Change is something existing potentiality becoming an actuality. Only what is already actual can cause something to go from potentiality to actuality.
If we end up agreeing that there would have to originally be an entity that caused everything to go from potentiality to actuality, it doesn’t mean that the uncaused cause created all potentiality. The argument hinges on the relationship between things transitioning between states, but doesn’t comment on potentiality itself. Since the goal of the argument is typically to show that an entity that not just caused the events to begin but caused everything to exist, the argument would fall short.
I would guess the response to this criticism would have to posit qualities of potentialities that are beyond our experience. Since we simply have experience of things changing from potentiality to actuality, much of the proposed qualities of potential entities would be unfounded speculation.
You claim that the goal of the argument is to establish an entity that caused everything to exist. (What do you mean by “typically”? Do you mean the goal of cosmological arguments is typically to establish the cause of the existence of all things?) The goal of this argument, for Aristotle, was to determine the cause, or explanation of all motion. The goal for Aquinas (according to some Thomists) was to establish the existence of a being worthy of the name God, or god. So, it is hardly a critique to say the argument establishes the existence of a being who is the cause of all change, but does not establish that this being also created all things. After all, it would be a strange sort of atheism to grant that a supernatural being exists who causes all change.
Keep in mind, this argument claims that there must be an Unchanging Changer who is here and now ultimately causing all change to occur. It is not claiming that at some point in the past, something had to get the dominoes moving, or set the ball rolling. And it is not attempting to show that the universe was created at some time in the past. I was very explicit about this claim in the two articles. The series of changing changers, “does not necessarily stretch back in time, but it instead stretches upward and outward in hierarchy. Even if the effects take time to manifest, so that the ultimate effect is not simultaneous in time with a previous cause, the series is still simultaneous in causality.” Besides, Aristotle thought the universe existed eternally, and Aquinas thought it could not be proved either way without Divine revelation.
Potentiality by itself, apart from something actual, just has no being – it’s nothing, it doesn’t exist. Act can logically exist by itself (and the argument is an attempt to show that it does), but even logically, potentiality cannot exist by itself, since it is the potential of and for something actual. So, act is ontologically prior to potency.
(If you’re trying to imagine creation ex nihilo, don’t. I would consider that a separate discussion. For now, I’ll settle with an argument that establishes Theism, even if we still have the possibility of an eternal universe.)
Now, there are a couple of short paths to take in order to show that this cause of all motion is also creator. As one example, we could adopt Feser’s solution (see footnote 6 of the first article). We could argue that the very existence of things that could potentially exist in some other way, or not at all, must be actualized by the Unmoved Mover. This would show that even eternally existing things, if they have potential to exist differently, depend on this Being for their existing. So even if the universe is eternal, its existence is upheld by the Unmoved Mover, and in that sense He is Creator.
At the very least, whatever things began to exist, their coming into existence was a change, caused by the Unmoved Mover. The only remaining question is whether eternally existing, changeable things exist, and if can we say whether or not they are caused by this Being in some way. I would say yes, because Pure Being, or existence itself, is the cause of being in whatever has it to a lesser degree. But I won’t argue that now, because I just don’t need to argue for what might “typically” be the goal of cosmological arguments. If the argument is successful, we’ve at least established Theism, and the rest is just a development of natural Theology.
Now I have answered your objection without appealing to “qualities of potency that are beyond our experience,” but only by analyzing the very idea of it. The very concept as a solution to the Parmenidian dilemma rules out an independent ontology. Your real objection here is to question whether or not the discussion of being can be held at all. Because if we can discuss being, then potentiality really does solve a metaphysical dilemma, and really can be analyzed as some feature of the world. If we can’t, then the dilemma we face is not that of Parmenides: we must choose between skepticism or fideism. And this objection, I’d like to respond to all by itself.
At the very least, it is nothing material, nothing with dimension or extension, nothing with quantity or measure. It is nothing inert, but it is active – since it changes all things changeable. It could be nothing temporal, because it is utterly unchanging. There can be only one such being, even in principle, since as Parmenides showed us, being is only differentiated by potency. So pure being, or pure act, would be utterly one and undifferentiated.
(1) You say that the proposed entity has no quantity or measure, but then go on to talk about it as a thing separate from other things. If something has no quantity, it cannot be referred to as a thing, since that implies it could have a quantity of one.
You’ll have to forgive me on this point. I found myself getting a little poetical. All I really mean is that it’s not quantifiable, not divisible, not composed of parts, no quantifiable features such as temperature, dimension, extension, duration, mass, charge… etc.
But isn’t “one” a quantity? Well, sure, but one is also a transcendental according to Aquinas. Let’s set that aside for now.
The reference to an undifferentiated one could refer to everything in existence. This would possibly be compatible with Parmenides view of the world, but probably not the view of God Aquinas is trying to show. The view that God is a part of everything, in the sense described here, would be a kind of Pantheism.
I’m now sure how I am describing God as a part of everything. I am distinct from you, and this coffee cup, because of the potentialities in each thing. For God to be a part of everything as described by pantheism, he would share in our potentialities. As a being of pure being, He is wholly other. Both a mug and a paper Starbucks cup participate in “coffee cup,” but “coffee cup” is neither a mug, nor a paper Starbucks cup, nor both. In the same way, a Being who is being itself is not the same as you or I, if for no other reason than because you and I both participate in being.
(2) On a different note, to describe something as unchanging is to refer to its state from one moment to the next. That is, we say, for some length of time, the thing didn’t change. If the entity exists outside of time, we cannot ascribe the attribute of unchanging to it since that description assumes it existing in time.
This is muddled. Immutability is what follows from being devoid of potency. Timelessness, follows from immutability, since time “is simply the measure of before and after in [change].” [ST 1.10.1] But even if you dispute the Aristotelian notion of time, the point is, Pure Act is immutable.