4. An FM must be non-material.
    “To be a material thing entails being changeable in various ways.” An FM is unchangeable, so it must be non-material.
    5. An FM must be eternal.
    a. Beginning or ceasing to exist would be an instance of change.
    b. An FM cannot change.
    c. It must be outside time and space.
    6. As “the common first member of all the various essentially ordered causal series that result in these instances of change, the Unmoved Mover is outside and distinct from them all, as that which sustains the entire world in motion from instant to instant.”
    7. An FM must be omnipotent, omniscient, and omnibenevolent.
    Feser (p. 96) says that a first mover must be itself unnmoved or unchanging, and unmovable, lacking any potential, and thus is pure actuality. On the next page he says “…to lack a feature is just to have an unrealized potentiality [see 3b above], and a purely actual being, by definition, has no unrealized potentialities.” He says this to explain why there cannot be more than one purely actual being. Two such could not be distinguished from each other unless one had something the other lacked, and that is not possible.
    Why is that not possible? Because,
    “… the Unmoved Mover, as the source of all[2] change, is the source of things coming to have the attributes they have. Hence He[3] has these attributes eminently if not formally. That includes every power, so that He is all-powerful.”[4] (p. 98)
    [1] Why? I lack the ability to bring my dead mother back to life. Does that mean I have an unrealized potential to do that? That makes no sense to me.
    [2] “All” includes the non-material world as well as the material world. How does he know this?
    [3] Where does Feser get “He”? If God is “Being Itself,” as he notes on 109-110, to me that is too abstract and vague to say that God is also sexual. But if you insist (as he does elsewhere) that God is the source of all attributes, that would include sexuality all right, but then that must also include femininity as well as masculinity, so “He” would not be appropriate.
    [4] If the FM is unmovable, then it lacks the power to move and is not omnipotent.
    If it has the power to move and does not do so, then it is not fully actual.

    Paul Buchman


    • Hi again, thanks for leaving your questions/responses, your comments have helped me think through these things better as well. As far as your presentation of Aquinas’s argument, I think you’ve got the gist of it down. Later this week (probably Friday) I’ll be posting a condensed, outlined version of the argument for people who don’t want to read through all three articles.
      Now the questions:
      1. When Feser says “to lack a feature is to have an unrealized potential,” his phrasing is a bit awkward. What he means by “feature” here is just an actualized potentiality. If someone, for example, has brown hair, that is a physical feature of their body. However, a person with brown hair lacks the feature of blonde or black hair; but they still have the potential to have blonde or black hair, it’s just an unrealized/unactualized potential. To use another example, a tree lacks the ability to speak english, but that doesn’t mean it has an unrealized potential to speak english. Trees don’t have the potential to speak at all. So lacking a feature isn’t necessarily synonymous with having an unrealized potential. If a feature is an actualized potential, then things which lack features might have an unrealized potential to do something, or they just might not have that potential at all. You do not have the feature of being able to bring your mother back to life, meaning you don’t even have an unrealized potential to do so.

      2. The principles that motion is the actualization of potencies, and that such actualization of potencies requires another being already in act to actualize it, are metaphysical principles, not physical laws. This means that they apply to everything that exists, whether material or immaterial. When immaterial things move, this is still potency being actualized, and still requires an actualizer. As such, all immaterial beings that might exist still depend upon the prime mover. We’ve just never directly experienced any immaterial beings, so it’s hard for us to conceptualize/imagine it. But the metaphysical principles still apply

      3. Feser has several reasons why he refers to God as “he,” but none of them are really central/essential to the argument. That’s why I tried for much of my articles to just refer to it as the “being of Pure Act,” to avoid any possible confusion. As I said in the articles, the prime mover argument just takes us to a being of Pure Act, it doesn’t take us any further. But Feser has separate, independent reasons for believing that Christianity in general is true, and thus that the being of Pure Act has revealed itself to humanity as Yahweh, or the God of Israel, or Jesus, etc. Because Feser believes on separate grounds that Christianity is true, then he believes that the being of Pure Act is this God of Christianity. And the Judeo-Christian tradition has for thousands of years identified this God as “He.” So using that pronoun is just a way of staying in line with that tradition.
      Another reason is that Feser believes, and I have tried to show, that there are possible reasons for thinking that the being of Pure Act is “personal.” This just means that the being of Pure Act has intellect and will. So to separate the being of Pure Act from a purely inanimate object or impersonal force, Feser employs a personal pronoun. This is not meant at all to say that God somehow has a gender or sexuality. Gender and sexuality are obviously traits of our physical biology, and no theologian (except maybe within the Mormon tradition) would say that God has a body with physical, biological traits. In that sense, of course God is not a “he” or a “she.” But God is still, according to the argument, personal, and those are the pronouns we use to denote personhood.
      In all truthfulness, the pronoun used really is not central/essential whatsoever at all to the argument. You could call the being of Pure Act pretty much anything. I really wouldn’t get too caught up on this point.

      4. Here’s your next objection:

      “If the FM is unmovable, then it lacks the power to move and is not omnipotent.
      If it has the power to move and does not do so, then it is not fully actual.”

      I’m not sure why this would be the case. The prime mover argument is dependent upon these metaphysical claims: that some things move and that things that move must be moved by something else. But we have to be careful with the term “move” because there are different senses in which it can be used. If I “move” my arm, the arm is what is actually undergoing motion. Relative to my arm, the best of my body is not actually “moving,” even if the rest of my body is what enacts/causes the motion of my arm. It IS a metaphysical principle that whatever is moved, is moved by another. It is NOT a metaphysical principle that whatever moves something else, must itself be moved.
      As I’ve said before, the difficulty is that we only experience material things moving. Whenever something material moves, it is moved by something else which is itself moving. Why is this? Because everything material has potencies, and potencies are limiting. Let’s say that right now my hand is at rest. But suddenly I move it. When my hand was at rest, my arm was also at rest. In order to actualize the potential for my hand to move, my arm also has move. That’s why the essentially ordered series exists. Anything with potencies, in order to move something else, must have its own potencies actualized. But a being of Pure Act has no potencies; it is able to actualize the potencies of other objects with having potencies in itself be actualized. The FM is unmovable in the sense that it cannot undergo motion/change within itself; but it can still “move” as in moving other objects. I know this is again hard to conceptualize since we have no direct experience of such a being, but I’ll reiterate the analogy of moons and a sun. Moons, by their very nature, do not give off light. They can only reflect light from another source. So imagine we have a chains of moons, and each moon reflects the light from another moon, and so on. If this were the case, we would never have experienced anything like a sun which is capable of giving off its own light without reflecting the light from something else. And yet we’d know, by reason, that such a sun must NECESSARILY exist, because the moons all must have a source for their light. In our experience, we only know objects which move by “reflecting” the motion of something else; and yet we know that a being must exist which does not reflect motion from something else, which is the source of all motion. This being would cause all motion in other beings, without itself being moved.

      I hope this helps in some way. If you have further questions/responses to the argument in general or what I just wrote, feel free to leave them at any time.


  3. Harrison, Thank you for responding to my questions. I want to post my one-line comments your response, then I have one more question, and that will bring me up to date.

    >You do not have the feature of being able to bring your mother back to life, meaning you don’t even have an unrealized potential to do so.
    That’s what I thought, too. I will come back to this later.

    >We’ve just never directly experienced any immaterial beings, so it’s hard for us to conceptualize/imagine it. But the metaphysical principles still apply
    OK. I can accept that for now.

    >the pronoun used really is not central/essential whatsoever at all to the argument.
    I knew that. I should have made this comment separately.

    >we know that a being must exist which does not reflect motion from something else, which is the source of all motion. This being would cause all motion in other beings, without itself being moved.
    Yes, we know this because it is deducible from the premises.
    >I hope this helps in some way. If you have further questions/responses to the argument in general or what I just wrote, feel free to leave them at any time.
    Thank you, Harrison.
    “… the Unmoved Mover, as the source of all change, is the source of things coming to have the attributes they have. Hence He has these attributes eminently if not formally. That includes every power, so that He is all-powerful.” — The Last Superstition, 98

    Why must an Unmoved Mover be omnipotent?
    1.) We don’t know everything about the non-material world or about non-material beings. We only know the material world for certain. Even though Aquinas and others may have deduced the existence and some of the properties of a non-material world and of an Unmoved Mover, there are still aspects of the non-material world of which we are ignorant. This can be demonstrated by asking how a non-material Unmoved Mover effects change in the material world.
    2.) Since we don’t know everything about the non-material world, isn’t it possible that the Unmoved Mover lacks the power to do something as part of its nature, thus allowing it to be fully actualized yet not omnipotent?
    As we discussed about one of my previous questions, the power to do something, say, to travel at the speed of light under my own power, does not imply that I have an unrealized potential to that. Might this not apply to our Unmoved Mover as well?



  4. Under #2 in previous post
    I should have written
    “the fact that I do not have the power to do something, say, to travel at the speed of light….”


    • That’s an interesting point. “Omnipotent” is just one of the attributes that’s normally applied to the God of classical theism, but, in all honesty, the term is a bit vague, and recently some philosophers have suggested that the attribute might actually be incoherent. You may be familiar with the humorous, paradox type questions such as “If God is all powerful, can he create a stone so heavy that even he can’t lift it?” I remember I had a teacher ask that question to my class when I was in sixth grade, and I drove myself crazy for several weeks trying to come up with an answer. But, in fact, a lot of theologians and philosophers have no trouble at all answering such questions with a firm “no.” Many philosophers/theologians, including, popularly, C. S. Lewis, have insisted that “omnipotence” does not entail the ability to do logically contradictory/incoherent things. So God cannot create a square circle, or create an unmarried bachelor, etc, because these things are just not even logically possible. So the point of saying all that was just to explain that even amongst philosophers, there doesn’t seem to be a really settled, definitive conception of all that “omnipotence” entails. In popular usage, it normally means something like “all powerful relative to the physical universe.” So when many people say “God is omnipotent,” what they mean is just that God created/brought into existence the physical universe, that he controls and sustains it, etc.
      When it comes to the Prime Mover argument, however, it might mean something a little different. You’re right that we don’t know everything (or even very much at all) about the immaterial world, only what we can deduce from these arguments, or perhaps (if christianity is true) what God has revealed to us about it. We know from the argument that a being of Pure Act is ultimately the source/cause of all motion that exists. So anytime anything changes or moves, the being of Pure Act is the source/cause. Meaning that the being of Pure Act must have the “power” to cause/sustain literally EVERYTHING that moves/changes. This includes things beginning to exist, including the entire universe. Especially when coupled with Aquinas’s Second Way, which I’m currently writing about, these arguments reveal a being which ultimately causes just about everything that happens. That must require an overwhelming, inconceivable amount of “power”. Furthermore, I really like the example of moons. In the example I gave, I imagined that there’s a planet somewhere that can’t see any star, but is entirely lighted by an extremely bright moon. This moon, in turn, didn’t reflect the light of a star, but of another moon. When you actually think of the science behind this, in order for one moon to be able to reflect the light of ANOTHER moon, that second moon must be proportionately much larger and much brighter. And if that second moon were actually just reflecting the light from a third moon, that third moon, again, would have to be exceedingly larger and brighter. In effect, the second moon would have to be about as bright as our sun is, so think about how bright the THIRD moon would have to be, and so on. It’s the same with motion. If a stick is moved, the arm has to have more power to move than the stick. Each step back in the series would have to have inherently more power. So imagine how much power the being of Pure Act would have at the end of the series.
      But your question was, even if we know the being of Pure Act is the ultimate cause of everything that happens in the physical world, couldn’t there be some power that he doesn’t have, relative to the immaterial world? Again, that’s a really interesting question, but I’m not sure it’s one that’s able to be answered. That’s why I try to limit my use of terms like “omnipotent.” Omnipotent, when literally defined, would mean the power to do absolutely ANYTHING. But we’ve already seen that there are some things which God just can’t do, such as create a square circle. Another way we might think of it, instead of thinking of it in terms of omnipotence, is that God is the MOST powerful being out all beings that exist. Even if that doesn’t entail the ability to do literally everything, it does entail being the source and cause of the existence of every other being; so there could not possibly be a being more powerful.

      Again, this is a really interesting topic, and I may write a full length article about it at some point. Thanks for asking.


  5. I feel like the First Way only proves that there is a First Mover that is first in the sense of having purely actual causal efficacy relevant to a per se causal chain. It doesn’t show that the First Mover is pure act, devoid of all potencies. It may as well have certain potencies that aren’t relevant to its role as First Mover in a causal series that is ordered per se. Do you mind explaining this? I think it requires further argumentation.


    • That’s an excellent question that I never touched on in this series. I think there are a number of responses.
      1) The first and most immediate answer is to perhaps agree, but then contend that the First Way doesn’t necessarily require that the First Mover be *absolutely* Pure Act with *absolutely* no potencies. Sure, the argument perhaps would fail in its original intentions to prove a being of Pure Act, but I think even so it would not fail to prove the existence of a “God” like Being anyways. For even if the First Mover were not absolutely Pure Act, its actuality would still need to be such that all moving, changing things in existence (which amounts to pretty much the whole universe) would be caused by it. So we are left with a super-powerful Being which causes the activity of all things in the universe. At the very least, this poses significant problems for naturalism.
      2) But I don’t think the argument fails to prove the existence of a Being of absolute Pure Act. Ed Feser gives this response in his book “Aquinas”. The First Way starts from the movements/operations/activities of things and seeks to explain them via their causal chain, arriving at an ultimate causal explanation. But at some point in the chain, the causes must transition from being just causes of operation/activity to being causes of existence. I briefly noted this in one of my posts, that even to just exist in time is a type of motion, since a finite, temporal thing’s potential to exist must be continually actualized from moment to moment. As the Third Way tries to show, even “necessary” beings that are not absolutely Pure Act must have their potency for existence actualized. And it seems like the only thing that does *not* need its potency for existence actualized would be a Being of *absolute* Pure Act. Because in any other thing, if it has any potencies whatsoever at all (even potencies that aren’t relevant to the causal chain), it will be a metaphysically composite being, and any composite being must have a cause of its composition. So if the First Way establishes a First Mover who is pure act in respect of the causal chain but not pure act in itself, then it itself will just need some further, more prior being to actualize its own existence, and this more prior being will be the real Being of Pure Act.
      These are just my initial thoughts on the matter. There’s probably much more to it, but I’d have to spend some more time considering.


      • Thank you for the reply. Great information here. Could you elaborate a bit more on your understanding of a “metaphysically composite being” and why it requires a member prior to itself?


        • Sure. Composite beings in general are just wholes that are made up of parts. There can be what we might call “physical” composites which Aquinas refers to just as “bodies”; these are the normal objects of our experience that are made up of distinct, interacting material parts. But then there are what we might call “metaphysical” composites which may or may not be physical in nature, but are nonetheless composed of distinct, interacting parts or “principles”. Aquinas holds that all physical things are composites of matter and form, for instance. It is composite because neither the form by itself nor the matter by itself are equivalent to the whole of the thing; and at the same time the whole cannot exist without the parts. Because of this Aquinas argues that “every composite is posterior to its component parts, and is dependent on them; but God is the first being” (ST I, Q.3, Art.7). In other words, if the whole is dependent upon the parts, then the parts must be in some sense prior to the whole. If the whole cannot exist without the parts, then something other than the whole itself must have caused/arranged the parts. So if the First Mover is not absolutely simple (non-composite), then there must be some prior being which has caused the First Mover to exist, and that prior being would be the actual first mover. Act and potentiality are metaphysical “composites” or parts, and a being that contains both act and potency would not be absolutely simple. So the First Mover cannot be composite of act and potency, and hence must be Pure Act.


      • Thank you! I’m a novice to Thomism, so I’m not well-acquainted with certain concepts. Is there a particular book, article (perhaps something by Feser) that goes further into the notion of composition?


      • You’ve cleared up some of my concerns. I’m curious, though, why does having potentials (even ones that would be irrelevant to a per se causal chain in this case) necessarily mean that a being has a union of parts?


        • The term “parts” should here be understood in a broad, metaphysical sense as meaning just distinct aspects of a thing that considered altogether form the whole of its reality. A “mixture” in a physical sense is a nice image of what this is getting at. In physical sciences (especially chemistry), if there exists a “mixture” composed of two distinct substances that are different in nature, then there must be something that “bonds” or keeps the two substances united; i.e. there must be an explanation for why two substances that are different in themselves are interacting together in a whole. In an analogous sense, Thomists would say that “act” and “potency” are intrinsically different, and so for any being that consists of both act and potency together, there must be some prior explanation as to why. A “simple” being is a being that is all that it is and can be at once, in itself, by itself. A composite being is a being that, in order to be what it is, relies on something other than itself.


      • How does a prior member bond or unite a latter member with regards to act and potency? I’ve never pictured act and potency being “bonded.” I’ve always thought that a being which exhibits act and potency only does so because a prior member is actualizing a potency, not bonding a potency to act.


        • Well, in order for a prior member to actualize the potency of a certain object, that object must first *have* the potency to be actualized. Potencies are a part of the nature of a thing. The prime mover argument gets at the fact that the potencies of a thing have to be actualized by a first member, but at a certain level, as Feser points out, the argument will have to, to some extent, shift from just dealing with the motion of things to dealing with the existence of the things that are moving. It’s here that it becomes clear that the First Mover could only be a simple being of Pure Act.


    • I think k I was more concerned with the use of the word “bonding” to describe the actualization of a potency. I’m still trying to understand why a being composed of act and potency needs a prior member to explain said composite. It seems to me that we could have a being who is purely actual in some causal chain but still has potentials irrelevant to that causal chain. In that case we don’t need a prior member to explain its actual power with regards to a specific causal chain, and we don’t need any prior member to explain the existence of the irrelevant potentials–perhaps the potentials are just there and they may never be (or ever could be) actualized. Under this view we can still have a first mover but it just isn’t pure act.


      • I am reading Peter Coffey’s Ontology and I’m starting to come to a full appreciation of the scholastic understanding of existence as the ultimate actuality and essence as the seat and source of a being’s operations. If this is the case then a being whose existence is purely actual would just be purely actual–its essence would be pure act and would operate in a purely actual way. That is, it wouldn’t have any potentialities, even ones irrelevant to its existence in a specific per se series (be it one that involves merely its causal efficacy or one that involves its very existence). Furthermore, I’m starting to grasp the profundity of the Existential Argument which I think may get us to Existence itself. And with existence being the ultimate act, sheer Existence (essence identified with existence) would just be pure Act, no potentialities.

        Liked by 1 person

        • Sorry for the delayed response. Yes, I personally think the Existential Argument is one of Aquinas’s overall strongest and one of my personal favorites (along with the Fifth Way, perhaps). One of its current strengths is that, although traditionally, of course, it has depended upon an essentialism, contemporary scholars such as Brian Davies have attempted defenses of it without appealing to a scholastic essentialism (although I think essentialism can be defended, a lot of people today are skeptical of it). Anyways, I think seeing the First Way in light of other arguments probably does solve your question. If, however, you wanted to defend the First Way on its own, apart from other arguments, I still think this can be done. What the First Way is primarily trying to get at is a Mover that is the source of its *own* actuality, that does not derive its actuality from anything other than itself; and I think Aquinas would argue that only a being of absolutely Pure Act could possibly be the source of its own actuality. What I was trying to get at in my response was the idea that if a being has a nature that is composed of both act and potency, there must be some prior explanation for its nature being that way, and if it has a prior explanation for its nature, then it doesn’t seem it could be the source of its *own* actuality, since the source of its nature is something else. The First Mover couldn’t just be something that “has” actuality in the same way that other things “have” actuality. These other things “have” actuality insofar as they have potentials which *have been actualized* by something else. But if the First Mover “has” actuality in this sense, then it’s just not the First Mover. And if the being is the type of thing with potencies, even potencies irrelevant to its status in a causal chain, then it would seem to be the type of thing that receives its actuality from something else, not something that *just is* its actuality, which it would have to be in order to be the First Mover. It’s difficult to me to conceive of how something could just *be* actuality and still have unfulfilled potencies. This takes us close to what the Existential Argument gets at as well, since actuality and existence are equivalent in the scholastic tradition. For the First Way, I really like the analogy of suns and moons, which I used briefly in this post. The First Way is arguing that in a causal chain, every member is like a moon that has no light of its own but reflects light from some prior member. Since there must be a source to all the light, there must be a “sun” that is its own light. But it’s difficult to think of how something that *is* its own light could also even in principle “reflect” the light of something else in the way that a moon does. Light just is light, it doesn’t reflect light. This is a simplistic analogy of course but I think it is a nice illustration of what the First Way is arguing for: not just a first mover that “has a lot of actuality” but still also by its nature has potencies which could in principle (even if never in reality) be actualized; rather the First Mover has to be different in kind than all other members, something that just is actuality and is it itself the source of all actuality, which couldn’t have any potencies. Again, though, I think you’re right that seeing the First Way in light of other arguments helps.


  6. Thank you for the reply. You have been very helpful. One more thing, would you say we sorta tap into a type of PSR intuition whenever we see composites? So, for instance, all being that isn’t pure act is necessarily a composite of actuality and potentiality. When we see a being who is actualized in some respect but potential in others, we would be hesitant to conclude that that just is the case–that is, appeal to some brute fact. Rather, we seek a reason for why it appears to be actual and potential–namely, there is something outside of it actualizing a specific potency. So, when we come to the First Mover, it makes no sense to make it suddenly immune to this PSR intuition and view it as a composite which just inexplicably has actuality and potentiality without an outside being actualizing a potential among many. In other words, where there is both act and potency, there is some other being responsible for its act.


    • Yes, it definitely does get at something like a PSR, especially when considered in relation to St. Thomas’ essence-existence distinction. Before a thing exists at all, its essence is just a potential to exist. So if something exists, it is either 1) something whose essence is identical to its existence, in which case it would just *be* pure existence (or pure act), or 2) something whose essence is distinct from its existence. But if its essence is distinct from its existence, its essence must have been actualized, *given* actuality that it did not have on its own. When the essence is actualized, i.e. given an act of existence, it still has further potencies rooted in its nature. So when an egg is fertilized, the human essence has been given existence, but it still has a whole bunch of unactualized potencies, such as the potency to grow/develop. But if its essence just was existence, and hence just way actuality, it wouldn’t make sense for it to have unactualized potencies. So the fact that a thing has unactualized potencies points out to us that its essence is not its own being, and hence it is not the source of its own actuality, so we know there must be some prior cause. I’ll be interested in seeing how Feser develops his argument from composite beings in his upcoming book, it should be quite interesting

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