Aquinas’s Hylomorphism

Scholastic theologian and philosopher Thomas Aquinas holds that the soul is the substantial form of the body rather than a separate substance lodged within it, so that a human being is one thing and not two, and that sensation consists in receiving the form of an object without its matter—a mode of existence he calls esse intentionale, distinct from the esse naturale a form has in the object itself (Aquinas, ST I, qq. 75–76; Sentencia de anima II, lect. 24). On this framework what we would call phenomenal consciousness falls chiefly to the sensus communis, first of four interior senses, which unifies the deliverances of the external senses into a single perceptual episode and accounts for our awareness that we are sensing (Aquinas, ST I, q. 78, a. 4; Lisska, 2016). Intellectual understanding is immaterial yet must always turn toward “phantasms” supplied by sense, and the mind knows itself only indirectly, through its acts, never by direct inspection of its essence (Aquinas, ST I, q. 87, a. 1).

In other words, while Aquinas offers no theory of “phenomenal consciousness” in the modern technical sense, yet his philosophical psychology provides one of the most systematic premodern accounts of sensation, unified perceptual awareness, subjectivity, intellectual cognition, and self-awareness. On a contemporary reconstruction, phenomenal consciousness belongs primarily to the embodied sensitive life of the animal: sensory powers intentionally receive features of the world, the internal senses integrate and retain them, and affective responses give them significance; distinctively human reflective awareness then arises through an immaterial intellect that depends, during embodied life, on sensory representations or phantasms (i.e., sensory-derived mental images from which the active intellect abstracts universal concepts).

Aquinas’s importance is historical as well as conceptual: his hylomorphism offers a major alternative to both reductive materialism and later Cartesian substance dualism, while his distinction between first-order awareness and reflexive self-knowledge anticipates enduring questions concerning consciousness, embodiment, unity, and the first-person perspective (Aquinas, 1265–1274/2002; Pasnau, 2002; Cory, 2013). Thus, his relevance for contemporary consciousness studies lies less in solving any modern problem than in articulating a position that is neither dualist nor materialist, and in transmitting esse intentionale into modern philosophy as intentionality.

Embodied Phenomenal Consciousness

Aquinas’s terminology must first be translated cautiously. His conscientia ordinarily means conscience—the application of knowledge to particular acts—not what contemporary philosophy calls phenomenal consciousness (Aquinas, 1265–1274/2002, I, q. 79, a. 13). Accordingly, it would be anachronistic simply to identify a medieval faculty called “consciousness.” The closest analog of phenomenal consciousness lies instead in Aquinas’s theory of sensitive cognition: the capacity of animals, including humans, to see colors, hear sounds, feel heat and cold, taste, smell, experience bodily conditions, and undergo appetitive-affective states such as pleasure, fear, desire, anger, and sorrow.

For Aquinas, these experiences are intrinsically embodied operations. The soul is not a separate entity using the body as an instrument; it is the substantial form that makes a living body one organized animal of a certain kind. Sensory powers operate through corporeal organs, whereas cognition occurs when the sensible form of an external thing is received “intentionally”—without the perceiver literally acquiring the physical property in the same manner as the object possesses it (Aquinas, 1265–1274/2002; Lisska, 2016). Thus, seeing heat or color is not simply becoming hot or colored. Cognition involves possessing the form of another thing in a distinctive intentional mode.

This framework differs fundamentally from the early-modern picture that helped generate the modern problem of qualia. Aquinas treats colors and other proper sensibles as genuine features of external things, not merely subjective effects projected onto an intrinsically colorless world (Pasnau, 2002; Lisska, 2016). Consequently, he does not confront precisely the Cartesian-to-contemporary problem of explaining how qualitative experience could arise inside a world first characterized as devoid of qualities. But this does not amount to a solution of the modern hard problem: saying that a bodily sense receives a form intentionally does not in any sense explain why such reception has a subjective feel.

Sensation, Common Sense, and Unified Awareness

Aquinas distinguishes the five external senses from four “internal senses”: common sense (sensus communis), imagination, the estimative or—specifically in humans—cogitative power, and sensory memory. These internal powers have bodily organs and, in Aquinas’s medieval physiology, are associated with the brain. His account owes much to Avicenna and represents a sophisticated medieval attempt to explain how raw sensory inputs become a unified, temporally extended, behaviorally meaningful perceptual world (Aquinas, 1265–1274/2002; Pasnau, 2002).

The common sense is particularly relevant to consciousness studies. It integrates information across sensory modalities and enables an animal not merely to see but, in Aquinas’s formulation, to register that it sees—“when someone sees that he is seeing.” Imagination retains sensory forms after objects disappear; the estimative or cogitative power apprehends significance not reducible to surface qualities—for example, danger or usefulness—and memory preserves such contents (Aquinas, 1265–1274/2002, I, q. 78, a. 4).

It is tempting to identify the sensus communis with a modern neural “binding mechanism” or higher-order consciousness faculty, but neither identification is exact. Aquinas does not clearly distinguish phenomenal from access consciousness, nor does his common sense constitute a separate conceptual thought about a sensory state. Rather, his psychology suggests layered awareness: external sensing presents particular sensible qualities; common sense coordinates sensory activity and permits awareness of sensing; imagination, memory, and cogitation enrich the experienced world. Whether sensory consciousness should be attributed already to the external senses or especially to this integrative internal faculty remains interpretively disputed (Pasnau, 2002; Lisska, 2016).

Hylomorphism, Immaterial Intellect, and Postmortem Consciousness

Aquinas’s mind-body metaphysics resists simple classification. A human being is one substance, not a Cartesian conjunction of two independently complete substances. Soul and body are related as substantial form and matter: the intellective soul organizes the body into a living human organism and grounds its vegetative, sensory, appetitive, and rational capacities. Aquinas explicitly appeals to the unity of the subject—one and the same human being is aware of sensing and understanding—as evidence that intellect belongs to the human being rather than to some independently operating mental occupant (Aquinas, 1265–1274/2002, I, q. 76; Stump, 2003).

Yet Aquinas is obviously not a materialist. Because intellectual cognition grasps universals rather than merely particular bodily forms, he argues that intellect cannot operate through a material organ. The rational soul is consequently both the form of the body and a subsistent, incorporeal principle capable of surviving bodily death (Aquinas, 1265–1274/2002; Pasnau, 2002).

This theological commitment does not make embodiment dispensable. Aquinas regards separation from the body as an unnatural condition for a human soul. Death eliminates bodily sensation and imagination; ordinary human intellection through phantasms is therefore no longer possible. Aquinas posits a different mode of intellectual cognition for the separated soul and ultimately requires bodily resurrection for restored human completeness (Aquinas, 1265–1274/2002, I, q. 89). The result is a distinctive non-Cartesian dualism: phenomenal sensory consciousness is bodily, intellectual activity is partly immaterial, and the normal conscious human subject is the integrated body-soul organism.

The Soul as the Form of the Body

As a matter of historical importance, Aquinas's starting commitment forecloses the modern mind-body problem before it can be posed in Cartesian terms. As noted, the soul is not a thing joined to a body but the actuality of an organized living body—its substantial form, that in virtue of which this matter constitutes a living human being at all. Accordingly, there is no interaction problem, because there are not two substances to interact. The unity is so strict that Aquinas denies identifying the person with the soul: commenting on 1 Corinthians, he writes that my soul is not I, so even a surviving separated soul would not be the person.

This is of course not materialism. Aquinas argues that the intellect, unlike the senses, has no bodily organ: a material organ is receptive only to a restricted range of forms—the eye to light, the ear to sound—whereas the intellect is receptive to the forms of all material things and so cannot itself be material (Aquinas, ST I, q. 75, a. 2; Klima, 2007). The human soul is therefore subsistent, able to exist apart from the body though incomplete in that state. Whether this makes Aquinas a qualified dualist remains disputed: interpreters who emphasize the subsistence of the intellect read him as a dualist about part of the soul, while those who emphasize the form-matter unity read him as offering a third position the dualism-materialism dichotomy cannot accommodate (Pasnau, 2002; Stump, 2003).

Sensation as the Reception of Form Without Matter

The doctrine carrying most weight for phenomenal consciousness is Aquinas's account of what happens in sensing. A sense receives the form of the sensible object without its matter, and that form has a different mode of being in the sense than in the thing: natural being in the thing, intentional and spiritual being in the sense (Aquinas, Sentencia de anima II, lect. 24). Color in the wall exists as a complete quality of the wall; the same color in the medium, and then in the eye, exists incompletely—a likeness that makes the perceiver aware of the wall without making the perceiver walled.

The interpretive stakes are high and the literature divided. On a literalist reading, spiritual change involves genuine physical alteration of the organ; on a spiritualist reading, the reception is a sui generis awareness-constituting event with no separable physiological description. Burnyeat argued the spiritualist case for Aquinas (Burnyeat, 2001), having earlier concluded of Aristotle that his philosophy of mind is no longer credible, since it presupposes a physics in which matter is already pregnant with mind (Burnyeat, 1995). Sorabji argued the literalist case in reply, preserving a physiological story (Sorabji, 2001). Aquinas himself allows that touch involves natural as well as spiritual change, while vision involves spiritual change alone.

The doctrine supplies a way of describing the presence of a quality to a perceiver that neither reduces it to physical properties of the organ nor makes it a second thing alongside them. Whether this addresses the explanatory gap or declines to notice it is precisely what is contested.

The Sensus Communis and the Awareness of Sensing

Aquinas posits four interior senses: the sensus communis, the imagination, the vis cogitativa (the vis aestimativa in nonrational animals), and sense memory. The sensus communis is not a sixth sense but what he calls the common root and principle of the external senses, their common terminus (Aquinas, ST I, q. 78, a. 4). It performs two functions that map closely onto contemporary concerns.

First, it binds. The external senses each deliver their proper sensibles—color to sight, sound to hearing—and something must unify these into perception of a single object presenting several qualities at once. Aquinas assigns this integration to the sensus communis, along with discriminating the deliverances of distinct modalities as distinct. This is recognizably the binding problem, posed and assigned a faculty.

Second, and more directly, it accounts for our awareness that we are sensing. We do not merely see; we are aware of seeing, and this second-order awareness cannot belong to sight itself, whose object is color. Aquinas locates it in the sensus communis, which is why Aristotelian and scholastic writers call that faculty the seat of consciousness (Lisska, 2016). Interpreters differ on the assignment: Stump argues it is phantasia that supplies awareness of one's own mental states, while Pasnau assigns the role to the sensus communis (Stump, 2003; Pasnau, 2002).

Phantasms, Intellect, and the Turn to the Image

Above sense lies intellect, and Aquinas's account of it constrains what he can say about experience. The agent intellect abstracts intelligible species from the phantasms produced by the interior senses; the possible intellect receives them. Crucially, the intellect in this life cannot operate without turning to phantasms—the conversio ad phantasmata—so even the most abstract thought remains tethered to sensory imagery (Aquinas, ST I, q. 84, a. 7; q. 89, a. 5). The consequence is a rejection of any faculty of direct intellectual intuition of one's own states: whatever the intellect grasps, it grasps through “species” (intelligible likenesses derived from sense,) with memory and the cogitative power doing the preparatory work that makes abstraction possible.

Self-Knowledge as Indirect and Act-Mediated

Aquinas's treatment of self-knowledge speaks most directly to modern debates about introspection. The mind does not know itself through its essence; it knows itself as it knows other things, through species and through acts. We know we have a mind because we perceive ourselves understanding; we know what kind of thing a mind is only by inquiry into its acts and objects (Aquinas, ST I, q. 87, a. 1; De veritate q. 10). Powers are known through their acts, acts through their objects, so the route to self-knowledge runs outward first and only then back. This rejects the transparency of the mental long before Descartes asserted it, and it emerged partly through polemic: Aquinas developed the account against Averroes, for whom the material intellect is a single separate substance shared by all humans, arguing that the datum of individual conscious awareness—this person perceives that he himself understands—cannot be accommodated on that view (Black, 1993; Cory, 2014).

From Esse Intentionale to Intentionality

Aquinas's most traceable influence on modern consciousness studies runs through Brentano, who claimed the scholastic notion of intentional inexistence as the mark of the mental and thereby transmitted a medieval technical term into phenomenology and analytic philosophy of mind (Brentano, 1874; Sorabji, 1991). The lineage is real but has been overstated. Brentano's terminology recalls esse intentionale and intentio, yet scholars argue his construal was shaped more by Suárez and early modern representationalism than by Aquinas, and that he misread the scholastic doctrine by failing to distinguish grades of intentional existence (Perler, 2001). Others hold that for Aquinas intentionality alone was never the mark of the cognitive, since immateriality does independent work: a form exists intentionally in a medium, as color does in air, without the medium thereby being a knower. The methodological point outlasts the exegesis—a technical term survived while its theoretical setting did not, and reconstructions that read modern intentionality back into Aquinas risk describing a position no one held.

The Theological Frame: Creation, Resurrection, and the Vision of God

Aquinas's treatment of soul and cognition is not a freestanding philosophical psychology that happens to sit inside a theological work. Summa Theologiae I, qq. 75–89 falls within an account of the human being as made in the image of God, positioned between the creation of humanity and its return to its source, and several of its most philosophically load-bearing claims are shaped by commitments that are theological in origin.

The clearest case is the origin of the rational soul. Aquinas holds that God creates it directly and infuses it at the appropriate stage of generation, not transmitted by the parents and not pre-existing the body (Aquinas, ST I, q. 90, aa. 2–3). Vegetative and sensitive powers arise through natural generation; the intellectual soul cannot, because what is immaterial cannot be inferred from the potency of matter. The immateriality of the intellect and the direct divine creation of the soul are thus the same doctrine seen from two sides, and the philosophical argument for the first is doing theological work for the second.

A second case is the polemic against Averroist monopsychism. If the material intellect were a single separate substance shared by all human beings, as Averroes held, then individual immortality and individual judgment would be unintelligible—a conclusion Aquinas could not accept. But the argument he actually mounts in De unitate intellectus contra Averroistas (1270) is not from doctrine; it is from a datum of consciousness. This individual human being perceives that he himself understands. If the intellect were shared, the thinking would not be mine, and the manifest fact that I am aware of my own understanding would be false (Aquinas, 1270; Black, 1993). Theological pressure here produced an appeal to first-person evidence that is philosophically independent of the pressure that occasioned it but is doctrinally required.

The doctrine of the separated soul shows the pressure running the other way, from theology onto psychology, and with results that are complex and austere. Survival between death and resurrection requires that the soul be subsistent, and Aquinas argues that it is. But he refuses the obvious next step. The soul is not the person; the separated state is incomplete; and the natural mode of human understanding, which requires phantasms supplied by bodily organs, is unavailable to a soul without a body. The separated soul must therefore know in a different way altogether, by species infused directly by God rather than abstracted from sense (Aquinas, ST I, q. 89, aa. 1, 4, 6). Aquinas describes this state as contrary to the soul's nature, a diminished condition rather than a liberation—and this is why bodily resurrection is not an optional addendum to his anthropology but a requirement of it. A philosopher content to identify the person with an immaterial thinking substance would have had no such need.

The beatific vision marks the one systematic exception to the tethering of intellect to sense, and its structure is revealing. The ultimate end of the human being is the direct vision of the divine essence, which cannot be reached through any species abstracted from creatures and cannot be achieved by the created intellect operating according to its nature. It requires a supernatural disposition Aquinas calls the light of glory, by which the intellect is raised to a capacity it does not natively possess (Aquinas, ST I, q. 12, aa. 4–5). The consequence for the earlier doctrine is precise: the conversio ad phantasmata is a claim about the human intellect in its present embodied condition, not a claim about intellect as such.

Two further theological structures bear on how Aquinas conceives consciousness in general. Angels, as bodiless intellects, know without sensation, abstraction, or phantasms, by species infused at their creation. Aquinas thus works out in detail a model of cognition that has no sensory basis at all—the nearest premodern analog to asking whether a nonbiological intellect could think, though his answer turns on how such a being is created rather than on how it is organized. And God, by divine simplicity, is not a conscious subject among others: in God, knower, act of knowing, and object known are identical, so that divine cognition is not an instance of the kind of thing human cognition is (Aquinas, ST I, q. 14). The analogy between divine and human knowing runs in one direction only, which forecloses any move from theology to a general theory of consciousness.

The methodological upshot matters for how Aquinas is used. Contemporary hylomorphists who adopt his framework as an alternative to dualism and reductive physicalism typically drop the subsistence of the intellect—which is precisely the theologically motivated component—and retain the form-matter analysis of the living body. Whether what remains is still recognizably Aquinas's position, or a naturalized descendant that would not have satisfied him, is a live question, and one worth keeping in view when his account is enlisted in present-day debates (Pasnau, 2002; Stump, 2003).

Intellectual-Historical Importance and Contemporary Relevance

Aquinas occupies a pivotal position in the intellectual history of consciousness because he synthesizes several traditions that are often separated in modern narratives. From Aristotle he takes hylomorphism, embodied perception, and intellective abstraction; from Avicenna and the Arabic psychological tradition, a developed architecture of internal senses; from Augustine, themes concerning self-presence and self-knowledge; against Averroes, he defends the individuality of the thinking subject (Black, 1993; Cory, 2013; Pasnau, 2002).

This makes Aquinas especially important as a pre-Cartesian alternative. The familiar modern division between an objectively describable physical world and a private theater of subjective qualities is not his starting point. Sensation belongs to the organized animal as a whole, qualitative properties belong to the perceived world, bodily organs are constitutive of sensory cognition, and self-awareness emerges within cognition rather than defining mentality as such. Animals can therefore possess rich sensory awareness without rational reflection. Aquinas simultaneously preserves an irreducibly intellectual dimension of the human mind, making his theory neither physicalist nor a straightforward precursor of Cartesian dualism.

For contemporary consciousness studies, the affinities are suggestive rather than progenitive. His sensus communis invites comparison with perceptual integration; his dependence of intellect on phantasms resonates with embodied and enactive approaches; his distinction between implicit self-presence and explicit knowledge of the self anticipates modern work on pre-reflective self-consciousness; and hylomorphism offers an alternative ontology in which psychological capacities belong to organized living wholes rather than to either brains alone or detachable minds. Yet Aquinas provides no explanation of why intentional sensory processing has phenomenal character. His value for consciousness science is therefore principally conceptual and historical.

Assessment

Thus, Aquinas's importance is threefold. He supplies the most fully developed premodern account of the unity of the perceiving subject, assigning binding and the awareness of sensing to a specific faculty. He articulates a mind-body position that is neither substance dualism nor materialism, revived in contemporary hylomorphic theories offered as alternatives to both. And he is the proximate ancestor of intentionality as a term of art.

The limitations are equally clear. Aquinas has no concept of consciousness as a unified explanandum, and whether the problem of consciousness arises for him at all remains a scholarly question. Applying "phenomenal consciousness" to his position is therefore an act of translation, and convergences with contemporary theory should be treated as suggestive rather than as evidence of anticipation.

Placement

The argument is that Aquinas is the position Cartesian dualism was formulated against, and a reader who meets Descartes without him gets a truncated history. Aquinas holds that the intellect is immaterial and the soul subsistent — enough to place him in the Dualism category — while denying that the soul is the person and denying any interaction problem. That combination is exactly what Descartes abandoned, and the abandonment is more legible when the two are adjacent.

A caution, though. Placing Aquinas under Dualisms asserts something he spent considerable effort denying. He is not a substance dualist; the whole point of anima forma corporis is to refuse the dichotomy. An alternative placement in Non-Reductive Physicalism would track how contemporary hylomorphists—Jaworski, Marmodoro, Oderberg—position the view. While that placement would be more faithful to Aquinas's intent, it would be less faithful to how Landscape users will expect to find him.

References

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Sorabji, R. (2001). Aristotle on sensory processes and intentionality: A reply to Myles Burnyeat. In D. Perler (Ed.), Ancient and Medieval Theories of Intentionality (pp. 49–61). Brill.

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