Target Article

Ontological Chimeras: Human Beings as Rational Animals

Back to Dignitas Issue

“What is mind? No matter. What is matter? Never mind.” After more than 33 television seasons, this remains one of my all-time favorite jokes from The Simpsons back when it was just an animated short on The Tracy Ullman Show.[1] The metaphysical view comically expressed here is that at least one aspect of a human being—the mind—is not composed of matter and, as a corollary, that matter could never compose a mind. If true, then, despite claims to the contrary,[2] the human mind is not identical with the human brain.[3] This view—typically referred to as “dualism”—can be traced back in the Western philosophical tradition to Plato and was revived in the 17th century by René Descartes.[4]

Another view, among myriad others, is the hylomorphic account formulated by Aristotle and later espoused by Thomas Aquinas.[5] “Hylomorphism” is the view that all material things are composed of two metaphysical parts: matter and form; the former is merely the potential to receive the latter. That is, a form is the principle of organization for matter such that it becomes a specific kind of thing, such as a table, a bee, a rhododendron, a cat, or a human being. This paper will articulate the Thomistic hylomorphic view of the ontological nature of human beings, arguing that we are “ontological chimeras.” That is, we are a kind of being that comprises the qualities of two different kinds of beings: a material human body and an immaterial soul/mind. Yet, unlike the Platonic or Cartesian dualist, this does not mean that each of us is composed of two distinct substances, one material and the other immaterial; rather, we are each a single unified substance composed of both a material and an immaterial part. I will then show how Aquinas’s hylomorphic view grounds an account of human flourishing and human dignity.[6] Although Aquinas is a Christian theologian, canonized saint, and doctor of the Roman Catholic Church, he is also a philosopher influenced by Aristotle and his Arabic commentators, and to a lesser extent Plato and certain Christian Neoplatonists.[7] In this paper, we will focus solely upon Aquinas’s philosophical anthropology of the human person, leaving to the side the strictly theological elements in his account of human nature, flourishing, and dignity.[8]

Thomistic Hylomorphism

According to Aquinas, a human being is essentially a person, the definition of which he adopts from the 6th-century Roman philosopher Boethius: “an individual substance of a rational nature.”[9] An example of an individual substance is President Joe Biden. As an individual substance, Joe Biden can be contrasted with humanity, which is not an individual substance but the nature in which many individual substances—including Joe Biden, King Charles III, and myself—share. Being of a rational nature—that is, having a mind capable of self-awareness,[10] abstract conceptual (i.e., intellective) thought,[11] and autonomous volition (i.e., free will)[12]—distinguishes human beings from other material substances.[13] In general, a person is a being that exists on its own with a specific nature, shared with other beings of its kind, in virtue of which it is rational. A human being is not simply a person, however. In addition to being rational, a human being is a sentient,[14] living, and corporeal substance. Human beings have a material nature.[15] Aquinas further distinguishes human beings—from other types of persons[16]—as rational animals, because, through their material bodies, human beings share certain essential qualities with other members of the animal genus.[17] The primary exemplification of such similarity is the capacity for sense-perception. A human body, though, is unique among other kinds of animal bodies in that it is organized not only to support the capacity for sense-perception, but also the capacity for self-conscious rational thought and autonomous volition. Thus, for Aquinas, the terms “human person,” “human animal,” and “human being” are extensionally equivalent.

The disposition of a human body is determined by its having a rational soul as its substantial form.[18] The term “soul” is typically understood today as a fundamentally Judeo-Christian theological concept. The concept of a soul, however, traces back to the pre-Christian Plato and Aristotle.[19] For Plato, the soul—as later with Descartes—would be equivalent to the conscious mind. For Aristotle and Aquinas, although the conscious mind is a power of the rational soul, the soul’s primary function is as the substantial form of a human body. As such, the rational soul is responsible for (1) the esse (being) of a human being, (2) the actualization of the matter composing a human being, and (3) the unity of existence and activity in a human being.[20] A rational soul and the material body it informs are not two separately existing substances. A substantial form is the actualization of a material body.[21] The intrinsic unity of a material body and a rational soul is responsible for the unified existence of a human being. A human being is not merely an aggregate of soul and body—as Aquinas understands Plato’s anthropology to hold. A rational soul and the body it informs are metaphysically distinct, but neither of them alone is a substance. A human being is the individual substance brought about through a rational soul’s informing a material body; soul and matter are thereby a human being’s metaphysical parts.[22]

Aquinas argues that a human being’s rational soul has a mode of being that distinguishes it from all other substantial forms of material substances.[23] This distinction is due to the soul’s intellectual capacities, which are not dependent upon any material body for their functioning. Hence, such capacities surpass the limits of matter in their ability to understand the universal forms of things; such universal forms are the natures of things understood as abstracted from any particular material conditions.[24] Despite the separability of its intellective operations from any material constituent, a rational soul is naturally united to a particular material body as its substantial form.[25] That a rational soul is naturally united to its body is also supported by Aquinas’s contention that it is not an intellect itself that understands, nor the soul that is the foundation for intellective capacities. Rather, a human being understands by means of the intellectual capacities she has by virtue of her soul, just as she sees by means of the capacity for sight she has by virtue of her eyes and visual cortex.[26] Hence, insofar as a human being naturally exists as composed of both soul and matter, the soul’s existence and operation is properly in union with a particular material body.

To summarize, a rational soul, while separable from its body by virtue of its essential intellectual and volitional capacities,[27] is naturally united to its body for the sake of its other capacities due to its being the body’s substantial form.[28] Because of this natural unity, a human body is disposed in terms of its organic structure with respect to a rational soul’s capacities, including the intellect.[29] Aquinas goes so far as to note that human beings have larger brains than other animals to support cognitive functions—sensation, imagination, memory, etc.—that subserve intellectual activity.[30] He even specifically notes that, if one’s brain is injured, her soul will not be able to function in terms of either intellection or self-consciousness.[31] Hence, as beings with both immaterial and material metaphysical parts, human beings can be understood as ontological chimeras.

Comparative Analysis: Substance Dualism and Reductive Materialism

Thomistic hylomorphism is often labeled as a form of dualism,[32] and it is insofar as Aquinas views a human person as having an immaterial metaphysical part. Aquinas goes so far as to argue, for philosophical and not just theological reasons, that one’s soul is capable of persisting beyond its body’s death—since the aforementioned capacities do not require a bodily organ in order to operate.[33] The soul subsequently persists in an “interim state” awaiting the resurrection of its body.[34] Thomistic hylomorphism differs from what is typically termed “substance dualism,” however, insofar as the latter view—as Aquinas receives it from Plato—holds that a human person is identical with her soul and that embodiment is an unnatural—even traumatic—state for one’s soul.[35] Aquinas explicitly rejects Platonic substance dualism and, with it, later similar versions of dualism.[36] Among the advantages of Thomistic hylomorphism over these other forms of dualism is that it affirms everything dualism does regarding (a) the irreducibility of the mind to the brain, meaning that one cannot wholly account for the mind’s nature and activity only by reference to the brain’s neural activity; (b) a strict metaphysical criterion of the individuation and persistent identity of human persons, accounting for both how each human person exists as distinct from all other persons and how each of us persists as the same person through physical and mental changes over time; and (c) the possibility of post-mortem survival. At the same time, hylomorphism avoids key problems that substance dualism faces with respect to explaining mental/physical causal interaction[37] (that is, explaining how an immaterial mind can causally influence a physical brain/body) and the phenomenological importance of embodiment[38] (that is, accounting for the fact that human persons do not perceive ourselves as having a body, as if it were a vehicle like one’s car, but rather as being embodied).

Aquinas’s view could also be labeled as a form of non-reductive materialism[39] insofar as he affirms that human beings’ natural condition is as embodied to the extent that, during the interim state between death and resurrection, Aquinas describes the soul as “longing” for reunion with its body.[40] The most prominent reductive materialist view of human nature is known as animalism: human beings are identical with a living animal of the biological species Homo sapiens.[41] The immediately apparent difference between animalism and hylomorphism is that the former view does not admit any immaterial aspects of human nature. Both views share, however, a valuing of the human body as a naturally essential component of the human person.[42] They both thereby map onto human beings’ robust phenomenological experience of their own embodiment. Thomistic hylomorphism has the advantage, however, of accounting for the ontological nature of the human mind insofar as animalism must contend with arguments against the reducibility of the mind to the brain.[43] Hylomorphism also provides a determinate metaphysical criterion—i.e., sameness of one’s soul—to account for cases of apparently overlapping animals, such as dicephalic conjoined twins.[44]

Human Flourishing and Human Dignity[45]

With this basic concept of human nature in mind, Aquinas proceeds to argue that the fundamental “good” for human beings consists in our flourishing, which is the fulfillment of our shared nature.[46] Human nature is defined by a set of capacities relative to our existence as living, sentient, social, and rational animals. Human flourishing involves actualizing these definitive capacities of the human species, such that each of us becomes the most perfect—that is, most complete or fully actualized—human being we can be.[47] To achieve this end, Aquinas claims that all human beings have a set of natural inclinations to pursue whatever we perceive to be good—that is, what is desirable to us insofar as it will help actualize our definitive capacities.[48] What he terms the “natural law” includes a set of principles that, if followed, will satisfy a human being’s natural inclinations in accord with reason and thus lead to perfection according to her nature as a human being.[49]

The Thomistic account of natural law is premised upon a relatively basic account of human nature of which the primary common features are life, sentience, sociability, and rationality. Of course, each of these features must be further defined, and such definitions, as they become more specific, may be controversial. But a high degree of specificity is not required to define certain general natural law precepts. For example, sentience may be understood broadly to refer to human beings’ capacity to sense their environment and respond to it, along with the correlative experiences of pleasure and pain. One could then deduce that depriving a person of any of her senses—say, by blinding her—or causing her unwarranted pain would be bad for her. Hence, there is an obligation to avoid intentionally or negligently depriving a person of her senses or causing her undue pain. On the positive side, restoring a blind person’s sight (should she desire it)[50] or causing a pleasurable experience would be good and thus worth pursuing.

One question that arises is whether it would be advantageous to expand a person’s visual capacity by, for example, genetically or cybernetically modifying her eyes or visual cortex such that she can perceive beyond the current visible spectrum into the infrared and ultraviolet spectra, or even utilize a novel sensory modality such as echo-location.[51] Another pertinent question is whether a person who lacks or has a diminished capacity for an essential human capacity—he is, e.g., blind, deaf, para/quadriplegic, or cognitively impaired—is an “imperfect” human being or has a lower degree, or has lost altogether, his dignity as a human person, as argued by some utilitarian bioethicists.[52]

Aquinas affirms the intrinsic dignity of human beings insofar as we are persons:

in a more special and perfect way, the particular and the individual[53] are found in the rational substances which have dominion over their own actions; and which are not only made to act, like others; but which can act of themselves; for actions belong to singulars. Therefore also the individuals of the rational nature have a special name even among other substances; and this name is “person.”[54]
“Person” signifies what is most perfect in all nature—that is, a subsistent individual of a rational nature.[55]
as famous men were represented in comedies and tragedies, the name “person” was given to signify those who held high dignity. Hence, those who held high rank in the Church came to be called “persons.” Thence by some the definition of person is given as “hypostasis distinct by reason of dignity.” And because subsistence in a rational nature is of high dignity, therefore every individual of the rational nature is called a “person.”[56]

Human beings qua persons have an essentially rational nature, the definitive capacity of which is for intellectual thought, by virtue of which human beings are self-aware and capable of understanding the universal essences of things and otherwise knowing truth that transcends material reality. Concomitant with this epistemic capacity is the capacity to appetitively orient oneself toward, or away from, what is constitutive of, or detracts from, human flourishing. Human beings have free will due to our ability to choose among various goods we may perceive and assess as appropriate means to attaining our ultimate end—i.e., flourishing in accord with our rational nature.[57] These inherent capacities, founded within human beings’ essential nature, are what grounds the inherent dignity of each individual human being as a person in possession of herself, such that she may not be considered merely as an insignificant member of a larger political whole.

Personhood is a threshold concept, meaning one either is a person or is not, versus being a matter of degree, such that severely cognitively disabled human beings might not count as persons to the same extent as cognitively more developed human beings. While any one of the traits that exemplify one’s personhood may be actualized to various degrees—autonomy, for example, is expressed in relation to various potentially coercive influences in one’s social milieu[58]—whether one has the inherent capacity for autonomy to any degree is a property one either possesses or does not. Self-awareness would be another trait that appears to be an “all or nothing” affair. I am not talking here about the extent to which one is aware of the subconscious motivators of their behavior à la Freud but being able to think substantive “I” thoughts.[59]

Human personhood also includes finitude, vulnerability, and dependency. Alasdair MacIntyre contends that there are “virtues of acknowledged dependence” that are essential for human beings to flourish.[60] Not only to survive vulnerable periods of our lives—infancy, youth, debility from age, or any temporary or permanent period of disability—but also to mature morally as practical reasoners, we are unavoidably dependent upon others. In turn, others’ vulnerability demands that we acknowledge our moral responsibility to promote their flourishing. In short, no individual person is an island unto herself with respect to her physical or moral development, and denial of human vulnerability or dependency could have a negative impact on our sense of interpersonal moral responsibility for each other’s well-being.

Finally, human personhood is inherently relational. Aristotle and Aquinas both characterize human beings as essentially social animals.[61] This thesis has been affirmed by neo-Aristotelians such as MacIntyre and Martha Nussbaum.[62] Dignity tracks, not with one or more activities or capacities, but with an ontological kind insofar as members of that kind normatively possess certain essential capacities in order to exhibit specific types of activities.


The goal of this summative excursus into Thomistic hylomorphism is to provide a cohesive portrait of the nature of human persons that challenges some of the predominant metaphysical views put forth by both classical and contemporary philosophers—such as substance dualism and reductive materialism—as well as to provide a vision of human flourishing and human dignity that not only grounds certain fundamental human rights—such as a right to health and healthcare[63]—but also counters the views of some ethicists who construe the lives of persons with various forms of disability as not to be flourishing in ways that would allow them to possess dignity, such that they may either be killed outright or at least not be allowed to come to be in the first place.[64]

What moral demands are placed upon us given the Thomistic account of human nature, flourishing, and dignity articulated in this article? First and foremost is a near-absolute requirement to respect the life of each human person, regardless of to what extent they are personally flourishing physically, intellectually, socially, or morally. I say “near-absolute” because there may be circumstances in which one may licitly perform a death-causing or death-hastening action. Such circumstances include Aquinas’s own example of killing in self-defense, which is typically taken to be the foundation for the principle of double-effect.[65] Other cases arguably include killing an enemy combatant in a “just war,”[66] administering palliative medicine which may hasten a patient’s death (usually construed as a double-effect scenario[67]), or withholding/withdrawing life-sustaining treatment if it is (a) autonomously refused by the patient or an appropriate surrogate decision-maker; (b) is disproportionate in terms of the harms/risks of continued administration in relation to the reasonably expected benefits to the patient; (c) is physiologically futile; or (d) is fairly reallocated to another patient under crisis standards of care.[68]

A second moral requirement is to provide, within the economic limits of particular societies, the material means necessary for promoting human flourishing in all of the dimensions defined above. While providing an exhaustive list would be impractical, a few illustrative examples will suffice. One example would be socioeconomic support, whether within the familial context or wider society, for single individuals or couples who are expecting a child but lack the means to properly raise their child and are thereby contemplating abortion or post-natal abandonment.[69] Another example is various forms of social support—again, from the primary social unit of the family to the various levels of political community—for persons with cognitive or physical impairments that may, lacking such social support, become disabilities that negatively impact one’s ability to flourish. To be clear, I am affirming the distinction disability scholars often draw between an “impairment,” which is a diminished degree or complete lack of a capacity to function in a way considered natural to human beings per the account described above, and a “disability,” which results from a lack of social support for persons with impairments; not every impairment entails a disability and it is arguably a social moral obligation to prevent impairments from becoming disabilities.[70]

A third—and final for the purpose of this brief article—moral requirement is to accompany persons who are approaching the end of life. As noted above, vulnerability and mortality are fundamental aspects of human nature—even given transhumanist aspirations[71]—and there are values that may be derived from the experience of encroaching debilitation and contemplating the end of one’s earthly life.[72] In order to actualize those values, however, one needs others at their side, pitying them (in the traditional sense of the term[73]) and demonstrating genuine compassion by encountering them in the context of their physical, psychological, and existential suffering. Speaking to a group of physicians, Pope Francis expresses a view of caring for those approaching the end of life that arguably can be universalized outside of a specifically Catholic moral worldview:

A doctor’s identity and commitment are not based soley on his knowledge and technical expertise, but also and above all on his merciful attitude of compassion—suffering-with—toward those who are suffering in body and in spirit. . . . True compassion marginalizes no one, it does not humiliate people, it does not exclude them, much less consider their death as a good thing. True compassion is undertaking to bear the burden. You are well aware that this would mean the triumph of selfishness, of that “throw-away culture” which rejects and scorns people who do not fulfil certain criteria of health, beauty and usefulness . . . Fragility, pain and illness are a difficult trial for everyone, even for the medical staff, they are an appeal for patience, for suffering-with; therefore we cannot give in to the functionalist temptation to apply quick and drastic solutions, stirred by false compassion or by simple criteria of efficiency and economic saving. The dignity of human life is at stake; the dignity of the medical vocation is at stake.[74]

Creating a “culture of encounter”—whether with respect to the poor, the sick, the disabled, the elderly, the dying, or simply one’s neighbor—is essential for maximizing respect for the inherent dignity of human persons, not merely in terms of avoiding violation of their negative rights not to be killed, have their freedom impinged upon, etc. but also in terms of promoting their flourishing in all of the above-specified dimensions of their being.


[1] Zappel, “The Simpsons—‘What Is the Mind?’—The Tracey Ullman Show,” YouTube, January 6, 2018,

[2] See Patricia Smith Churchland, Neurophilosophy: Toward a Unified Science of the Mind-Brain (Cambridge, MA: MIT Press, 1986); Paul M. Churchland, A Neurocomputational Perspective: The Nature of Mind and the Structure of Science (Cambridge, MA: MIT Press, 1992).

[3] We can, of course, ask similar questions about the relationship of non-human animal minds to their brains, but we will keep the focus in this paper on the human mind/brain relationship.

[4] See Plato, Phaedo; René Descartes, Meditations on First Philosophy.

[5] Note that there are different versions of hylomorphism: not only does Aquinas’s differ from Aristotle’s original formulation in certain key aspects—such as whether the human soul continues to exist after its body’s death—but there are also competing versions of hylomorphism among the Scholastics—e.g., John Duns Scotus. Furthermore, there are contemporary versions of hylomorphism that are not explicitly Thomistic; see William Jaworski, Structure and the Metaphysics of Mind: How Hylomorphism Solves the Mind-Body Problem (New York: Oxford University Press, 2016).

[6] For a more in-depth comparative analysis, see Jason T. Eberl, The Nature of Human Persons: Metaphysics and Bioethics (Notre Dame, IN: University of Notre Dame Press, 2020), from which some of the material in this article is derived.

[7] For a concise, summative history of the reintroduction of Aristotle’s works to the Latin West through Arabic commentaries, see Richard E. Rubenstein, Aristotle’s Children: How Christians, Muslims, and Jews Rediscovered Ancient Wisdom and Illuminated the Dark Ages (New York: Harcourt, 2003). For the influence of Aristotle and his Arabic commentators on Aquinas’s thought, see Jean-Pierre Torrell, Saint Thomas Aquinas, Vol. 1: The Person and His Work, trans. Robert Royal (Washington, DC: Catholic University of America Press, 2005).

[8] Though I mention pertinent theological elements in the footnotes for the sake of a more complete and accurate presentation of Aquinas’s anthropology.

[9] Thomas Aquinas, Summa theologiae [ST], trans. English Dominican Fathers (New York: Benziger, 1948), 1.29.1; cf. Boethius, Contra Eutychen et Nestorium, in Theological Tractates, trans. H. F. Stewart, E. K. Rand, and S. J. Tester (Cambridge, MA: Harvard University Press, 1973), III. Interestingly, Boethius developed this definition to help him rationally explain the two natures of the one divine person, Christ. Despite being theologically motivated, the Boethian formula serves as a defensible philosophical definition of a “person.”

[10] See Aquinas, Summa contra Gentiles [SCG], 2.49; In Sent, II, d. 19, q. 1., a. 1; In Librum de causis expositio, prop. XV; John Haldane, “(I Am) Thinking,” Ratio 16, no. 2: (2003): 124–39,

[11] See ST, 1.79.

[12] See ST, 1.83.

[13] See Aquinas, Quaestio disputata de anima [QDA], q. un., a. 3.

[14] The term “sentient” is often used in contemporary discussions to refer to whatever mental capacity, or set of capacities, that distinguishes persons from non-persons. The root of this term, however, is the Latin word sentire, which means “to feel”; it thus more properly refers to the capacity for consciousness of what one senses. Hence, all animal species, endowed with the capacity for sense-perception in various forms and concomitant conscious awareness of the objects they perceive, count as sentient. For Aquinas, mere consciousness of what one senses is not what distinguishes persons from non-persons, but rather the capacity for self-conscious rational thought and autonomous volition.

[15] See Aquinas, Expositio super librum Boethii De trinitate, q. 5, a. 3.

[16] Aquinas recognizes different types of beings as persons. In addition to human beings, Aquinas claims that angels are persons who exist as pure immaterial intellects, and that God exists as three distinct persons; see ST, 1.29–30.

[17] See Aquinas, Sententia super Metaphysicam, bk. VII, lect. 3, §1326.

[18] Following Aristotle, Aquinas defines a “rational soul” as a soul that has the relevant capacities for life, sensation, locomotion, self-conscious rational thought, and autonomous volition, and as the type of soul proper to the human species. A “sensitive soul” possesses the relevant capacities for only life, sensation, and—for some species—locomotion, and is the type of soul proper to all non-human species of the animal genus. A “vegetative soul” has the relevant capacities for life alone and is proper to all non-animal living organisms. See Aristotle, De anima, bk. II, ch. 3, 414a30–415a14.

[19] For a concise, summative history of the concept of “soul,” see Raymond Martin and John Barresi, The Rise and Fall of Soul and Self: An Intellectual History of Personal Identity (New York: Columbia University Press, 2008).

[20] See SCG, 2.68; Sententia libri De anima [In DA], bk. II, lect. 2.

[21] See SCG, 2.69.

[22] See ST, 1.75.4. Referring to a human being’s soul and the matter it informs as parts requires an extended notion of “part” than the standard conception of parts as integral to a substance, in the way a roof, walls, and floor are parts of a house. Such parts are composites of matter and form that exist even when they do not compose something else. Soul and matter, on the other hand, can be understood as metaphysical parts that do not exist individually without composing a human being. For more on this distinction, see Eleonore Stump, Aquinas (New York: Routledge, 2003), 42, 209–10; Aquinas, Scriptum super libros Sententiarum [In Sent], bk. II, dist. 3, q. 1, a. 4.

[23] See In Sent, bk. I, dist. 8, q. 5, a. 2 ad 1.

[24] See ST, 1.75.5.

[25] See QDA, q. un., a. 3 ad 16; ST, 1.76.

[26] See SCG, 2.76.

[27] Aquinas does not provide extensive arguments connecting a rational soul’s volitional capacity with its immateriality. Yet, he does consider a separated soul to be capable of volition and also grounds the will’s autonomy in the soul’s ability to intellectually cognize and deliberate about the various “goods” that it may elect to pursue; see ST, 1.83.

[28] See In DA, bk. II, lect. 2; SCG, 2.68; ST, 1.76.1.

[29] See QDA, q. un., a. 8 ad 15, a. 10, ad 1-2; In DA, bk. II, lects. 1, 19; ST,, 1.91.3.

[30] See QDA, q. un., a. 8.

[31] See Aquinas, Quaestio disputata de spiritualibus creaturis, q. un, a. 2 ad 7.

[32] See J. P. Moreland and Scott B. Rae, Body and Soul: Human Nature and the Crisis in Ethics (Downers Grove, IL: InterVarsity Press, 2000); Eleonore Stump, “Non-Cartesian Substance Dualism and Materialism without Reductionism,” Faith and Philosophy 12, no. 4 (1995): 505–31,; Brian Leftow, “Souls Dipped in Dust” in Soul, Body and Survival: Essays on the Metaphysics of Human Persons, ed. Kevin J. Corcoran (Ithaca, NY: Cornell University Press, 2001), 120–38.

[33] As noted above, the operation of these capacities does require certain conditions of embodiment when the soul is informing its body—i.e., the body must provide the intellect with content for it to abstract conceptual data from via sense-perception. Hence, neurological damage can hinder the soul’s ability to operate intellectively even though the root capacity to think intellectively remains. See Jason T. Eberl, “Extraordinary Care and the Spiritual Goal of Life,” National Catholic Bioethics Quarterly 5, no. 3 (2005): 491–501,

[34] See Eberl, The Nature of Human Persons, ch. 7. With respect to bodily resurrection, although Aquinas understands the event to require divine intervention, he also provides a philosophical justification for it based on the soul’s natural “longing” for reunion with its body and the Aristotelian principle that “nothing that is against nature can be lasting”; see Aquinas, Compendium theologiae, ch. 151 and SCG, 4.79.

[35] See Plato, Meno.

[36] See Eberl, The Nature of Human Persons, ch. 3. There is some reason to interpret Descartes as holding a view more akin to hylomorphism than substance dualism; see Justin Skirry, “A Hylomorphic Interpretation of Descartes’s Theory of Mind-Body Union,” Proceedings of the American Catholic Philosophical Association 75 (2001): 267–83,

[37] See Jaworsk, Structure and the Metaphysics of Mind; James D. Madden, Mind, Matter, and Nature: A Thomistic Proposal for the Philosophy of Mind (Washington, DC: Catholic University of America Press, 2013).

[38] See Maurice Merleau-Ponty, Phenomenology of Perception, trans. Colin Smith (New York: Routledge, 1962).

[39] See Stump, “Non-Cartesian Substance Dualism and Materialism without Reductionism.”

[40] See QDA, q. un., a. 8.

[41] See Eric T. Olson, The Human Animal: Personal Identity Without Psychology (New York: Oxford University Press, 1997); Paul F. Snowdon, Persons, Animals, Ourselves (New York: Oxford University Press, 2014); Stephan Blatti and Paul F. Snowdon, eds., Animalism: New Essays on Persons, Animals, and Identity (New York: Oxford University Press, 2016).

[42] The term “naturally” is included insofar as Thomistic hylomorphism allows for the unnatural existence of a human person as composed of their disembodied soul alone; for animalists, the body is unqualifiedly essential for a human person to exist. For an account of how a human animal could persist without a material body, see Allison Krile Thornton, “Disembodied Animals,” American Philosophical Quarterly 56, no. 2 (2019): 203–17,

[43] See Richard Swinburne, The Evolution of the Soul, rev. ed. (New York: Oxford University Press, 1997); William Hasker, The Emergent Self (Ithaca, NY: Cornell University Press, 1999); Robert C. Koons and George Bealer, eds., The Waning of Materialism (New York: Oxford University Press, 2010).

[44] See Tim Campbell and Jeff McMahan, “Animalism and the Varieties of Conjoined Twinning,” Theoretical Medicine and Bioethics 31, no. 4 (2010): 285–301, For a hylomorphic response, see Eberl, The Nature of Human Persons, 54–58.

[45] Material in this section is derived from Jason T. Eberl, “A Thomistic Appraisal of Human Enhancement Technologies,” Theoretical Medicine and Bioethics 35, no. 4 (2014): 289–310,; Eberl, “The Ontological and Moral Significance of Persons,” Scientia et Fides 5, no. 2 (2017): 217–36,

[46] ST, 1–2.18.5, 1–2.49.2, 1–2.71.1.

[47] ST,

[48] ST, 1.5.1.

[49] ST, 1–2.94.2.

[50] Note that one need not desire something in order for it to be a good. Sight could be a good in accord with human nature and flourishing even if one does not actually desire it. Whether one has a desire for sight, however, could make a difference as to whether it would be appropriate to take action to restore one’s sight. There is a growing body of literature from a Thomistic perspective on disability; see citations in n. 70 below. I thank an anonymous reviewer for raising this question.

[51] For discussion of human enhancement from a Thomistic perspective, see Eberl, “A Thomistic Appraisal of Human Enhancement Technologies,” 2014.

[52] See Helga Kuhse and Peter Singer, Should the Baby Live? The Problem of Handicapped Infants (New York: Oxford University Press, 1985); Alberto Giubilini and Francesca Minerva, “After-Birth Abortion: Why Should the Baby Live?” Journal of Medical Ethics 39, no. 5 (2013): 261–63,

[53] Aquinas is referencing here the Greek term hypostasis (Latin: suppositum).

[54] ST, 1.29.1. Aquinas also grounds human dignity theologically insofar as we are created in the “image and likeness of God” (imago Dei); see Aquinas, Quaestiones disputatae de veritate, q. 25, a. 6 ad 2; ST, 1.93.

[55] ST, 1.29.3.

[56] ST,

[57] Human beings also have a supernatural end—i.e., loving union with God; see ST, 1–2.1–5.

[58] See Tom L. Beauchamp and James F. Childress, eds., Principles of Biomedical Ethics, 7th ed. (New York: Oxford University Press, 2013), 105.

[59] See Lynne Rudder Baker, Naturalism and the First-Person Perspective (New York: Oxford University Press, 2013).

[60] See Alasdair MacIntyre, Dependent Rational Animals: Why Human Beings Need the Virtues (Chicago, IL: Open Court, 1999).

[61] See Aristotle, Nicomachean Ethics, 1.7.1097b9, 9.9.1169b16, 10.8.1178b5; Aquinas, Sententia libri Ethicorum, bk. I, lect. 9.

[62] See MacIntyre, Dependent Rational Animals; Martha C. Nussbaum, “Human Functioning and Social Justice: In Defense of Aristotelian Essentialism,” Political Theory 20, no. 2 (1992): 202–46,

[63] See Jason T. Eberl, Eleanor K. Kinney, and Matthew J. Williams, “Foundation for a Natural Right to Health Care,” Journal of Medicine and Philosophy 36, no. 6 (2011): 537–57,

[64] Kuhse and Singer, Should the Baby Live? Julian Savulescu, “Procreative Beneficence: Why We Should Select the Best Children,” Bioethics 15, no. 5–6 (2001): 413–26,

[65] ST, 2-2.64.7; Joseph Mangan, “An Historical Analysis of the Principle of Double Effect,” Theological Studies 10, no. 1 (1949): 41–61,; Joseph Boyle, “Toward Understanding the Principle of Double Effect” Ethics 90 (1980): 527–38,; P. A. Woodward, ed., The Doctrine of Double Effect: Philosophers Debate a Controversial Principle (Notre Dame, IN: University of Notre Dame Press, 2001); T. A. Cavanaugh, Double-Effect Reasoning: Doing Good and Avoiding Evil (New York: Oxford University Press, 2006); Lawrence Masek, Intention, Character, and Double Effect (Notre Dame, IN: University of Notre Dame Press, 2018).

[66] See ST, 2–2.40; John Langan, “The Elements of St. Augustine’s Just War Theory,” Journal of Religious Ethics 12, no. 1 (1984): 19–38,; Michael Walzer, Just and Unjust Wars: A Moral Argument with Historical Illustrations (New York: Basic Books, 2015); Jeff McMahan, Killing in Wars (New York: Oxford University Press, 2011).

[67] See Jason T. Eberl, “Aquinas on Euthanasia, Suffering, and Palliative Care,” National Catholic Bioethics Quarterly 3, no. 2 (2003): 331–54,

[68] See Jason T. Eberl, Thomistic Principles and Bioethics (New York: Routledge, 2006), ch. 5; Michael J. Redinger and Jason T. Eberl, “New Developments in End-of-Life Teaching for Roman Catholic Healthcare: The Implications of Samaritanus Bonus (‘The Good Samaritan’),” American Journal of Hospice and Palliative Medicine 39, no. 5 (2021): 501–3,; Jason T. Eberl, “Unilateral Withdrawal of Life-Sustaining Treatment within Crisis Standards of Care,” Health Care Ethics USA 29, no. 1 (2021): 8–10,

[69] See Jason T. Eberl, “Cultivating the Virtue of Acknowledged Responsibility,” Proceedings of the American Catholic Philosophical Association 82 (2008): 249–61,

[70] See Bryan R. Cross, “A Thomistic, Non-Ableist Conception of Impairment and Disability,” National Catholic Bioethics Quarterly 20, no. 2 (2020): 233-42,; Jason T. Eberl, “Disability, Enhancement, and Flourishing,” Journal of Medicine and Philosophy 47, no. 5 (2022): 597–611,

[71] See Mark Coeckelbergh, “Vulnerable Cyborgs: Learning to Live with Our Dragons,” Journal of Evolution and Technology 22, no. 11 (2011): 1–9,; Belén Liedo Fernández and Jon Rueda, “In Defense of Posthuman Vulnerability,” Scientia et Fides 9, no. 1 (2021): 215–39,

[72] See Jason T. Eberl, “Religious and Secular Perspectives on the Value of Suffering,” National Catholic Bioethics Quarterly 12, no. 2 (2012): 251–61,

[73] Harold Braswell, “Take Pity: What Disability Rights Can Learn from Religious Charity,” Journal of Medicine and Philosophy 47, no. 5 (2022): 638–52,

[74] Pope Francis, “Address to Directors of the Orders of Physicians of Spain and Latin America,”, June 9, 2016,