Lesson 5: Implications of Human Knowledge

Some have supposed that because the intellect is immaterial, it cannot be the substantial form of a material body. Instead, it is related to the body as mover to moved. This position has the apparent advantage of explaining the interaction of the soul with the body without immersing it in matter. Some who find this view congenial posit a number of souls as mediators between the body and the intellect (ST, I, 76, 3). An individual human being would be alive by the vegetative soul; animal by the sensitive soul; and man by the intellectual soul. Aquinas counters that the multiplication of souls has the awkward result of rendering any particular human being only accidentally one. "Animal" would be predicated of "man" accidentally not essentially. By contrast, Aquinas recurs to Aristotle's definition of the soul as a first actuality, giving being and unity to the body. The substantial form is derived from the highest power of the soul, which contains virtually what belongs to lower souls (ST, I, 76, 4). Being contained by and ordered to the highest power in human beings, the lower powers are not the same in human beings as they are in inferior animals. They are transformed and elevated by their participation in the intellectual soul. One substantial form, the intellectual soul, gives being and unity to the whole.

The tension, which we have noted above, between soul as form and soul as subsistent is central to the opening questions of the de homine, which begins where the commentary on the De Anima concludes. Soul as form underscores our kinship with other animals, while the soul's subsistence points to our similarity to angels. Aquinas pairs an ascending, philosophical account of humans as the pinnacle of the animal kingdom with a descending, theological account of human souls as the lowest and weakest members of the genus of intellectual substances. Since we are not disembodied intellects but rational animals, the natural genus to which we belong is the genus animal. The technical terminology for what exists in its own right is hoc aliquid. Because of the argument stated above, Aquinas holds that the soul is subsistent. In response to the objection that "this particular thing" is said not of the soul but of that which is composed of soul and body, he writes:

'This particular thing' can be taken in two senses. Firstly, for anything subsistent; secondly, for that which subsists and is complete in a specific nature...Therefore as the human soul is a part of the human species, it can be called 'this particular thing' in the first sense... but not in the second sense." (ST, I, 75, 2, ad 1)

Thus, the denomination of the soul as a hoc aliquid is a qualified, analogical use of the phrase (See also Commentary on the De Anima, Bk. II, lectio 1). Aquinas proceeds to argue that the soul is not in the same species as an angel, that its mode of knowing differs markedly from that of the angel, and, finally, that the soul itself is not in any species whatsoever, since it is but part of a composite (ST, I, 75, 7).

This returns us to Aristotle's definition of the soul as the "first act of a natural, organic body potentially having life." Aristotle follows the stipulation that in the definition of a form we must state its proper subject (Commentary on the De Anima, Bk. II, lectio 1). The definition brings technical precision to the insight that the soul is the actualizing, animating, and organizing form of the body, that we cannot understand one without the other. By "first act" Aristotle distinguishes the original act which gives being and unity to a substance from its subsequent acts, which involve the operation of its proper powers. There are thus many second acts, but only one first act. Aristotle refers to the subject of the soul as an organic body; a diversity of organs is appropriate to the complexity of operations of ensouled, living beings. Since the body is receptive of the animating soul, it is described as potentially having life. As Aquinas notes it is the same thing for matter to be united to form as it is for matter to be in act. Aristotle remarks that it is as redundant to ask whether soul and body are one as it is to ask whether an act and that of which it is the act are one.

Throughout his reflections on human nature, Aquinas highlights the marvelous union of soul and body. The remarkable consequences of that union are clear from his discussions of the human body and the passions, discussions which increase our appreciation of just how complex, rich, and supple his account is. In response to the query whether God gave the human body an apt disposition (ST, I, 91, 3), Aquinas focuses upon the "upright stature" of human beings. The consequences for our relationship to the world are telling. In animals, the senses reside primarily in the face; since our face is not turned toward the ground, our senses are not confined to performing biological functions necessary for survival: pursuing food and fending off attackers. Our senses provide avenues for higher-level interaction with nature and other human beings. We are open to and receptive of the whole: "The subtlety of sight surveys the truth of all things." Our mouths do not protrude and are not primarily suited for self-defense and procuring food. If our mouths and tongues were like those of other animals, they would "hinder speech which is the proper work of reason."

It has sometimes been suggested that Western philosophical reflection about mind is wedded to an abstract and detached model of objectivity, which crystallizes in a penchant for comparing mind exclusively to sight. Aquinas's emphasis on the embodiment of reason in speech and on touch as the most human of the senses undercuts such a model. In response to the question whether the rational soul is united to an appropriate body, he highlights the importance of the sense of touch (ST, I, 76, 5). By comparison with the bodies of other animals, the human body is infirmed, that is, less immediately equipped with powers serving the maintenance of life. Instead of a "fixed" set of bodily powers, it has reason and the hand, the organ of organs, able to craft limitless tools. Moreover, the human body is ordered to activities eclipsing that of mere survival: knowledge, communication, and love. For these, it requires an "equable complexion, a mean between contraries," giving it the ability to receive and discriminate an array of sensible qualities. Such a complexion is prominent in the sense of touch, especially in the hand, which "actually grasps and takes on the form of the thing held." There is a striking analogy here between the hand's grasping of objects and the intellect's grasping of the forms of the things.

The link between touch and intelligence and the analogy between touch and thought illustrate from yet another vantage point the remarkable union of soul and body. The intellectual soul, we should recall, is the first act of the entire body, animating and informing the whole. This has important ramifications for the sub-rational powers of the human soul. For example, the participation of the lower, sensitive powers in reason is prominent in Aquinas's examination of the passions. Since the passions reside in the sensitive rather than the intellectual appetite, it might seem they could not be subject to moral appraisal. The faulty assumption here is that of an unbridgeable gap between intellect and will, on the one hand, and the sensitive appetite, on the other. Aquinas counters with Aristotle's teaching that, while the lower appetites are not intrinsically rational, they are amenable to rational persuasion and thus may participate in reason (ST, I-II, 24, 1, ad 2). Aquinas divides the passions into concupiscible and irascible. The former (which includes love and hatred, joy and sorrow) pertains to sensible good and evil absolutely, while the latter (which encompasses hope and despair, daring and fear) has a more narrow scope: the arduous or difficult good or evil (ST, I- II, 23, 1). The restricted scope of the irascible passions indicates their auxiliary and subordinate role; they are called into action when we encounter arduous goods or onerous evils. Since they concern a restricted good, they pertain to movement alone, as in struggle or flight, not to repose. Thus the concupiscible powers are prior to the irascible and, among the concupiscible, the first is love, whose inclination to the good is the cause of all the passions (ST, I-II, 25, 2). We can see here an important consequence of Aquinas's view of desire and natural inclination as ordered to appropriate ends, as fulfilled in joyful repose.

What, at this point, can we say about the union of soul and body? On the one hand, the human body is raised up, transformed by its union with the intellectual soul. On the other hand, the union with the body and its human significance means that the soul cannot sever itself from the body. We cannot disavow our bodies without courting self-misunderstanding. Leon Kass writes: "Thinking about the body is...constraining and liberating for the thinker: constraining because it shows him the limits on the power of thought to free him from embodiment, setting limits on thought understood as a tool for mastery; liberating because it therefore frees him to wonder about the irreducibly mysterious union and concretion of mind and body that we both are and live."7

Any view that treats nature and the body as "raw material for human activity and for its power" contravenes the Church's teaching on the unity of the human person, whose rational soul is per se and essentialiter the form of his body.... The person by the light of reason and the support of virtue discovers in the body the anticipatory signs, the expression and the promise of the gift of self, in conformity with the wise plan of the Creator" (Veritatis Splendor, p. 66). Aquinas's conception of the dignity of the human body and of the participation of the sensitive powers in reason underscores the mysterious unity of body and soul, what the poet John Donne's calls the "subtile knot, which makes us man."8 His poem "The Extasie," begins with a seemingly Platonic scene: two lovers lying next to one another while their souls ascend above their bodies and become one. The immateriality of the souls does not preclude their union with their bodies; in fact, that union is natural and appropriate, providing suitable vehicles for the communication of love. In Thomistic fashion, Donne proceeds to reverse the Platonic thesis of the soul trapped in the body, proposing that a disembodied soul is imprisoned. As Donne puts it,

So must pure lovers soules descend
T'affections, and to faculties,
Which sense may reach and apprehend.
Else a great Prince in prison lies.
To'our bodies turn we then, that so
Weake men on love reveal'd may looke;
Loves mysteries in soules doe grow,
But yet the body is his booke.

If the union of the intellectual soul with a body has important ramifications for the nature of the human body, it also renders the question of the ultimate destiny of the human person nearly philosophically inscrutable. This is not to say that philosophy can say nothing positive about the possibility of life beyond the grave. We have seen Aristotle provide convincing arguments on behalf of the immateriality and subsistence of the intellect. Given the natural orientation of the intellect to sensible substances and the soul to the body, whether the intellect could know anything in a separated state is problematic. In his response to that exact question (ST, I, 89, 1), Aquinas repeatedly uses the term "difficulty." He begins with the Platonic denial that the soul is the form of the body; since on this view the soul's knowledge is not assisted but impeded by the body, there is no problem with whether a separated soul can know. But it suffers a more basic difficulty; it renders the original union of soul and body inexplicable, since that union does not seem to be for the soul's good. Aristotle's position, by contrast, accounts for union but leaves us with the problem of how the separated intellect could know anything. Aquinas suggests two modes of being and knowing: one through phantasms while united to the body and another by turning directly to intelligible species when separated from the body. He adds: "To be separated from the body is not in accord with its nature, and likewise to understand without turning to phantasms is not natural to it." In fact, the knowledge of the separated soul is "general and confused" rather than "perfect and proper." How little we can complain of Aristotle's inability to resolve the issue is clear from Aquinas's statement that the separated intellect needs supernatural assistance. It knows "by means of participated species resulting from the influence of divine light." This mode of knowing is not unnatural but rather supernatural as God is the "author of the influx both of the light of grace and the light of nature" (ST, I, 89, 1, ad 3). But even this does not alter the nature of the soul in such a way that it is no longer appropriately the form of the body: "the human soul retains its proper being when separated from the body, having an aptitude and natural inclination to be united to the body" (ST, I, 76, 1, ad 6).

Reading Assignment

Summa Theologiae, I, 75-76, 80-81, 88, 89, and 90-91 

Veritatis Splendor.

Writing Assignment

1. Reflect on the distinctiveness of the human body.

2. Reflect on the difficulties surrounding the question whether the separated soul is able to know anything.

Suggested Reading

Leon Kass, "Thinking About the Body," in Toward a More Natural Science.


7. Toward a More Natural Science (New York: Free Press, 1985), p. 295.

8. "The Extasie," in The Complete Poetry and Selected Prose of John Donne (New York: Modern Library, 1952), pp. 39-41.


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