Response To A Tippling Philosopher On Act and Potency

Over at the “A Tippling Philosopher” blog, Jonathan MS Pearce has written a brief post critiquing the Thomistic understanding of actuality and potentiality (or act and potency, or actus and potentia). His aim in doing so appears to be to attempt to undermine the metaphysical foundation of natural law ethics. He writes: “Natural Law philosophy, about which I have talked a great deal recently, owes an awful lot to Aristotle, Aquinas and other thinkers from a bygone era. One of the cornerstones of this essentialist worldview is the pair of ideas of potentiality and actuality” [1]. Pearce has indeed written a fair amount on natural law theory; and we may interact with some of those pieces in future posts. For now, however, let’s focus just on what he has to say about act and potency.

Pearce quotes quite a bit both from the Wikipedia page on act and potency, and from a work by Gunther Laird, to explain the relevant concepts. He then begins his own critique, which, he thinks, “perhaps invalidates the whole differentiation and categorisation of these two ideas” [2]. The first part of his critique contends that the act/potency distinction is incompatible with conceptual nominalism, which he takes to be true:

First of all, I am a conceptual nominalist, as I have set out umpteen times, and this arguably eliminates such metaphysical contortions anyway by saying such mental categorisations are products entirely of the mind and have no ontic existence independent of the conceiving minds in question. Indeed, such nominalism, in my opinion, destroys the foundation upon which natural law, essentialism and Thomistic philosophy and theology is built” [3].

Pearce is certainly correct that conceptual nominalism, as he understands it, is incompatible with Thomistic philosophy generally and the act/potency distinction specifically. However, since Pearce does not argue for conceptual nominalism here (although he does direct us to a different post where he does provide some such arguments), we will leave this objection alone for the time being. Suffice it to say that the Thomist (or those generally sympathetic with Thomism) will of course already reject conceptual nominalism, and so will not be too impressed with an argument from conceptual nominalism against the act/potency distinction. Indeed, the Thomist may take the act/potency distinction itself as good reason to reject conceptual nominalism, rather than the other way around.

But let us leave this point for now and turn to the main objection Pearce offers. This objection is, in essence, that the act/potency distinction is somewhat meaningless given causal determinacy. He writes:

“I want to look at potentiality and relate it to a deterministic or adequately deterministic framework. I would argue that such frameworks equally eliminate the idea of potentiality; or, at least, make potential synonymous with ‘the future'” [4].

Pearce then goes on to examine the example of a caterpillar becoming a butterfly. Given that the caterpillar is “of a particular species and genus” and has a determinate genetic blueprint, and given also its specific environment and other determinate conditions, then “it will invariably turn out in a particular way,” with a determinate coloration, pattern, size, etc. As such, Pearce concludes:

“When we talk about potential, I think we are smuggling in a very human conception about what could be in a very general sense. This butterfly could be of this particular colouration or that particular colouration, it could be of this size, or that size. We line up all the theoretical futures that this butterfly could have given that we don’t know the initial conditions with our limited human minds. However, if we knew every single condition down to every single wave function of the world, then we could predict with surety what the outcome would be” [5].

Pearce then also gives a second example, that of tossing a coin. Before we toss a coin, we might say that “potentially” it could be either heads or tails. But in reality,

“if I was to understand every single initial condition and every single variable at play, on the flip of that coin in that particular instantiation of a coin flip, then actually (pun intended), I would know what the outcome of the coin flip would be. There would literally be no potential head or potential tail but there would be an actual future coin flip of head (for example)” [6].

The idea here is that we really only say the coin could be “potentially” either heads or tails because we are coming to the event of the coin toss from a limited vantagepoint. We lack all of the relevant information about conditions, context, and influences. If we had perfect knowledge of all the relevant factors, we would know that there is really only one possible outcome: the actual outcome. And so Pearce reaches this conclusion:

“Any contextualized thing really doesn’t have the potentiality to be anything other than the exact thing it will be deterministically caused to become, taking into account the causal circumstance it finds itself in. Thus to talk about “Pure Act” and other notions that depend upon this differentiation of potentiality and actuality is somewhat meaningless” [7].

Pearce does acknowledge that this whole argument depends upon a certain understanding of causal determinism; and he doesn’t provide any argumentation for that understanding of determinism in this post. So if one does not accept this account of determinism, the argument against the act/potency distinction shouldn’t have much force (if any). But for the sake of discussion, let’s work here on the basis that Pearce’s account of determinism is correct. Does his argument work given that supposition?

Not at all. Pearce’s argument confuses epistemological possibility (or bare “logical possibility”) with ontological potential. Pearce’s argument makes use of the former, while it is the latter which is the understanding of potentia appealed to in the Thomistic act/potency thesis.

Let’s take his example of tossing a coin. Pearce argues that there is not really a “potential” for the coin to turn up either heads or tells, since the outcome is already causally determined. Let’s say, for the sake of the argument, that this is correct. It still does not follow that the coin does not really have an intrinsic, ontological potentia for its determined outcome. Indeed, it must have this potentia, if the outcome is to happen at all. Suppose the coin is causally determined to turn up heads. We still must say that the coin has the intrinsic potentia to turn up heads; otherwise it wouldn’t be able to turn up heads at all. Even if we were to suppose that the coin lacks any other potential (i.e. cannot possibly have any other outcome), it still must have at least that one potentia, the potentia for its determined outcome. This is so merely by virtue of the fact that, at the present moment (before we toss the coin), the coin has not actually landed heads up yet.

Or take the example of the caterpillar. Even if the caterpillar’s future butterfly coloration is causally determined, it still must have the potentia for that coloration; otherwise that coloration would be impossible. Even given a deterministic account, we must appeal to a real distinction between actus and potentia. If the caterpillar is a caterpillar at t1 and a butterfly at t2, then at t1 it is actually a caterpillar and potentially a butterfly. At t1 it has the potentia for its future coloration, but it does not yet have this coloration actually. Its potentia for its future coloration must be actualized before it becomes actual. And even if this actualization is predetermined such that it must happen and no other outcome can happen, all that this means is that the caterpillar only has one potentia, and no others. But it still must have at least that potentia. Its potentia is still a real feature of its being, and is still really distinct from actus.

Necessity entails possibility. If something must be the case, then necessarily it also can be the case. And potentia is that whereby a thing can be or become something. If causal determinism entails that a particular caterpillar must become a butterfly, it also entails that that caterpillar can become a butterfly, and hence that that caterpillar has the potentia to become a butterfly. Pearce himself seems to recognize this, as he says that on determinism a thing does not have “the potentiality to be anything other than the exact thing it will be deterministically caused to become” (emphasis mine). In other words, even if Pearce’s argument is correct, all that it shows is that a thing does not have more than the one potentia for its determined outcome, not that it has no potentia whatsoever. So, even if correct, the argument does not actually contradict the Thomistic thesis concerning the act/potency distinction.

But we have actually given away too much, even on a deterministic account. For causal determinism does not actually require that a thing have only the single potentia which is for its determined outcome. Rather, all a deterministic account would require is that, among all a thing’s potentiae, there is only one which actually becomes actualized, and this one is determined beforehand by relevant factors/conditions.

Either way, the Thomistic thesis remains unchallenged.


[1]. Jonathan MS Pearce. “Criticising the Idea of Potential and Actuality in Natural Law Philosophy.” A Tipling Philosopher.

[2]. Ibid.

[3]. Ibid.

[4]. Ibid.

[5]. Ibid.

[6]. Ibid.

[7]. Ibid.

5 thoughts on “Response To A Tippling Philosopher On Act and Potency

  1. Excellently written, Harrison. I’m quite surprised that a person who professes to know something about Aristotle and Aquinas could flub potency so badly. I’m a relative newbie when it comes to metaphysics, and even I had no trouble spotting Pearce’s error.


      1. About Aquinas’ Third Way. The argument, as Feser presents it, states that given an infinite amount of time, nothing would exist. Although that could be the case, what guarantees that conclusion? It seems we have an illegitimate move from possibility to certainty.


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