I seriously doubt that Aquinas was simply using his imagination in proposing the five proofs for the existence of God. In his view, these proofs are based on metaphysical and demonstrative principles, the denial of which is incoherent.
You seem to want to suggest that an order of per se movers or efficient causes can infinitely regress. Aquinas is very clear that this is not possible. The first proof concerning motion or change and the impossibility of an infinite regress in things moved is a demonstration that stands on its own whether you consider the other proofs or not. However, all the proofs should be considered together if one wants to get a more thorough idea of Aquinas’ view of God’s causal activity in the world.
Concerning the first proof and the principle that whatever is moved is moved by another, for motion is nothing else but the reduction of something from potentiality to actuality, then as Edward Feser points out in his book Aquinas, “as should be evident, such a series can only possibly terminate in something which is not reduced to act or actualized by anything else, but which just is in act or actual, and thus unmoving.” This is the logical conclusion otherwise there would be no motion or change in the world which is contrary to our sense experience. Accordingly, Aquinas writes “the first and more manifest way is the argument from motion.”
I would also recommend reading Aquinas’ Summa Contra Gentiles, Book 1, chapter 15. Here, Aquinas goes into more details concerning the unmoved mover and the impossibility of an infinite regress. One of the arguments in this work, if I’m understanding it correctly, is that if one regresses to infinity in things moved by another all simultaneously existing, you would have one and the same thing moved in both infinite time and finite time which is impossible. For example, suppose I move a stick with my hand right now, it was not previously moving, now it is. This is a new event or motion. If the stick is moved by the hand, the hand by the arm, and so on to infinity; if you consider this infinite number of movers and things moved as one body, so to speak, this one body moves in infinite time whereas the stick moves in finite time, I just started moving it. It appears to me that if you regress to infinity in movers of the stick, I would have had to be always moving the stick for all eternity which is plainly false. We could also ask the question whether or not it is indeed possible to pass through the infinite or infinite time for an effect that is dependent on an infinite number of things all simultaneously existing. I believe I have read that Aquinas, following Aristotle, says that to pass through such an infinite is not possible.
(continued from post #94)
Actually, it is in St Thomas’ Summa Theologica, I, q.7, art.4, where St Thomas mentions the impossibility of passing through an infinite number of things that a particular thing is dependent on for its existence. This concerns an order of efficient causes per se all of which are simultaneously existing. The question is about whether an infinite multitude can exist. He writes:
“I answer that, A twofold opinion exists on this subject. Some, as Avicenna and Algazel, said that it was impossible for an actually infinite multitude to exist absolutely; but that an accidentally infinite multitude was not impossible. A multitude is said to be infinite absolutely, when an infinite multitude is necessary that something may exist. Now this is impossible; because it would entail something dependent on an infinity for its existence; and hence its generation could never come to be, because it is impossible to pass through an infinite medium.”
If we continue reading the article in question, St Thomas appears to gives us another reason for the impossibility of an infinite regress concerning an absolute infinite multitude in an order of efficient causes per se. He writes:
"A multitude is said to be accidentally infinite when its existence as such is not necessary, but accidental. This can be shown, for example, in the work of a carpenter requiring a certain absolute multitude; namely, art in the soul, the movement of the hand, and a hammer; and supposing that such things were infinitely multiplied, the carpentering work would never be finished, forasmuch as it would depend on an infinite number of causes. But the multitude of hammers, inasmuch as one may be broken and another used, is an accidental multitude; for it happens by accident that many hammers are used, and it matters little whether one or two, or many are used, or an infinite number, if the work is carried on for an infinite time. In this way they said that there can be an accidentally infinite multitude. "
In the new english translation of the ST by Fr. Thomas Gilby et al.,1963, a footnote concerning the above reads: Notice that St Thomas is perfectly prepared to allow infinite time for the work (an accidental infinite multitude), yet nevertheless complains earlier against an inherently infinite number of causes that “the job will never get finished.” ‘Never’ does not mean ‘at no time finitely distant,’ but ‘at no time even infinitely distant.’ The understanding of this point is vital to St Thomas’ numerous remarks about the impossibility of infinite regress.
An order of efficient causes per accidens concerns causes that are in the same order of things or the order of only one cause. For example, the hammers in question 7 or the generation of one man from another (cf. ST, I, q.46, art. 2). However, in an order of efficient causes per se, for example, if the generation of this man depended upon this man, and on an elementary body, and on the sun, and so on to infinity, this is impossible. The effect would never be realized.
