An Evaluation of Thomistic Metaphysics – Part 2.1 – Act & Potency

By | March 1, 2017

My evaluation of Thomistic metaphysics begins where Feser does in his recent book Scholastic Metaphysics: A Contemporary Introduction, namely, with the theory of act and potency.* His chapter on this topic is 57 pages long, so I’ll need to break the topic down into parts. I’m going to parallel Feser’s section numbering to structure my discussion. The section titles, however, are mine. The first half of each section is mainly expository—my focus is on summarizing Feser’s (and Aquinas’s) views with a some of my own explanatory elaboration. The second half of each section is mainly critical and evaluative.

(*Feser’s book begins with a “prolegomenon” (Chapter 0) critiquing scientistic dismissals of metaphysics. Since that topic is tangential to Thomistic metaphysics proper, and since I have little to add by way of either critique or elaboration—it’s a wonderful chapter—I’m going to start with his Chapter 1.)

1.1. Origins of the distinction: accounting for change, persistence, multiplicity, and unity

The act–potency distinction originates with Aristotle, whose metaphysical views were shaped to a large extent by the dialectical context in which he found himself. Feser highlights two of Aristotle’s predecessors, Parmenides and Heraclitus, who came to deeply antithetical and radically implausible conclusions about the nature of change and multiplicity.

Parmenides and his pupil Zeno denied the possibility of change on the grounds that becoming requires the coming into being of something that is not, i.e., something that before the change has the status of literally nothing. And since nothing can come from nothing, change is impossible. Likewise, Parmenides and Zeno were monists who denied the possibility of multiplicity on the grounds that if there were two or more distinct things, they would have to differ in some respect. Since they obviously can’t differ with respect to being, they would have to differ with respect to non-being, which is nothing. And since a difference that amounts to nothing is simply no difference at all, it follows (so they argued) that no two things can be distinct. Hence, there can be at most one thing, namely, the One.

In contrast, Heraclitus (on the traditional interpretation at least) denied the possibility of persistence through change on the grounds that changing things cannot maintain sameness-of-subject-over-time. If A-at-T1 (say, a river) differs in any respect from A-at-T2 (e.g., by containing different water), then the former is utterly distinct from the latter. Hence (so the argument goes), nothing can persist through change. Change involves the ceasing-to-be of one thing and its replacement with something else. Feser suggests (p. 34) that similar reasoning can be used to argue that there’s also no real unity or commonality underlying the diverse manyness of things. What unity there is, is superficial or nominal (à la nominalism), i.e., merely a function of how we group things. What unity we find is something we project, and there is no unity in things for us to discover.

In each case, the positions attributed to Parmenides (no change, no multiplicity) and Heraclitus (no persistence through change, no real unity) are deeply counterintuitive. Being the commonsensical guy that he was, Aristotle wanted a way to do justice to both sets of arguments while avoiding the extreme conclusions of each. Thus, he wanted to affirm both that things can change and that they can persist through change, that there can be both a multiplicity of things and and a real unity or commonality among things. His proposed solution was a theory of act and potency.

The theory says that act and potency are correlative and (importantly) intrinsic principles of persisting substances. Act refers to being, i.e., what a substance actually is at a given time, whereas potency refers to a substance’s potential for becoming. To use a well-known Thomistic example from the First Way, a fire is actually hot—it is in act with respect to being hot—whereas a cold log just placed near the fire is not yet actually hot, but it can become hot—it is in potency with respect to being hot. As the log becomes hot, this potency is actualized. Because the potency is intrinsic to the log, the change takes place in the log. Hence, the log persists through the change (pace Heraclitus). And because the change is a transition between two states of being—from being actually cold to being actually hot—we don’t have something coming from nothing (pace Parmenides). Likewise, because the act of being hot is intrinsic to the log and the fire in each case, there is a real commonality among the two (pace Heraclitus). They both participate in the same act, one essentially (the fire) and the other accidentally (the log). And yet they remain distinct (pace Parmenides) in part at least because they have different potencies. The hot log has the potency to (again) become cold. The fire has no such potency.

My comments on the preceding

In my opinion, this is all plausible as far as it goes. Clearly insofar as anything exists there’s an intrinsic actuality to things. Things that exist do so as this or as that. They exist in some way or other. In all such respects we can say that the thing is “in act” with respect to what it is and how it is, its suchness, if you will. Equally clearly insofar as there is real becoming and persistence through change, there needs to be an intrinsic potency for things to change in the ways they do.

But however plausible this sounds, we should be alert to the fact that act and potency are being used by Aristotle to play (at least) two different sets of roles. The first is as principles of being and becoming. The second is as principles of unity and multiplicity. These two sets of roles, while overlapping, are not obviously coextensive. For example, while potency as a principle for becoming can differentiate between the fire and the log, or between one log and another, it’s not at all clear that potency (so understood) is the only way to differentiate between things and thereby ground multiplicity. Other possible ways of differentiating include, but are not necessarily limited to, spatio-temporal location, haecceities, and intrinsic and relational properties (other than those pertaining to becoming). So it should not be assumed that these two sets of roles (and others that may emerge later) for act/potency must stand or fall together. Indeed, while I think something like the Aristotelian analysis of intrinsic change has got to be right, I’m far less confident when it comes to unity and multiplicity. While the common use of act/potency talk in both domains may serve the salutary function of highlighting similarity and overlaps between the different sets of roles, it also risks conflating things that perhaps ought to be kept distinct. We shall have to keep this possibility in mind as we proceed.

1.1.2. How are act and potency related? 

At this point (p. 36) Feser mentions, but tables until later, the issue of whether act and potency are “really” distinct (Aquinas), “formally” distinct (Scotus), or distinct in some other way.

He also notes (pp. 36-37) and discusses briefly a dispute among scholastics about whether anything other than potency “limits” act. Now this talk of potency “limiting” act strikes me as rather strange. What should we make of it? Feser gives the example of a round, rubber ball. The ball is “in act” with respect to roundness, but it’s not perfectly round—it’s round to a limited degree. It’s roundness is also limited in extent (its size) and to the place and time where the ball exists. Normally I think we’d say it’s the ball’s matter, the rubber of which it consists, that accounts for these limitations. Material objects occupy space and, qua material, have a potency (a susceptibility) to be moved and molded in different ways. They also have a coarseness due to their molecular structure and motion that prevents them from exactly having and holding an idealized shape like sphericity. The ball’s rubber has the potency to be arranged spherical-ishly, we might say, but not the potency to be formed into a perfect sphere.

I get this much, but it’s still not clear how the ball’s, or the rubber’s, potencies “limit” the ball’s act. As we have just seen, potency (of one sort at least) has to do with becoming, and act has to do with being. The rubber’s potencies certainly limit the ball’s potencies, but it’s also the ball’s act—it’s being a round, rubber ball—that determines or “limits” the ball’s potencies. As Feser himself emphasizes (p. 38), actuality is prior to and grounds potency (p. 38), and there can be no potency without actuality. But then why isn’t it more accurate to say that act limits potency, rather than the other way around? The fire and log example above seem to confirm this. The fire is actually hot. The cold log is potentially hot. But the log’s potency for becoming hot is limited by its actual material nature. After all, the log can’t become infinitely hot. After a certain point of heating its molecular constituents will come apart and the log as such will cease to be. So here again it seems that it’s the log’s act, it’s being the kind of thing that it is, that determines or limits its potencies or what can become of it.

Is there a way to make sense of this idea that potency “limits” act? I think so, but to do so we have to bring on board some additional metaphysical baggage that goes beyond the considerations of becoming and multiplicity noted above. Consider this passage quoted by Feser as the second of “twenty-four Thomistic theses”:

Because act is perfection, it is limited only by potency which is a capacity for perfection. Hence, a pure act in any order of being exists only as unlimited and unique; but whenever it (act) is finite and multiplied, there it unites in true composition with potency. (Feser, p. 37)

This presents yet a third conception of act and potency distinct from what has been mentioned so far. Here act and potency are viewed neither as principles of being and becoming, nor as as principles of unity and multiplicity, but rather as principles of perfection and limitation. Feser’s example of the rubber ball gives us a hint on how to make sense of this. Suppose we start by thinking of universals like roundness and humanity as quasi-Platonic entities, namely, as ideal Forms that are in some sense more real and more perfect than the things that participate in them. As is well-known, Aristotle was Plato’s pupil. He rejected the idea that these Forms existed apart from things. Instead of being extrinsic to things, Aristotle insisted that they were intrinsic. Common to all humans is the Form of humanity. The numerically same Form is in each of us. It is our nature or essence, and we all qua human share a common nature. Now let’s suppose that Aristotle’s Forms, like Plato’s, are normative Ideals. The Form of humanity includes all the fullness of what a human being can and ideally ought to be. Since none of us measures up to that ideal, either physically, mentally, or morally, there is a sense in which the Form is more real and more perfect than any of us. If that’s right, then it seems fair to say that we exist as particular limitations of that Form. I take it then that by “a pure act in any order of being” what is meant is an ideal and immaterial instance of that “order of being”. Aquinas famously believed that each angel was an essentially unique “pure act” in its own order of being. But humans are “finite and multiplied”, which raises the question of how the essentially unique and ideal Form that we share can be exemplified in so many, and often less-than-ideal, instances. Aquinas’s response to the question is matter. Matter is mereologically divisible (that’s part of its “potency”) and so can be parcelled out into a multiplicity of finite chunks that, when properly structured, can each severally exemplify a common Form. Each instance of humanity is therefore a “composition” of Form (act) and Matter (potency).

My comments on the preceding

In the first place, it should be noted that this new role for the act/potency distinction is not obviously coextensive with either of the other two. It is not obvious, for example, that becoming entails limitation or imperfection. Nor is it obvious that multiplicity under a common universal must come by way of limitation. Perhaps there are good arguments for making these connections—and I grant that once we accept the broadly Platonic framework as modified by Aristotle these connections are not implausible—but absent a positive proof of such we should keep in mind the possibility that Aquinas’s use of the act/potency distinction in these three different ways conflates things that ought to be kept distinct.

The broadly Platonic framework as I’ve sketched it provides a way of understanding how matter is at once a principle of multiplicity and a principle of limitation. It also helps us understand how there can be a real commonality among things–they have the same Form–that are nevertheless different in a wide variety of ways. This is an idea that should be very attractive to anyone who believes in universal human rights. To be human, for example, is to intrinsically possess the Form of humanity. Any being that has that Form, regardless of its physical, cognitive, or even moral limitations, is still fully human. I strongly endorse this idea.

Granting, then, that matter can be a principle of multiplicity and limitation, I still don’t see why multiplicity in every “order of being” must be purchased via limitation (departure from an essential ideal) and materiality. Why can’t angels (or electrons), for example, share a common order of being and be distinct by something other than matter, e.g., spatial location, haecceities, non-essential intrinsic properties, or something else? (Like Aristotle, Aquinas probably wouldn’t have viewed matter as really distinct from space. It wasn’t until the 16th century with the experiments of Pascal and Torricelli that the possibility of a vacuum or space without matter became widely accepted.) Nor is it clear why we should identify either God or angels as instances of “pure act” in their own unique order of being. If angels can change (cf. Lucifer’s fall), then they require potency for becoming, at least initially. Why can’t the same be true of God as well? (This issue will come up again later.)

1.1.3. Divisions of act and potency

According to Feser (pp. 38ff.), potency can be subdivided into objective (i.e., merely conceptual) and subjective (i.e., real) potency. The latter, in turn, can be subdivided into active and passive potencies. Active potencies are better called “powers” because they are capacities to bring about effects, whereas passive potencies are capacities to be affected and changed. That the same term “potency” should be used for both active and passive potencies is both confusing and misleading. As Feser notes, it is passive potency that is potency in the strict sense that contrasts with act. So God who, according to Aquinas, is Pure Act is (qua omnipotent) loaded with active potency but utterly without passive potency. Hence, God is absolutely impassible and immutable (i.e., can’t be affected or changed).

Feser goes on to detail several distinctions with the category of passive potency, as well as several distinctions within the category of act (pp. 40–41). Here’s an image that someone else prepared based on Feser’s book:

Divisions of Act and Potency

Divisions of Act and Potency

For now I will only comment on the distinction between pure and mixed act. For Aquinas, both God and angels are pure act (actus purus). But God is absolutely pure act, whereas angels are only relatively pure. An angel is pure act because it is “form without matter”, but it is only relatively pure because its essence is in potency relative to its existence. God, in contrast, simply is His existence. His essence and His existence are one and the same, so the former can’t be in potency relative to the latter. Humans and rubber balls, of course, would be instances of mixed act.

My comments on the preceding

The issue of the relation of existence and essence will come up again later when we get to Feser’s chapter 4, but it is worth noting that the idea that angelic essences are in potency relative to their existence introduces yet a fourth set of roles for the act/potency distinction. For here we’re not talking about potency as a principle of becoming, or potency as a principle of multiplicity within an “order of being”, or potency as a principle of limitation in relation to an order of being, but potency as a principle of existential limitation. Feser doesn’t spell it out here, but the underlying idea is that being, pure unfiltered being, which is God, has to be limited by a creaturely essence in order for anything other than God to exist. Being being limited in a certain way is what defines the creature’s essence, its order of being.

Summing up, then, we have (so far at least) four different sets of roles for act and potency:

Act Potency Posited to account for
being becoming intrinsic change
unity (form) multiplicity (matter) multiplicity (within an order of being)
perfection limitation limitation (with respect to a form)
existence essence limitation (with respect to being)

As I have noted above, it is far from obvious that these different applications of the act/potency distinction must stand or fall together. At the very least, there seem to be ways other than matter to account for multiplicity within an order of being. Moreover, limitation with respect to a form seems to require a broadly Platonic way of thinking about universals (Forms), which holds that Forms are more real and more perfect than their instances. (At the culmination of the Platonic heirarchy is the Form of the Good, which virtually contains all of the perfections of all of the other Forms. In later middle-platonic and neo-platonic thought, the Form of the Good became identified with God.) Likewise, limitation with respect to being presupposes the idea that being comes in degrees—something can be more or less real. These ways of thinking about universals and about being are not obvious and would be denied by a great many philosophers today. Most philosophers today would insist that being does not come in degrees but is categorical—something either is or it isn’t (full stop). Likewise, most philosophers would see universals as supplying merely necessary and sufficient conditions for kind-membership, not as quasi-Platonic Forms virtually containing the “fullness of being” of their instances. Hence, they would argue, multiplicity within a kind can be accounted for by addition (e.g., of non-essential properties) rather than by subtraction (i.e., limitation). Of course, that most modern philosophers disagree with Aquinas on these issues doesn’t make Aquinas wrong, but it does mean that we should require something substantial by way of argument before we accept the full metaphysical framework of act and potency sketched above.

9 thoughts on “An Evaluation of Thomistic Metaphysics – Part 2.1 – Act & Potency

  1. Josh

    Dr. Rhoda,

    Thanks so much for these blog posts! As someone who works in the Thomist metaphysical tradition, it is extremely helpful for me to see what critics pinpoint. I wanted to make a brief comment about your remarks re: Aristotle’s use of act/potency to account for unity/multiplicity and its relation to Thomas.

    I think there is quite a bit of evidence to suggest that Thomas’ goes beyond Aristotle on this point. Although I haven’t quite been able to convince my fellow Thomists of its relevance, Thomas says very clearly on a number of occasions that multiplicity properly speaking is a transcendental feature of being qua being (multitudo est de transcendentibus). That is to say, just like unity/truth/goodness, etc. , “multitudo transcendens” is a positive perfection of being itself–as opposed to a mere “privation” of unity.

    Now this doesn’t mean that Thomists should toss the idea that creatures are formally distinct from one another by virtue of their degrees of perfection. On the contrary, Thomas clearly holds something like the “Platonic” position you describe above. But the lesson of multitudo transcendens (which is absolutely original to Thomas) is that this is not all there is to say about multiplicity. Indeed, the fact that creatures are distinct in terms of act/potency belies the fact that they are a *deficient* multiplicity in comparison to God’s *perfect* multitudo (in the absolute *equality* of the community of Persons).

    Anyway, I don’t want to ramble on about this, but I’m writing a dissertation on the topic, so it’s tempting. 🙂

    Thanks again for these great posts!

    1. Alan Rhoda Post author

      Hi Josh,

      Thanks for your constructive comments. I welcome your further interaction with me on this and future posts.

      Regarding the idea that “multiplicity properly speaking is a transcendental feature of being qua being” I’ve never heard about this. I can see how it could be viewed as an entailment of Thomistic metaphysics + Trinitarianism. And I presume there’s a story to tell about how this sort of multiplicity is compatible with divine simplicity. What’s not clear to me is how it might be relevant to beings other than God.

      Best wishes regarding your dissertation.


  2. Tom

    “[Feser] also notes…and discusses briefly a dispute among scholastics about whether anything other than potency ‘limits’ act. Now this talk of potency ‘limiting’ act strikes me as rather strange. What should we make of it?”

    Totally agree with your response to this. Actuality defines and delimits potentialities, not the other way around. By turning it around I can only imagine Feser is describing the sense in which one can reason from a thing’s potentialities to the kind of thing it actually is. Maybe. Or perhaps he just wants to say that a thing’s potentialities limit its act in the sense that the potencies inherent in its act de-‘limit’ (define, describe) what its act might or might not become; kind of like walking backwards into the truth that ‘actuality delimits potentiality’. Not sure.

    I’m excited you’re doing this Alan. Looking forward to it. As you know I’ve come to appreciate a lot about classical metaphysics (which we know isn’t convertible with Thomism, but he’s as good a place as any to lay out the issues). And to anticipate a question I’m sure you’ll get to – Do we want to say (with Process folk) that God’s ‘act’ (his concrete actuality) is entirely and without remainder contingent becoming whereas the divine perfections (omniscience, goodness, etc.) are (as Hartshorne argued) mere ‘abstractions’? But just as actuality grounds/delimits potentialities, so also does actuality determines/grounds abstractions. So we have to posit, it seems, some necessary, antecedent actuality. But I’m getting ahead of things. Very interested in seeing where you come out on this.

    No pressure! We just want you to solve 2,000 of theological mystery!


    1. Scalia

      A potential limits act in that the actualization of potency is limited to its essence. Potency/Act is also known as Essence/Existence. An oak tree’s essence will not allow it to become a rational animal. Its act is thus limited by its potential.

  3. Jeff

    Good to see you posting again, Alan!

    With respect to your comment that “Of course, that most modern philosophers disagree with Aquinas on these issues doesn’t make Aquinas wrong, but it does mean that we should require something substantial by way of argument before we accept the full metaphysical framework of act and potency sketched above,” I’m thinking that many philosophers simply see no point in violating inductive criteria (not necessarily consciously, of course) like parsimony and breadth of explanation when accounting for those beliefs that we can’t seem to abandon without being logically inconsistent or unintelligible in some way. That being the case, it’s hard to see from that point of view what the language of “actus purus,” impassibility, etc. buys us which can’t already be accounted for with the much clearer language of existence, substance-attribute relationship, locality, temporality, causality (including teleology), etc that main-stream philosophy has been using for centuries.

    Hopefully, when you’re done we’ll see more clearly if those philosophers are right. If so, a remaining question will be whether inductive criteria are to only be applied to certain subject matter (and why, if so) or all subject matter where it can be applied.

  4. Thomas

    There’s a long-standing issue with defining act and potency in terms of change, or else mental operations (such as definition and judgment). St. Thomas primarily employs the latter (for an extended textual argument, see John Wippel’s work). And there’s a secondary issue in which sensible form and intelligible form are not adequately distinguished.

    Feser, to my mind, tends to muddy the issue by relying more on sensible change than the relevant mental operations to try to make act/potency distinctions. It clarifies the matter greatly to rely as St. Thomas (and arguably Aristotle) do by correlating matter, form, and actuality to the relevant mental operations.

    On this view, form is what is understood in that moment of illumination where something “clicks”, and then is elaborated in an explanatory (i.e., scientific) theory. Matter are those elements of the given which form explains; it’s what is known only indirectly under a theory via observation. Finally, any theory may be incorrect. What is known by ascertaining whether our theoretical understanding is correct is actuality, existence.

    The relations, then, of potency to first actuality (i.e, form) is strictly analogous to the relation between the elements of a problem to a solution. The relation of first actuality to second actuality (existence, occurrence) is strictly analogous to the difference between a solution that is merely hypothetical and one that is verified as correct. For example, think of the difference between consider the proposition “Space is relative to observers”, and grasping that it is correct. The additional content you grasp in moving from consideration to knowledge of its truth is a direct grasp of what actually is.

    Matter, form, and act are ultimately placeholders, lines that are filled in by the explanatory sciences. Without grasping their correlation to the relevant mental acts, talking about act and potency are, at best, confusing. The limitation of form simply has to do with particular role played by terms in an explanatory theory, for instance. Otherwise it sounds like a quasi-quantitative constraint.

    1. Alan Rhoda Post author

      Thanks for the engaging comment, Thomas.

      I should probably look at Wippel on this as you suggest, but offhand your idea that the act-potency distinction is primarily to be understood in terms of mental operations strikes me as more in the style of transcendental neo-Thomism à la Bernard Lonergan than Aquinas himself. Lonergan uses the term “insight” to refer to what you call “the moment of illumination”. He uses the term “judgment” to refer to what you describe as “ascertaining whether our theoretical understanding is correct”. There is an analogy between the Lonerganian triad of experience, understanding, and judgment and the Thomistic triad of matter, form/essence, and existence.

      PS. I read of lot of Lonergan while in grad. school. He and Charles Peirce were two of my favorite philosophers. I lost some of my enthusiasm for Lonergan after I read his non-solution “solution” to the problem of creaturely freedom and divine sovereignty. But I still think his “cognitional theory” is basically correct, and very compatible with Peirce’s logic of inquiry.


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