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Why an Infinite Regress Among Proper Causes is Metaphysically Impossible

Presuppositions, definitions, and purpose: This article presupposes the metaphysical first principles of non-contradiction, sufficient reason, and causality, which I defended earlier in a Strange Notions article.

By the principle of sufficient reason, I mean that every being has a sufficient reason for its being or becoming. This principle is recognized by virtually all mankind as essential to reality’s intelligibility.

By causality, I mean that every effect (a being whose sufficient reason is not totally intrinsic) has immediate dependency on a cause (an extrinsic sufficient reason). This also I defended in a more recent Strange Notions article. While that article employed common macroscopic examples of simultaneous causality, metaphysical first principles – since they are principles of existence, not of some particular essence – apply equally to submicroscopic physical realities. Nanosecond delays in field propagation between interacting particles do not avoid the metaphysical necessity for contiguity and simultaneous mutual causation between those fields. Nor do claims on behalf of modern physics undermine the classical metaphysical analysis of causality taking place in time as normally understood.1

Since non-being cannot ever produce being, and since the effect, as such, is in continual existential dependence on another for some accidental quality and/or its very existence in being, no effect can survive ceasing to be actively caused – even if that causal agency ceased only a nanosecond ago. Physics is inherently incapable of penetrating the depths of this metaphysical insight about being and causality.

Causes of being and coming-to-be: Metaphysics requires thinking of everything in terms of being, since it is the science of being considered precisely as being. Proper distinctions must be made. For many scientists, because of Hume’s influence, the term, “cause,” means merely an “antecedent” – something always coming temporally before an alleged “effect.” This entails that the antecedent as such cannot be the true cause, since it could cease to act or even to exist before the alleged “effect” appears, which is impossible in terms of principles of being. That is because every true cause must be simultaneous with its effect, since a cause is an extrinsic sufficient reason, and therefore, as St. Thomas says, “To take away the cause is to take away the effect.”2

Yet, an “antecedent” sounds like a cause of coming-to-be. Nonetheless, a true cause of becoming must be simultaneous with that which comes to be. It is not antecedent to it. Thus, a falling dominoes series is an invalid example of a series of simultaneous moved movers, since the first domino may be down before the last one starts to fall. Bearing in mind observations about submicroscopic physical causes made above, a valid example of simultaneous causation of becoming might be a series of contiguous gears in motion simultaneously, so that the earlier move the later in what is, in effect, a single motion. If the earlier gears quit moving, so do the later ones. Even more evidently, if a builder quits building a house, the house does not “finish itself.”

Causes of being appear intuitively more simultaneous, since they do not entail motion which takes place through time. But physical examples are sometimes challenged as being instances of becoming and, alternately, metaphysical instances require philosophical proof, for example, the argument St. Thomas makes that things which can possibly be or not be must be caused to exist.3

The key takeaway from all this is that it simply does not matter whether one is talking about causes of being or of becoming: the causes in both cases must be simultaneous with their effects. When the cause of coming-to-be ceases causing, the coming-to-be of the effect ceases – just as when the cause of being ceases causing, the being effected ceases to exist. Properly understood, causal series of becoming are just as temporally simultaneous as those of being.

Extrinsic causes may be efficient or final. Proper causes are those precisely required to produce a specific effect and prescind from accidental or causally non-relevant associations with either cause or effect. The purpose of this piece is to prove, not God’s existence, but solely that no proper causal regression to infinity is possible. In contrast, a merely accidentally ordered regression, such as the procreative one leading back through all our ancestors, could potentially go on to infinity – as Aristotle appears to say with respect to the possible eternity of species.

Since proper causes must be simultaneous with their effects, temporal causal regressions are irrelevant – including even nanosecond prior submicroscopic “events” that no longer exist. Proper causal regressions at issue are hic et nunc “vertical” -- in the present, not “horizontal” through past time.

Yet, it appears that even such “vertical” regressions can go to infinity. Consider a series in which the being of A is the final effect and B the sufficient reason for A, with C the reason for B, and D for C, and so forth. Since B explains A, and C explains B, and D explains C -- as long as the causally prior reasons regress to infinity, every link in the chain is explained, since each one is explained by the prior link. Since the whole chain is nothing but the sum of all the links and every link is explained, the entire chain is explained and there appears to be no need for a first sufficient reason for the being of A.

Or again, consider such a series from the standpoint of causality as such. We have a final effect which is explained by a regression of intermediate prior proper causes. Other than the final effect, every prior cause is intermediate, since each one is followed by an effect and preceded by its own proper cause. (Remember all causal links exist and act simultaneously in accord with proper causality.) Is there anything about an infinite regression of such intermediate causes that requires a first cause?

Each intermediate cause has two aspects: it is “intermediate” and it is a “cause.” But the term, “intermediate,” refers merely to a subsequent effect and a prior cause. It says nothing about a first cause. And “cause” refers only to a subsequent effect. As long as the causality of each intermediate cause is fully explained by a prior intermediate cause, and as long as the causal regression does not have a beginning point, each intermediate cause is fully explained. Since the whole chain is nothing but the sum of the intermediates, and each intermediate is explained by its prior intermediate, the whole chain appears to be explained without any need for a first cause.

Yet, to understand the opposing and correct side of the argument, imagine a surgical incision in the process of being cut. Since surgeons don’t make incisions with their fingers, a scalpel is needed – essentially to convert blunt motion into cutting motion. Since scalpels don’t normally do surgery by themselves, a hand is needed to move and direct the motion of the scalpel. And an arm is needed to move the hand. While this example is deliberately abbreviated, its initial elements are instructive.

The scalpel, hand, and arm are all intermediate causes. But, what makes them intermediate? What does each contribute to the causal chain? The scalpel contributes sharpness, the hand contributes “holding the scalpel,” and the arm directs the hand. But none are called “intermediate” in virtue of what they contribute of their own nature or role in the series. With respect to what they contribute, they actually act as something of a “first cause,” since what they contribute, they originate for the process.

On the other hand, they are called “intermediate” precisely because of what they do not contribute to the surgical process – something from a prior cause that they simply pass on to a subsequent effect. Each intermediate cause entails two distinct aspects: something they contribute originally to the chain and for which they are something of a “first cause,” and, critically important, something that they do not contribute of their own nature, but which they merely pass on from a prior cause and for which they themselves are termed “intermediate causes.” In the example, it is the motion that passes through the whole chain. As long as nothing but intermediate causes are operative in the chain, each contributes something original – but, and here is the key, none of them contributes that chain of causation or motion that passes through the whole chain and, with respect to which, they are properly called “intermediate causes.” If all such causes are merely intermediate, then some causal activity is passing through the entire chain, but no member of the chain can explain it. Whether the intermediate causes are limited or unlimited in number, they cannot alone explain the causal process that runs through the entire chain. Solely a first cause that initiates the entire chain can do that – a first cause uncaused.

Now, to reconsider that chain of intermediate reasons described above, we see that the same problem arises. The problem is that each prior reason is not really sufficient unto itself. If it were, it would be a first reason, not an intermediate one. It is called intermediate precisely because it is passing along a reason that it itself does not fully explain. Otherwise, the chain would stop right there. If one looks for the sufficient reason of A, it is not fully in B, since B depends on C to fulfill its own reason. If one regresses to infinity in looking at intermediate reasons, the fully sufficient reason will never be found, since none of the intermediate links provides the complete reason for the final effect. Each one leaves some of the needed reason lacking. If one regresses the chain to infinity, the total sufficient reason is never found – and thus, the final effect lacks a sufficient reason. But that is impossible. Thus, there must be a first sufficient reason, which is its own reason – otherwise the principle of sufficient reason itself would be violated.

As for the regression in the chain of intermediate causes, the problem is the same. The argument claims that “as long as the causality of the intermediate cause is fulfilled,” and as long as you never exhaust prior causes, no need exists for a first cause. But the catch is that the causality of each intermediate is not fulfilled in its prior cause, since that cause, too, is dependent on yet a prior cause to fulfill its causality. Regression to infinity means that the causality never gets completely fulfilled, and thus, the chain fails for want of an uncaused first caused.

Let me offer an easily evident example, even if it entails an accidental temporal aspect that is irrelevant in this case. Imagine six people going to a theater together. Imagine that they buy six tickets and walk toward the ticket taker. As the first person reaches the ticket taker, he tells him that the person behind him has his ticket. The next one does the same, and so on until the last person arrives and hands all six tickets to the taker. All is well.

But imagine a different scenario, one in which every person reaching the ticket taker tells him that the person behind him has the ticket. But this time the line of “referrers” is infinite! This means that there are actually no tickets, since no individual person has any tickets! The theater becomes overfilled and bankrupt at the same time!

That is the essential problem with an infinite regress of proper causes. The intermediate causes don’t have any “tickets.” They exist and act only in virtue of passing on some causal process that none of them ultimately originates or completely explains. As causes, they are an ontological welfare class. Whether they are finite or infinite in number, they explain nothing of the thread of causation that runs through them all and links them all together as a causal chain.

Each intermediate cause may contribute something novel to the final effect. Still, what denotes it as an intermediate cause is not what it originates or contributes to the final effect. Rather, it is called “intermediate,” because of what it does not originate or explain of its own nature. It is called “intermediate,” because of what it does not contribute to the final effect -- but rather merely receives from its immediately prior cause and merely passes on to the next cause or final effect.

One could literally write a book on this topic with many more examples and complex distinctions.4 Still, this is essentially the problem of infinite regress among any type or order of intermediate proper causes. Such a regression is simply impossible. One has to arrive eventually at a first cause that has no ontologically prior cause. For an excellent recent peer reviewed article supporting this same conclusion see here.

Again, this is not presented as proof of God’s existence, but merely as proof that an infinite regress among essentially subordinated causes is metaphysically impossible.

Still, if an infinite regression among proper causes of existence (extrinsic sufficient reasons) is impossible, then such a regression, if demonstrated, would require a first cause (extrinsic sufficient reason) which is its own sufficient reason for being – since nothing is prior to it. In other words, the universal principle of sufficient reason would then necessarily imply that at least one thing must be its own sufficient reason for existing. Such a first sufficient reason that fully explains its own existence would be, of course, not a brute fact, since a brute fact is alleged to have no reason at all – either within itself or from another.

An infinite regress among proper or essential causes is metaphysically impossible. And, yes, this conclusion may henceforth be employed as a universally true principle in any proposed demonstrations of God’s existence.


  1. This article assumes the evident truth that real causes produce real physical effects in time, as human beings normally conceive it, that is, with the past no longer existing and the future not yet existing. Eternalists claim that past, present, and future all exist equally, based on special relativity theory’s denial of universal simultaneity for spatially separated events. Were it not for the “need” to conform timelike intervals to eternalism’s false hypothesis, the obvious reading of human experience and scientific observation within the same local world line would be that real causality occurs in “normal” time.  Of course, if that is done, then eternalism as a whole collapses, since all “events” in the cosmos suddenly fall into normal time sequences with the past no longer existing and the future not yet existing, even though absolute simultaneity for spatially separated events is still denied.
  2. Summa theologiae, I, q. 2, a. 3, c.
  3. Summa contra Gentiles, I, ch. 15, no. 5.
  4. Dennis Bonnette, Aquinas’ Proofs for God’s Existence: St. Thomas Aquinas on: “The per accidens necessarily implies the per se,” (The Hague: Martinus-Nijhoff, 1972). The subtitle focuses much of the book on the problem of infinite causal regress.
Dr. Dennis Bonnette

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Dr. Dennis Bonnette retired as a Full Professor of Philosophy in 2003 from Niagara University in Lewiston, New York. He taught philosophy there for thirty-six years and served as Chairman of the Philosophy Department from 1992 to 2002. He lives in Youngstown, New York, with his wife, Lois. They have seven adult children and twenty-five grandchildren. He received his doctorate in philosophy from the University of Notre Dame in 1970. Dr. Bonnette taught philosophy at the college level for 40 years, and is now teaching free courses at the Aquinas School of Philosophy in Lewiston, New York. He is the author of two books, Aquinas' Proofs for God's Existence (The Hague: Martinus-Nijhoff, 1972) and Origin of the Human Species (Ave Maria, FL: Sapientia Press, third edition, 2014), and many scholarly articles.

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