Proving Classical Theism? An Aristotelian Argument Examined

By | March 22, 2018


It’s been about a year since I last blogged. I plan to get back into it with more consistency. This last year my wife and I became foster parents and subsequently adoptive parents to a little girl (now 3 years old), and that coupled with a few other things has made it hard to focus on philosophical issues for long enough to work them out in detail and write up my thoughts. I will be resuming my Evaluation of Thomistic Metaphysics series, but for now I’d thought I’d take a minor detour and focus for a few posts on a recent book by Edward Feser called¬†Five Proofs of the Existence of God. In the book, Feser develops and defends five arguments drawn respectively from Aristotle, Plotinus, Augustine, Aquinas, and Leibniz. As he develops them, each argument is not just an argument for theism, but more specifically for¬†classical theism.

Classical theism must be distinguished from what we might call mere monotheism, the view that there is one, metaphysically necessary, personal God, who is essentially maximally perfect in power, knowledge, and goodness, and upon whom all other (concrete) beings are ontologically dependent. To these claims classical theism adds that God is also absolutely simple, timeless, immutable, and impassible. And as developed by luminaries such as Thomas Aquinas, classical theism includes the claims that God is Pure Act and Being Itself. This is the sort of God the existence of which Feser wants to prove.

I’m interested in his arguments because, for reasons I note in my introductory Evaluation of Thomistic Metaphysics post (link above), I believe that classical theism is metaphysically untenable and theologically disastrous for biblical Christianity. So if Feser is right that classical theism can be “proved”, then I’ve got a problem. Either my negative assessment of classical theism or my understanding of biblical Christianity or both, must be mistaken. Having looked over Feser’s book, however, I don’t believe that I am mistaken. Instead, I think that each of his “proofs” fails because each depends on one or more assumptions that can be reasonably denied. To make good on this claim, I’m going to post on each of his five arguments and explain why I think each fails to establish classical theism.

The Aristotelian “proof”

Feser’s first argument derives from Aristotle. He develops it at considerable length (pp. 35‚Äď37), breaking it down into a total of 50 (!) propositions. I’m not going to reproduce the whole argument here because it’s the first part that most matters. The rest of the argument just works out the consequences of the first few premises, deriving along the way the key theses of Thomistic classical theism.

Without further ado, here’s how the argument starts:

  1. Change is a real feature of the world.
  2. Change is the actualization of a potential.
  3. The actualization of a potential is a real feature of the world. (From 1 and 2)
  4. No potential can be actualized unless something already actual actualizes it. (The “Principle of Causality”)
  5. Any change is caused by something already actual. (From 2 and 4)
  6. The occurrence of any change C presupposes some substance S which changes.
  7. The existence of S at any given moment itself presupposes the concurrent actualization of S’s potential for existence.
  8. Any substance S has at any moment some actualizer of A of its existence. (From 5‚Äď7)
  9. A’s own existence at the moment it actualizes S itself presupposes either (a) the concurrent actualization of its own potential for existence or (b) A’s being purely actual.

From here the argument proceeds to rule out the infinite regress threatened by 9.a, concluding that there must exist a purely actual Actualizer (God) who concurrently actualizes everything else. Other classical theistic attributes are then derived.

Evaluating the argument

Despite its length, Feser’s argument isn’t developed as carefully as I would like. For example, the key concept of¬†change isn’t defined in the argument. The closest we get is premise (6), but that’s nowhere close to a definition. It only gives us a necessary condition for change (i.e., that it pertain in some way to at least one substance), not necessary and sufficient conditions. So it doesn’t clearly delineate what counts as a “change”. To help the argument along, let’s introduce the familiar distinction between¬†intrinsic and¬†extrinsic¬†change. Intrinsic change is change¬†in a thing, and therefore presupposes the persistence of the thing through the change and, arguably, the actualization of an intrinsic potency of the thing to change in that way. To borrow an example from Aquinas’s First Way, a log placed near a fire will get warmer. The fire, which is actually hot, actualizes the log’s intrinsic potency to become hot. Extrinsic change, in contrast, isn’t¬†in the thing that is said to change. It consists either in (a) an intrinsic change in something else, or (b) in a changing relation between things. As an example of (a),¬†when I start thinking about my wife she might be said to acquire the property¬†being thought about by me, but obviously this need not make any difference in or¬†to her, especially if she’s far away and doesn’t even know that I’m thinking of her. An example of (b) might be two distantly related particles moving away from each other in empty space. The relation (the distance) between them is changing.¬†We might think of this as a change¬†in¬†the two-particle system, but¬†it doesn’t involve a change in either of the particles considered each on their own.

It is undeniable that change of both sorts, intrinsic and extrinsic, is a real feature of the world (premise 1). It’s also clear that¬†intrinsic change involves the actualization of a potential (premise 2). It’s not so clear, however, that extrinsic change involves the actualization of a potential, or at least that it involves the actualization of the sort of potential that needs an actualizer as per premise (4). Consider the hypothetical two-particle system again. Assume that both particles are moving away from each other at uniform speed with no forces acting upon them. According to Newtonian mechanics, each particle is in a uniform¬†state of motion and its continuing in that state of motion doesn’t need to be explained (at least as far as physics goes). What would need to be explained is if one of the particles slowed down, sped up, or changed direction. For that we would have to posit something exerting a¬†force upon the particle. The force would actualize the particle’s intrinsic potential to accelerate or decelerate.

So it’s not clear to me that the so-called “principle of causality”¬†is true as stated because it’s not clear to me that what sorts of things count as actualizations of a potential. When limited to intrinsic changes I am strongly inclined to endorse the principle. Changes in a thing (substance) need to be explained.¬†But when it comes to¬†merely relational changes, such as in the two-particle system I’ve described, I’m not inclined to think of the “potential” of each particle to be elsewhere as something that requires anything else that is “already actual” to actualize it. I would rather say that each particle¬†itself, given its intrinsic momentum, has all that it needs to actualize that potency. If (4) and (5) are understood as restricted to¬†intrinsic potencies and¬†intrinsic changes, then I can accept them; otherwise I think the claims are false, or at least such that there is no rationally compelling reason to think they are true.

We now come to (7), which is the main lynchpin of the Aristotelian “proof”. Its position in the argument seems like an abrupt change of topic. Premises (1‚Äď6) have to do with¬†change, but existence-at-a-moment isn’t a change of any sort, intrinsic or otherwise. So what’s the connection? In his informal discussion of the argument (pp. 17‚Äď29), Feser contrasts heirarchical and¬†linear series of dependency. The types of causal chains we’re most familiar with (e.g., one domino knocking over another) are linear. These plausibly involve the actualization of a potential by something already actual. But Feser wants us to focus on heirarchical cases like a cup’s being supported by a table being supported by a floor, etc. And he wants us to think of heirarchical dependency as involving the actualization of a potential (e.g., the table actualizes the cup’s potential to be 3 feet off the floor). He then wants us to think of a thing’s existence-at-a-time as involving the actualization of a potential. It is this way of thinking that ultimately requires us to posit a unique¬†purely actual actualizer of everything else, namely, a classically theistic God.

But this whole heirarchical application of act and potency and the “principle of causality” strikes me as inadequately motivated. The plausibility of the principle of causality stems primarily from cases that involve¬†intrinsic change and therefore the actualization of an¬†intrinsic potential.¬†Applying the principle to heirarchical series extends the principle far beyond the types of cases for which it seems chiefly applicable.¬†Being 3 feet off the ground is a strictly¬†relational state of the cup that doesn’t correspond to any¬†intrinsic¬†potential of the cup, such as its potential to be moved. Intrinsically a cup on a table is no different than a cup on the ground. To be sure, the table’s supporting the cup¬†explains the cup’s remaining 3 feet off the ground rather than its falling in accordance with the gravitational forces acting upon it, but it seems counterintuitive to think of this explanation as involving the actualization of a potential, mainly because it doesn’t involve a change.

I find it even odder to think of S’s existence-at-a-moment as involving an actualization of S’s “potential for existence”. If S exists at a given moment, then its existence is fully¬†actual¬†at that moment. S’s potency to exist (whatever that is) can’t exist unactualized since non-existent things have no potency whatsoever. If the question is how did S¬†come to exist, then it seems plausible to think of this as the actualization of a potential. Not a potential in S, to be sure, but a potential in something else, perhaps a potential in God to create S. And if the question is why does S¬†continue to exist in the next moment, then we might posit S’s having an intrinsic potency to exist in the next moment (perhaps a kind of existential inertia). But this doesn’t seem to be the kind of “potency” that needs to be actualized by something else that is “already actual” (if S is intrinsically unstable, however, then it might need something else to hold it together) for the same reason that our uniformly moving particles (arguably) don’t need anything other than their own intrinsic momentum to explain their being elsewhere in the next moment. But when the question is why S¬†exists at this moment, I see no compelling reason to think of this as the actualization of S’s potential for existence. Indeed, there doesn’t seem to be the actual-ization of anything because there’s no change here.¬†There’s just a¬†state of being.

I conclude, then, that (7) is, if not false, then at the very least inadequately motivated. In his informal discussion leading up the argument, Feser does little more than just insist that we think of existence-at-a-moment as involving the actualization of a potential and that we apply the “principle of causality” to this sort of actualization. If those steps be granted, then the argument for a purely actual, unmoved mover, classically theistic sort of God is, I think, hard to resist (though I find Feser’s derivations of some of the divine attributes unconvincing). But I’m not tempted in the least to grant those steps. And since Feser is the one who is purporting to offer a “proof” of classical theism, it’s incumbent upon him to defend and motivate the relevant principles. (Later on in the book, on p. 233, he argues against the idea of “existential inertia”, but he does so in question-begging fashion by appealing to the various “proofs” he offers as evidence of that idea’s falsity, when those proofs in turn presuppose the falsity of that idea. He then attempts to shift the burden of proof, as though he wasn’t the one purporting to offer a proof in the first place.)

5 thoughts on “Proving Classical Theism? An Aristotelian Argument Examined

  1. Jeff


    Thanks for the article! It raises a question in my mind. Am I wrong in interpreting the combination of (2) & (7) to be the source of the belief in creatio continua (and, hence, occasionalism?) If not, it seems to me that classical theism could tend toward the denial of human freedom. Because occasionalism seems to require that all attributes of creatures are totally caused by God.

    The only way out would seem to be to make sense of the non-correlativity of being and attribute. And I haven’t managed to make sense of that.

  2. DS

    Hi Alan, thanks so much for your review of Feser’s book. I’m currently making my way through it and I too have found a good number of Feser’s moves to be eyebrow-raising, to say the least. You seem lo be a very thoughtful, scholarly, and careful thinker, who is eager to get at the truth, even if this means going against the tide, emotional commitments, and abandoning previously held cherished ideas. I mean no offense when I say this, but given your healthy skepticism surrounding Feser’s (and others’) ‘proofs’ of God, I’m surprised that you’re not an atheist/naturalist or at least an agnostic ūüėČ

    In any case, looking forward to reading more of your illuminating posts!

    1. Alan Rhoda Post author

      I appreciate the comment, DS. Thank you.

      As to why I’m not an atheist/agnostic, I think there are plenty of good reasons to believe in God. I find some versions of the cosmological and design arguments (particularly the Kalam argument and considerations of cosmic fine-tuning / intelligent design) very compelling. I wouldn’t describe those as “proofs” of God’s existence, but in their best formulations I think they suffice to render theism much more likely than its denial. Conversely, I think the strongest atheist arguments (i.e., the various versions of the problem of evil) are compelling against versions of theism (e.g., so-called “classical” theism, or high-Medieval orthodoxy) that make God ultimately and wholly responsible for literally everything, but lose much (though not all) of their punch versus some versions of “free-will” theism (e.g., open theism), especially when coupled with epistemic modesty concerning what we should or should not expect God to do or to have done about evil. There is, of course, much more to be said pro et contra. ūüôā

      PS. I hope to continue my examination of Feser’s Thomism soon.

  3. DS

    Thanks so much for the reply and explanation! For what it’s worth, I don’t find the Kalam argument persuasive, especially Craig’s argument that an infinite regress of causes is impossible. The first premise is also not accurate- at least if it’s one that is based on our experience. Things never really ‘being to exist’ from nothing. What we call ‘beginnings’ of things are always transformations of pre-existing materials (matter/energy). But I don’t think Craig would want to accept that our universe was created out of ‘pre-existing materials’!

    I also don’t find the fine-tuning argument that persuasive. Indeed, given that we exist, it should not be surprising at all that we find ourselves in a universe where the conditions are compatible with our existence. On the contrary, what would be miraculous (and thus potentially supportive of supernatural design) is if we discovered that we lived in a universe (or on a planet, like Venus) where the conditions were incompatible with our existence!

    For a full defense of this argument, please see Ikeda and Jefferys paper:


    In any case, I look forward to reading more of your excellent and insightful analyses!


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