I. Introduction

Perfectionism is the view that what is intrinsically good is the fulfillment of human nature.Footnote ¹ A good human life consists in the development and exercise of the characteristic human capacities, including our physical, intellectual, volitional, social, and emotional powers, as well as the realization of their corresponding ends, such as life and health, knowledge, free agency, friendship, and beauty. In a recent article, “Problems for Perfectionism” (Bradford Reference Bradford2017), Gwen Bradford catalogues the most common objections to the theory. She offers replies to many of the traditional objections, but presses one that she thinks is the most difficult to answer, which she calls the “Deep Problem” for perfectionism: explaining why the fulfillment of human nature is good. She examines multiple strategies for handling this problem, but she does not give a definitive solution and leaves it an open question. Bradford's challenge has so far gone unanswered, and contemporary perfectionists have not offered a solution to the Deep Problem.Footnote ² We take up that task in this article. We propose a solution to the problem, one that is drawn from an older philosophical tradition and has not been explored in recent literature. We argue that by situating perfectionism within a Thomistic metaethical framework in which perfection is understood as a fullness of being, and in which being is convertible with goodness, we have a solution to the Deep Problem and an explanation for the goodness of nature fulfillment.

II. The Deep Problem for perfectionism

The Deep Problem is the challenge of explaining why the fulfillment of human nature and the development and exercise of human capacities is good. Bradford states it the following way:

She thinks this is the hardest question for perfectionists to answer, and that no satisfactory answer has been given.

Bradford examines various possible solutions to the Deep Problem, three of which are relevant for our purposes in this article. The first is the “Tu Quoque” reply: all theories of well-being face the same problem of explaining why the ultimate good-making property is good, so the problem is not unique to perfectionism but instead is a question every value theory must answer. Guy Fletcher puts the point well:

The second option is the “Further Theory” response that grounds perfectionist value in a different and more fundamental kind of value. This deeper value theory is supposed to explain why nature-fulfillment is good. As Bradford describes it, “We appeal to this further theory of value, not human nature, which in turn explains why our developing human capacities is good: human capacities instantiate this other value” (2017: 356). The example she considers is Robert Nozick's view that organic unity is the more ultimate value that grounds perfectionist value: developing and exercising human capacities is good because it instantiates the value of organic unity (Nozick Reference Nozick1981).

Third, there is the “Aristotelian Flourishing” approach, represented by Richard Kraut (Reference Kraut2007). According to Bradford,

Bradford rejects the Further Theory and the Aristotelian Flourishing strategies; we will discuss her objections in Section IV and explain how our approach overcomes them. Her main answer to the Deep Problem is the Tu Quoque response. On the one hand, we agree with her that this reply effectively neutralizes the problem in the dialectical context of competing value theories. On the other hand, it is not a very satisfying solution to the problem itself. We want to understand and explain things as much as we can, and it is far from obvious that the Deep Problem is asking for an explanation that in principle cannot be discovered. Michael Prinzing, in a recent article defending the explanatory significance of perfectionism, says:

Like Prinzing, we believe that a deeper explanation of perfectionist goodness is something we ought to seek, because, philosophically speaking, a more ultimate explanation is always desirable. We will offer a more satisfying answer to the Deep Problem than the Tu Quoque response, one that is not merely a negative defense that blunts the force of the problem, but a positive proposal that solves the problem. Our solution to the Deep Problem combines the two other strategies Bradford identifies – Further Theory and Aristotelian Flourishing – and grounds both in a Thomistic metaethical framework.

Before laying out this framework, we should mention one of Bradford's reasons for rejecting the Further Theory response, which is simply that an adequate theory has not yet been suggested. She dismisses Nozick's version because his organic unity theory of value has few proponents (Bradford Reference Bradford2017: 356). She then issues an open invitation for a different kind of approach, saying:

We aim to make good on this promissory note by offering a better candidate for a further theory, one inspired by the thought of Thomas Aquinas.

III. Thomistic metaethics

To lay the groundwork for the Thomistic solution to the Deep Problem for perfectionism, we will give a brief outline of the foundation on which Aquinas develops his understanding of goodness. While the term ‘good’ can be used to refer to many things for Aquinas, the central concept of goodness is deeply rooted in his metaphysics. In fact, this may be an understatement, for, traditionally understood, metaphysics is the study of being qua being (i.e., the study of being as such, or being just insofar as it is being), and, on Aquinas's model, being and goodness are convertible – that is, they are ultimately the same reality. So, in this sense, metaphysics just is the study of goodness. The doctrine that being and goodness are convertible is not unique to Aquinas. It was commonplace in ancient and medieval philosophy to affirm the convertibility of all the “transcendentals”: being, goodness, unity, truth, res (thing), and aliquid (something).Footnote ³ Indeed, this is a position that arguably can be traced back to Plato, and it is espoused by prominent thinkers such as Augustine, Boethius, Pseudo-Dionysius, Avicenna, Albert the Great, and John Duns Scotus, to name only a few (Aertsen Reference Aertsen1985, MacDonald Reference MacDonald and MacDonald1991).

Yet while there is a rich discussion concerning the transcendentals throughout the ancient and medieval periods, we will focus exclusively on Aquinas's understanding of the convertibility of being and goodness, which, following David Oderberg (Reference Oderberg2014), we will call “the convertibility principle.” Aquinas expounds this doctrine as follows:

Here Aquinas makes it clear that the terms ‘being’ and ‘goodness’ express different things, that is, they are different in sense, a point which holds for all the transcendentals. Nevertheless, ‘being’ and ‘goodness’ are not different in reference, but are one and the same thing. To put this in terms of another contemporary distinction: being and goodness differ in intension, but have the same extension; they do not have the same meaning, but they designate the same thing in the world. While it may not be appropriate in all cases to use the terms ‘being’ and ‘goodness’ interchangeably, they ultimately refer to the same reality (Stump and Kretzmann Reference Stump, Kretzmann and Morris1988, Stump Reference Stump2003: ch. 2, Oderberg Reference Oderberg2014). As Aquinas notes, goodness is being under the aspect of desirability, rather than under the aspect of truth, unity, etc.

The convertibility principle has struck many contemporary philosophers as confusing, and occasionally as something we can easily dismiss. For example, Thomas Hurka, the most prominent defender of perfectionism, says this about the doctrine:

One may be inclined to agree with Hurka that the convertibility principle is both perplexing and useless, and therefore ought to be dismissed. Further, there appears to be an even more fundamental objection we can level at it than the claim that it is a mere “rhetorical flourish.” It seems clear that many things that fall under the category of “being” (which includes quite literally everything that exists) are not good. For instance, disease, loneliness, and moral atrocities are all bad, even though these things clearly exist. We can call this the Bad Being Objection. So, besides the apparent uselessness of this principle, is it not also obviously false?

While these objections may strike one as intuitive, we suggest that they are rooted in a failure to understand and appreciate the significance of Aquinas's claim. To see what we have in mind, it is important to consider select features of Aquinas's conception of being. Aquinas adopts Aristotle's distinction between potentiality and actuality, the former of which refers to a thing's ability to undergo some kind of change, and the latter to the way a thing is before or after a change has occurred. While there are many ways that something can undergo change, one that is especially important for our purposes concerns the capacity (i.e., power) of a given thing “to be in a different and more completed state” (Cohen and Reeve Reference Cohen and Reeve2020), which is commonly referred to as a power in “first actuality” on the Aristotelian-Thomistic model. To illustrate this notion of first actuality, consider a cheetah cub. Like any other material substance on the Aristotelian-Thomistic model, a cheetah cub has a nature that makes it the specific kind of thing it is and that confers upon it a set of characteristic capacities.Footnote ⁵ Yet even though this cheetah cub counts as a genuine instance of a cheetah, there is also a clear sense in which it lacks some of the defining features of that species. For example, a cheetah is the fastest land animal, having the ability to run at a speed of approximately 70 miles per hour, but this cub is incapable of running at this speed at her current stage of development. When she becomes larger and stronger, though, she will then develop the capacity to run at high speed. Once she develops this capacity, there is an important respect in which she now exists in a more complete state as a member of her species, for she can now exercise a characteristic power of her species. Nevertheless, even though coming to possess this capacity makes the cheetah a more complete cheetah, clearly she is not always running at 70 mph. When the fully-grown cheetah is lying on the savanna, for example, she is not exercising her capacity to run fast, and thus she is in a state of potentiality regarding this capacity. To put this in terms of the Aristotelian-Thomistic model, when she is not running she has the power to run fast in first actuality. When she is running at top speed, she has actualized this capacity, and therefore has the capacity in second actuality. Hence we can conceive of a capacity in first actuality as a power possessed by a specific kind of thing that is not currently exercised, whereas that capacity in second actuality is that same power fully actualized (Aristotle, Metaphysics: IX.61048a25, cf. Stump Reference Stump2003: 65–67).

While the foregoing is an important feature of the Aristotelian-Thomistic powers ontology, there is a further aspect of this conception of first and second actuality that has important implications for our purposes. For Aquinas, as well as for Aristotle before him, when something actualizes a power that is characteristic of that given thing – that is, when it exercises its capacity in second actuality – it is now a fuller manifestation of what it is to be that thing. To put this differently, in the same way that becoming an adult cheetah and thereby developing characteristic capacities actualizes a cheetah as an instance of its kind, to exercise those powers in second actuality (i.e., to actualize those powers) is also to become a more perfect, or more complete, thing of that kind.

To understand what Aquinas has in mind, instead of referring to our cheetah as a “cheetah,” we could refer to her as an instance of “the fastest land animal.” Of course, as noted, the fastest land animal sometimes lies on the savanna, in which case she has the power to run fast in first actuality. But when this fastest land animal actualizes her ability to run fast, she now has this power in second actuality, and has actualized herself more fully qua fastest land animal. And this is key, because actualizing her capacity to run fast brings the cheetah into a more complete or perfect state of being given the kind of thing she is. In this sense, to actualize a characteristic capacity just is to bring a given thing into a more complete or perfect state for that kind of being. And this is precisely what this conception of actuality amounts to: the greater perfection of a substance through the realization of its characteristic powers (Stump Reference Stump2003: 66–67). To actualize a power for a given thing is for that thing to become more complete, which is to say that it makes it to be more fully as the kind of thing it is. Here is another way to put it: for Aquinas, being just is actuality/completion, and while one must first have a power in order to actualize it, and therefore must already have some degree of actuality (i.e., must exist) regardless of whether a given power is actualized, something can be brought into a greater degree of completion when it exercises its powers. The cheetah that is lying on the savanna is still fully a cheetah even though it is not manifesting its power of speed, but it can more fully actualize what it is when it develops and exercises that power.

Aquinas raises an objection to the convertibility principle that touches on an important objection to the metaphysical doctrine outlined above, the answer to which helps to clarify this principle. One might notice that this ontology implies that a thing can, at least seemingly, exist to a greater or lesser degree. After all, if exercising a power (i.e., having a power in second actuality) brings a given thing into a more complete state, that appears to suggest that the thing exists more fully when its powers are utilized. But ‘being’, it would seem, is an all-or-nothing term. That is, something either exists or it doesn't, so we cannot make sense of something existing more or less fully. Here is how Aquinas states this objection: “[G]oodness can be more or less. However, being cannot be more or less. Therefore goodness differs from being in reality” (ST I, Q. 5, a. 1, obj. 3). Hence, being and goodness are not convertible. We can call this the Binary Being Objection.

In responding to an objection of this sort, Aquinas draws a distinction between what we can call “being simpliciter” and “qualified being”: “[B]y its substantial being everything is said to have being simply (ens simpliciter). However, through any additional actuality something is said to have being with qualification (esse secundum quid)” (ST I, Q. 5, a. 1, ad 1). Just insofar as something exists, it has being. Hence regardless of whether any of its characteristic powers are actualized, something can still be said to exist in this sense. Nevertheless, when that thing actualizes its powers, it achieves more “qualified being.” Yet it is important to note that “qualified being” does not stand in contrast to “being simpliciter,” as if these are two genera or species of being. Indeed, given that “being” is not a genus in the first place for Aquinas, this cannot be what he has in mind (Summa contra Gentiles (SCG) I, c. 25; Aquinas Reference Aquinas1918). Rather, what Aquinas is getting at concerns the degrees of actualization of a given thing.Footnote ⁶

To cash out the distinction between being simpliciter and qualified being, return to the cheetah example, but imagine that our cheetah has been put into a state of total stasis. Such a cheetah is not exercising any of her powers, and therefore all of her powers exist in a state of first actuality. Clearly this cheetah still exists, and clearly she still counts as a cheetah, even though she is not operating in any of the ways characteristic of her species. To have being in this sense is to have actuality (since these are the same thing), and thus it is only necessary that something has the bare minimum of actuality to exist. So, when speaking of “being simpliciter,” even the cheetah in a state of complete stasis exists. But setting aside the bare existence of that cheetah, she is nevertheless as unactualized as a cheetah can be. When the cheetah wakes up and begins to exercise her characteristic powers, she becomes a more fully actualized member of her species, and thus has more “qualified being.” So, when Aquinas refers to being simpliciter and qualified being, he is ultimately seeking to express the various degrees to which something is actualized. Once we recognize that being just is actuality, it becomes clear that there is, in fact, an important sense in which a thing can exist to a greater or lesser extent.

To say that everything that exists is good is to say that all existing things, in virtue of having being simpliciter, also have goodness in the first, all-or-nothing sense.Footnote ⁷ To say that things of the same kind differ in goodness is to speak of being in the second sense of qualified being, which is a matter of degree. This analysis shows how Thomistic metaethics can overcome the Binary Being Objection. The fact that goodness comes in degrees is not a reason to think it is inconvertible with being, because, as Aquinas would say, both goodness and being “can be more or less.”

With this brief metaphysical background in place, we suggest that it becomes much easier to understand the convertibility principle, as well as to recognize the value of Aquinas's metaphysics of goodness for a perfectionist axiology. In Thomistic metaethics, the most fundamental kind of goodness is metaphysical goodness: goodness understood as the actualization of potentiality. Metaphysical goodness is goodness simpliciter, the primary and most basic kind of goodness. All other types of goodness – prudential, attributive, moral, etc. – ultimately can be analyzed in terms of metaphysical goodness.Footnote ⁸ Perfection, on the Thomistic approach, is understood as metaphysical goodness. Aquinas says that “the perfection of each thing is its goodness” (SCG I, c. 38) and “something is perfect insofar as it is in actuality” (SCG I, c. 39). As Oderberg puts it, a perfection is “an increase in the fullness of being, a bringing to fulfillment or completion of some disposition, power, or tendency of an object – in scholastic terminology, the actualization of some potentiality (or potency) of a thing” (2014: 346).

Indeed, since “perfection” on the Thomistic model is the same thing as “actuality,” and since “actuality” is the same thing as “being,” anything that exists (being simpliciter) has some degree of perfection just in virtue of existing. To adapt an earlier distinction, we can think of this sort of perfection as “perfection simpliciter.” But insofar as there is a distinction between “being simpliciter” and “qualified being,” there is also a distinction between “perfection simpliciter” and “qualified perfection.” The latter refers to the actualization of a characteristic natural capacity that makes a thing a more ideal and complete instance of its kind (i.e., makes it exist in second actuality). In light of this, anything that exists has perfection to some degree and therefore is good. It is also good when a thing actualizes its characteristic potentialities and thereby comes to exist in a more complete state, which is to say becomes more perfect (i.e., has more “qualified perfection”). As will become clear in the following section, we are primarily interested in this latter sort of perfection, for this is what enhances the goodness/being of a thing and determines its degree of nature-fulfillment and flourishing, and therefore is relevant to Thomistic perfectionism as a theory of well-being.Footnote ⁹

Now we are in a position to answer the Bad Being Objection, raised at the beginning of this section, which claims that Aquinas's metaethics cannot account for the fact that some existing things are not good. While the convertibility principle entails that no particular thing could be bad in every respect (after all, if being and goodness are convertible, then to have being is to have goodness), it does not follow that all beings are good in every respect. Indeed, as is clear from experience, there are many natural and moral evils in the world, and therefore many things that are not good but bad, including disease, loneliness, and moral atrocities. If the convertibility principle is correct, then these evils can be explained, at least in part, by the fact that an entity lacks something that would make it a more perfect member of its kind. In other words, a bad thing is bad, at least in part, because it has less qualified being as a result of failing to actualize its natural capacities.

This reply to the Bad Being Objection calls attention to one final aspect of Aquinas's metaethics: the doctrine of evil as a privation, which is not really a new addition to the metaphysical system we have sketched, but rather a corollary of it. On the Thomistic model, metaphysical evil – badness in its most general and fundamental sense – is analyzed in light of metaphysical goodness. Aquinas says that,

Metaphysical evil is not the mere absence of being/goodness, but the absence of some being/goodness that a thing ought to possess given its nature. Evil is a privation rather than a mere absence. That is why, for example, the inability to run is bad for a cheetah but not for a maple tree, and the inability to run at 70 mph is not bad for a human being like it is for a cheetah. The idea is not that if something lacks any sort of being at all it is therefore bad. Instead, something is bad because it lacks some characteristic perfection that it should have, where the standard of how a thing should be is determined by its nature; it lacks the qualified being that is realized when it actualizes some characteristic capacity. Applied to the examples from earlier: disease is a privation of the physical good of health, loneliness is a privation of the social good of friendship, and moral wrongdoing is a privation of the volitional good of virtue or right order in the will.Footnote ¹⁰

The foregoing outline of Thomistic metaethics shows why the convertibility principle is plausible – or, at least, why it is rendered more plausible by our exposition of it and rebuttal of objections to it. If goodness simply refers to that which is perfect or complete, and if that which is perfect or complete is a more fully actualized thing, then insofar as being is actuality, it follows that being and goodness are really the same thing. Of course, being refers to actuality, whereas goodness refers to actuality qua desirable; but even though they are different in sense and are viewed from two different perspectives, they are the same in reality. In fact, given this framework, not only is the convertibility thesis plausible, it is difficult to see how one might try to reject it. If we wish to suggest that goodness is different from being, then we owe an explanation for what this difference is. After all, being (actuality) is the broadest “category”Footnote ¹¹ possible, for everything that exists has being (actuality), so if goodness is not the same as being then it must differ from being in some way. The claim that it differs from being by having something in addition to being is incoherent, for then there would have to be something that is outside the scope of being; this would be to say that it is some actuality beyond actuality. If we wish to say that goodness has being but is distinguished from being, then there must be some difference that distinguishes goodness from being. But then either that difference is not being (actuality), in which case it does not exist (it is not actual) and therefore cannot be that which distinguishes goodness from being, or else that difference involves some lesser degree of actuality, which, as noted above, means that the difference makes the thing in question less perfect, in which case it becomes difficult to see why (or how) we would still call that difference “good.” Indeed, once we understand Aquinas's account of being and goodness, it appears to be analytically true that being and goodness are convertible.

There is, of course, much more that can be said about the convertibility of being and goodness, and about Aquinas's metaphysics of goodness in general. However, even though we think Aquinas's theory of goodness is correct, our goal is not to defend his position but to show that it provides a solution to the Deep Problem for perfectionism. Thus, our argument is conditional in nature: if Thomistic metaethics is correct, then we have a satisfactory answer to the Deep Problem. We agree with Hurka's earlier remark that this metaethical framework can sound strange, especially to contemporary ears. But, contra Hurka, we argue that it does add something important to perfectionism, and that it gives perfectionism a new metaethical foundation that enables it to overcome the Deep Problem. Far from being “an obviously expendable accretion,” it is a valuable addition to the standard perfectionist approach.

IV. A Thomistic solution to the Deep Problem

The metaethical framework sketched in the previous section provides the building blocks for an answer to the Deep Problem for perfectionism. We have seen that in reference to something like humans (or any living thing), the actualization of a natural capacity is perfective of that thing, which is to say its actualization increases the goodness of that thing. As a result, it is true by definition that the actualization of some capacity is good, and thus the question regarding why developing human capacities is good is one that already contains its own answer. The basic explanation of why nature-fulfillment is good is that the fulfillment or perfection of human nature consists in the actualization of human potentialities or fullness of human being, and since being is convertible with goodness, the perfection of human nature is good.

An important feature of Thomistic perfectionism is its fusion of the metaphysical and the normative, which circumvents the potential objection that we are offering a metaethical explanation whereas the Deep Problem is asking for a normative explanation. On a Thomistic approach to axiology, there is not a hard separation between metaethics and normative ethics because all normative theories of value ultimately bottom out in metaphysics. If we begin on the normative side and ask the question “what is good and why?”, we start with intuitions about the various things that are good (e.g., health, knowledge, friendship). Then we seek a theory to explain their goodness. Perfectionism says that what is good is the fulfillment of human nature, understood as the development and exercise of the characteristic human capacities and the realization of their corresponding ends. This is a normative thesis about the nature of prudential goodness. Alternatively, if we begin on the metaphysical side, we start at the most fundamental level of being (we cannot go any further, for there is nothing more foundational than being). Then we recognize the convertibility of being and goodness and introduce the notion of metaphysical goodness understood as the actualization of potentiality. Then we home in on human beings and analyze human metaphysical goodness in terms of the actualization of human potentialities, which is equivalent to the development and exercise of the characteristic human capacities and the realization of their corresponding ends. This is a metaphysical thesis about the nature of metaphysical goodness.

Whether we start at the normative or the metaethical level, we arrive at the same place. The normative thesis is the same as the metaphysical thesis in the sense that both affirm that the development and exercise of the human capacities and the realization of their corresponding ends is good – both prudentially good and metaphysically good. The explanation given by Thomistic perfectionism is both normative and metaphysical at the same time, and the two realms are linked due to the fundamental nature of reality itself and the convertibility of being and goodness. The convertibility principle is a metaphysical-moral principle that concerns something non-normative (being) and something normative (goodness).

Earlier, we said that the Thomistic solution to the Deep Problem embodies two of the strategies identified by Bradford. The first is a Thomistic “Further Theory” response. The heart of this response is the convertibility principle. Aquinas's moral metaphysics, with its central thesis that being and goodness are convertible, is a deeper value theory that explains the value of nature fulfillment. All types of goodness, including prudential goodness, are analyzed and explained in terms of the actualization of potentiality; metaphysical goodness is goodness simpliciter, and prudential goodness is grounded in it. Having or possessing human capacities is good because it involves first actuality and being simpliciter. Developing and exercising human capacities and realizing the natural ends that correspond to them is good because it involves second actuality and qualified being. Both are good because both are modes of being, and being is convertible with goodness.

The second part of the solution is a Thomistic version of the “Aristotelian Flourishing” response. This response involves the attributive goodness (goodness of a kind) affirmed by Thomistic metaethics, specifically goodness as a human being. The Thomistic framework recognizes more kinds of goodness than just attributive goodness, because metaphysical goodness is goodness simpliciter, and it cannot be reduced to goodness of a kind. Everything that exists possesses metaphysical goodness in the same way insofar as it exemplifies the actualization of potentiality, and this kind of goodness is not wholly attributive. That being said, attributive goodness is part of the Thomistic picture. It is not the case that everything possesses being, and therefore goodness, in the same way. Goodness can be indexed to natural kinds because being can be indexed to natural kinds. The good of a thing is a function of the fulfillment of its characteristic natural powers, and different substances have different powers. Attributive goodness pertains primarily to second actuality and qualified being/perfection rather than first actuality and being/perfection simpliciter: when a thing develops and exercises (i.e., actualizes) its capacities, it gains more qualified being and therefore more goodness. The perfection of a thing is a function of its actualization or fulfillment as the kind of thing it is. Goodness as a human being is the relevant standard of human well-being because the perfection that is relevant for Thomistic perfectionism is relative to natural kinds, and humans, like other organisms, have characteristic natural capacities the actualization of which constitutes their flourishing.

Having laid out the Thomistic solution, we will offer three reasons in its favor. The first is that it is a viable answer to the Deep Problem because it supplies what the problem demands – an explanation of why nature-fulfillment is good – while avoiding Bradford's objections to the Further Theory and the Aristotelian Flourishing strategies. Her objection to the former is that

Thomistic perfectionism gets around this problem because human nature still plays a central and indispensable role in explaining the human good. The metaphysics of being and goodness serves as a further explanation of the value of nature fulfillment, but it does not replace a nature-based framework with a different one. Instead, it grounds perfectionism in a deeper and more comprehensive metaphysical theory that is itself nature based. Goodness is a matter of nature fulfillment – the actualization of species-specific potentialities – for all substances, including human beings. What is good for any living organism is the perfection of its nature, which is different for each species.

This leads into Bradford's objection to the Aristotelian Flourishing strategy. She contends that it only succeeds “in showing us an account of being good of a kind. Flourishing as a human being is just what it is to be a good instance of a human being.” But given that humans can be classified as members of various kinds, “This still leaves the deep question unanswered – why is it good to be an instance of this particular kind?” (Bradford Reference Bradford2017: 358). Thomistic perfectionism has an answer to this objection too. The question of why human nature is the relevant axiological category is answered by grounding the axiology in a more foundational metaphysics. Perfection in general is good insofar as it is the actualization of a thing's nature. A human being is human in virtue of possessing a human nature. Thus, it is good for a human being to be good qua human.Footnote ¹² In Aquinas's metaethics, it will be recalled, being and goodness can be indexed to natural kinds. Every living substance is a substance of a particular sort, which is defined by its nature. As we have seen, the goodness of a thing is determined by the actualization of its characteristic natural capacities. For human persons, human nature is the relevant metaphysical category when it comes to our second actuality and qualified perfection – the type of fulfillment and perfection that constitutes our well-being.

A second reason in favor of the Thomistic solution is that it makes for an explanatory advance in perfectionism as a theory, a version of perfectionism that is explanatorily superior to the standard versions found in the literature. The usual way of articulating the advantage of perfectionism over objective list theory is that it provides a better explanation of goodness because instead of a brute unconnected heap of goods, it offers human nature as a concept that unifies and explains the objective goods on the list. Compared to objective list theory, perfectionism has greater explanatory unity, scope, power, and depth. It unifies the list of goods by tying them all to human nature; it encompasses all the goods on the list by analyzing all of them in terms of the same thing (the development and exercise of human capacities); and it points to a more fundamental good-making property (nature fulfillment) that explains why the various goods are good. The Deep Problem, however, charges that this is not an adequate explanatory stopping point because we can ask why it is good to fulfill human nature, and standard perfectionism does not have an answer to this question.

Thomistic perfectionism is able to go this extra step and deliver an explanation that is better than standard perfectionism in the same ways that standard perfectionism is better than objective list theory. It has superior explanatory unity because it unifies all the different kinds of goodness, including goodness simpliciter, prudential goodness, and attributive goodness, by analyzing all goodness in terms of metaphysical goodness. This means that Thomistic metaethics doesn't just provide an answer to the Deep Problem for perfectionist theories of value, but also for every theory of every type of value. Relatedly, Thomistic perfectionism has superior explanatory scope because it covers all kinds of goodness whatsoever, for all of them are grounded in metaphysical goodness. It also covers all kinds of beings whatsoever, because everything is metaphysically good insofar as it has being. Finally, Thomistic perfectionism has superior explanatory power and depth in that it grounds prudential goodness in a deeper and more fundamental kind of value – metaphysical goodness – which is the foundation for all other kinds of goodness and the ultimate explanation of why every good thing is good.

In fact, Thomistic metaethics doesn't just provide a deeper explanation of the goodness of nature fulfillment, but the deepest and most ultimate explanation possible. When we consider the ontology of any given kind of thing and analyze its goodness as the actualization of potentiality, we have reached metaphysical and normative bedrock; no further explanation is possible. Since goodness is convertible with being, and since being is as fundamental as we can get, we cannot go any deeper. There cannot be any further explanation of goodness because the convertibility principle describes the ultimate foundation of reality. This is the terminus of the normative line of questioning because when we reach the level of metaphysical goodness, it is no longer sensible to ask, “Why is goodness good?”

The third reason in favor of the Thomistic solution is that Thomistic metaethics, or something very much like it, is arguably built into the perfectionist framework itself. The core perfectionist notions – ‘fulfillment’, ‘perfection’, ‘development,’ ‘exercise’, and ‘realization’ – are all “being” or “actualization” words. Take the idea that the human good consists in the fulfillment of human nature. Fulfillment is naturally understood as fullness of being; to be a fulfilled human being is to be a fully actualized human being. Consider also that perfectionism gains a significant amount of its appeal by capturing the popular intuition that a good life must be one that is fully human. To be fully human is to fully actualize one's human nature and to achieve the fullness of being that one is capable of as a rational animal. Some related ideas are wholeness and completeness. We have a desire to be whole and complete individuals, and a life that left us incomplete would not be a flourishing life. Another common intuition is that a good life involves fully realizing our human potential – we should strive to “live up to our potential” and “be all we can be.” The convertibility principle linking goodness and being seems to be part of the perfectionist package already, even if it is just an implicit background assumption. At the very least, Thomistic metaethics is a natural foundation for a perfectionist axiology.

V. Objections

One potential objection to the Thomistic solution is that it contains any metaphysics at all. It might be said that having metaphysics in an ethical theory is ipso facto a drawback, and a metaphysics-free version of perfectionism would be preferable. In response, we maintain that perfectionists cannot avoid getting metaphysical. Perfectionism, more than any other value theory, needs to appeal to metaphysics because the theory rests on a metaphysical concept: human nature. It must defend or assume substantive answers to questions such as “What kind of thing is a human being?” “Do all humans share a fixed and objective nature?” “What are the characteristic human capacities?”; and these are all metaphysical questions.

Going further, we don't think any theory of well-being can avoid metaphysics. A theory about what is good for some welfare subject S must make substantive assumptions about the kind of thing S is. Several contemporary philosophers have offered compelling arguments for the position that all theories of human well-being must assume some conception of human nature. Prinzing, for example, argues that hedonism, desire satisfactionism, and objective list theory “gain much of their intuitive plausibility by assuming perfectionist ideas … they are quite easily seen as implying claims about our nature, and objective list theorists do explicitly use perfectionism to rebut objections … [P]erfectionist intuitions are everywhere, if only implicitly” (2020: 708). For example, take John Stuart Mill's famous defense of “qualitative hedonism” over against “quantitative hedonism” (Reference Mill2001: ch. 2). In Mill's view, there are two kinds of pleasure: higher-order mental pleasures like knowledge, friendship, virtue, and art, and lower-order bodily pleasures like eating, drinking, resting, and sex. Mill contends that the former are more valuable than the latter because of their intrinsic quality, independently of their quantity. Plausibly, what is underlying and driving Mill's argument is the intuition that some pleasures are better than others because they engage the higher aspects of human nature.

A complementary line of argument is put forward by Kraut, who contends that because goodness-for is a relational concept (“G is good for S”), it ought to be grounded in facts about the nature of the good in question and the nature of the thing for which it is good: “To determine what is good for some living S, we need to know what sort of thing S is – whether it is a human being, a horse, or a tree” (Kraut Reference Kraut2007: 88). For example, to know whether coffee is good for S, one must know whether S is one's spouse or one's dog, since caffeine is beneficial to humans (especially sleep-deprived ones) but poisonous to dogs. The same goes for friendship, which is good for a human person but not good for a plant, since plants are incapable of personal relationship. Because goods and evils depend on the nature of the subject in this way, it is plausible that human well-being depends on facts about human nature. The relevant category is the human species rather than the individual or community because the fundamental good-making properties are ones that all humans possess in virtue of their common humanity, not ones specific to particular individuals or groups. As Kraut points out, this is the best and perhaps the only way to make sense of the fact that certain things are good or bad for all human beings regardless of individual makeup or group membership.

A second objection is that Thomistic metaethics is controversial. One might think that embracing Thomism saddles perfectionists with too much metaphysical baggage. Indeed, a common complaint about some Aristotelian-Thomistic versions of perfectionism is that their metaphysical framework is a liability because it is widely disputed and frequently rejected in contemporary philosophy. We have two brief replies to this objection. First, we do not attempt to defend Thomistic metaethics or address all the metaphysical objections to it in this article. Instead, we argue that it provides a solution to the Deep Problem for perfectionism, which is an important and attractive feature of the Thomistic approach. Defending the metaphysics on its own terms is a different project for elsewhere. We will simply note that there has been a resurgence of Aristotelian-Thomistic metaphysics in contemporary philosophy, and there are many notable defenders of these metaphysical doctrines (see, for example, Stump Reference Stump2003, Feser Reference Feser and Angier2019, and Oderberg Reference Oderberg2020). It is also worth noting that the rejection of Thomistic metaphysics will require a counter-metaphysics, which reinforces the point that one cannot avoid metaphysics in ethics.Footnote ¹³

Second, our approach turns the alleged liability into a benefit. In our view, the addition of a substantive metaphysical framework to perfectionism is on balance a strength rather than a weakness because it solves the Deep Problem and it increases the explanatory advantage of perfectionism over other value theories. Perfectionism's main selling point is that it offers a more satisfying explanation of goodness than competing theories. As Bradford notes, every value theory faces a “deep problem” of its own, because for every potential candidate for the ultimate good-making property (pleasure, desire satisfaction, value fulfillment, nature fulfillment, etc.), we can ask “why is that good?” So, if Thomistic metaethics gives perfectionism a successful answer to this question, and if competing value theories lack a satisfying answer of their own (as Bradford, Fletcher, and others allege), this increases the benefit of Thomistic metaphysics. In the end, we believe the advantages of Thomistic perfectionism outweigh its disadvantages.