Aquinas on Infinite Regress

Our tendency is to think of infinite regress in a purely temporal way: an endless series stretching back in time, without end.

In his First Way (the Argument from Motion), Aquinas argues that we cannot go on indefinitely looking for a cause for things that are moved by another.

Aquinas does not use the term “infinite regress”. Like the label ‘cosmological’ itself, these are terms added by later commentators to his argument. Aquinas says of the relation between things that move from potency to act: “this cannot proceed for infinity” (Hic autem non est procedere in infinitum). His meaning is that the state of affairs cannot be dragged out endlessly to avoid admitting an Unmoved Mover.

The argument against infinite regress is not simply a temporal infinite regress. This is more of a concern for form of the Kalam version of the cosmological argument (at least William Lane Craig’s version of it) but it is not the focus of the First Way.

Aquinas is more concerned about the relationship between things that are ‘moved’ from outside of themselves—things that move from potency to act, from ‘becoming’ to ‘being’. You cannot have an infinite class of things in a state of becoming without anything that brings them into being.

Consider for example a student who is learning a new language you have never heard before. You ask him, “How are you learning to speak this language?” or, in Aristotelian more terms, “What act is bringing about your actualisation as a speaker of this language?”

He replies, “I am being taught by a teacher.” There’s no surprise there; we would expect as much. But imagine his teacher then comes into the room, and we ask her the same question, and she gives the same answer. So far, we’re still not very surprised: just as the student is learning now, so the teacher also needed to learn from someone.

But imagine more and more people kept entering the room and kept giving the same answer. Eventually we would start to wonder, “What is the source of this language? I understand that people are being taught it all over the place, but where does the language come from?”
Even if a billion people all gave the same answer, the same question persists: where did this language come from? You can see that even if an infinite number of people gave the same answer, the question is still not answered.

The problem has nothing to do with time. The problem has to do with the ultimate source of the language: where did it originate? How have these people learnt this language? The question is the same for one person, a million, a billion or an infinite number. All we’re doing by adding more and more people to the explanation is simply postponing the problem.
Aquinas wants to know, what is the source of all being? We do not answer the question by simply adding more and more beings to the argument: the world, the solar system, the Big Band, some quantum fluctuation—whatever. None of them answer the question: what is the source of all actualisation?