Lesson 3: Aristotle's De Anima

As Aquinas notes in his commentary, the inquiry of the De Anima is pivotal in three respects (Commentary on the De Anima, Bk. I, lectio 1). First, the study of what human nature is and its proper activities is a prelude to the study of the human good in the disciplines of ethics and politics. According to Aristotle, to be a wise legislator, one must study the soul. One of the key arguments in the first book of the Ethics--the one that establishes that human happiness consists in activity of soul in accord with reason--appeals to the exercise of reason as the function peculiar to the human species. Second, metaphysics, the discipline at the pinnacle of philosophy, answers to the natural, human desire to know, an orientation which is disclosed in the study of the soul. The intellect, which is potentially all things (potens omnia), is perfected by knowing material substances and their causes. As we learn in the De Anima and as is reiterated in the opening of the Metaphysics, human beings are located at the pinnacle of the animal world, in the very middle of the cosmos. Our intellectual capacity elevates us above all other animals but the poverty of our intellect renders us inferior to the separate substances and God. Wonder is the mark of human nature, an openness to the whole. Third, in contrast to the particular sciences, which examine parts of being, metaphysics investigates being as being. Unlike physics, it is not limited to mutable beings, composed of matter and form, but ranges over all substances. The wider scope of metaphysics presupposes that non-material things exist. If only composite, material substances existed, then physics would be the fundamental and most comprehensive science. But how are we to begin to speak about immaterial things? Aquinas holds that we do so by analogy to our knowledge of the immaterial operations of our own intellects. Thus, without the knowledge, established in the De Anima, of the immateriality of the human intellect and the nature of its operation, we would not even be able to begin thinking about the nature and activity of the separate substances and God. We would not be able to study metaphysics. If the study of human nature is for Aquinas crucial to the study of philosophy, it is also central to theology. The Summa Theologiae, from which most of the material for this course is derived, is a decidedly theological text, yet in the excerpts we have included in this volume, there is virtually no argument that depends upon properly theological or revealed doctrines. Still, the guiding influence of theology is reflected in the order of proceeding. We are already familiar with the order appropriate to philosophical pedagogy, which begins from what is most evident to us and first in our experience (natural philosophy) and proceeds toward what is first in the order of nature or being (metaphysics). By beginning from God, theology reverses this order and takes as its point of departure what is first in being and last in our experience (ST, I, 2). Theology then treats the coming forth of things from God in creation and culminates in the return of all things to God through Christ and the sacraments. By far the largest segments of Aquinas's theological writings are devoted to the created order of nature, in which human nature occupies a crucial place. Before Renaissance poets called man a microcosm, Aquinas, echoing a series of venerable neo-Platonic authorities, referred to human beings as existing on the horizon of the spiritual and the material. Aquinas traces the complexity of human beings (in contrast to the simplicity of lower embodied creatures and of disembodied angels) to their being situated at the juncture of the material and the immaterial. Human beings contain the perfections of both orders (ST, I, 77, 2).

One of the advantages of beginning with Aristotle's account of nature and human nature is that we gain some familiarity with the Aristotelian vocabulary that pervades the more theological discussion in the Summa Theologiae, where he rarely pauses to explain the original context in Aristotle's own texts. Another reason is that the theological order of proceeding can mislead readers unaccustomed to Aquinas's complex pedagogical style. Since theology begins with what is prior by nature although last in our experience, the treatise on human nature begins with the soul and then turns to its union with the body (ST, I, 75-76). A reader might hastily infer from this that we could know the soul prior to, and in isolation from, the body or that we could have some sort of immediate, introspective access to the nature of the intellect. All of this is explicitly denied by Aquinas in the same treatise (ST, I, 87, 1-4), but if the differences between the philosophical and theological modes of proceeding go unnoticed, readers might come away thinking that Aquinas has more in common with Descartes than with Aristotle. Since human beings are middle creatures, they must be understood not only in relationship to what is beneath them but also to what is above them. Thus Aquinas pairs an ascending, philosophical approach that culminates with the human species as the zenith of animal life and a descending, theological approach that descends from God and the angels to man as the lowest of intellectual beings.

As creatures of open-ended wonder, human beings cannot by their own powers possess wisdom, but they can long for it and possess a portion of it. This is why Socrates calls himself a philosopher (literally a lover of wisdom) and not a sophist (one who is already wise). In modern philosophy the desire for certitude and productive power supplants the aspiration for wisdom. At the very outset of the De Anima, Aristotle notes that knowledge is desirable for two reasons: a) because of the certitude gained and b) because of the nobility of the object known. When we cannot have both, we should prefer the dim knowledge of noble objects to a certain knowledge of less dignified objects (Commentary on the De Anima, Bk. I, lectio 1).

At least for Descartes, the quest for certitude requires initially dismissing the entire order of sense and bodily experience, even my experience of myself as a body. The putting into question of the entire physical order allows the pristine intelligibility of the order of mind to come to the fore. We know ourselves better than other things and we know our intellect better than our body. The intellectual self is known immediately and transparently. Following Aristotle, and in contrast to Descartes, Aquinas urges a methodological retreat in our pursuit of self-knowledge. There is no possibility of gaining immediate, introspective access to the intellect or the soul. The route to self-knowledge is indirect, oblique. To understand the essence of any species, we must begin with the objects naturally pursued by members of the species in question, then move back from these to examine the activities, powers, and, finally, the essence. The indirect route to self-knowledge follows from the fact that the intellect is a potency made actual only by knowing things. But a power is knowable in so far as it is in act. Thus, there is no possibility of knowing the intellect until it has been actualized by knowing something other than itself.

The indirect and mediated path to knowledge of the human soul does not diminish the importance of that knowledge. Indeed, the general investigation of soul culminates with an analysis of what is proper to human souls. Thus we find Aquinas explicating in great detail Aristotle's comparison of sensation and understanding and his argument that intellect so differs from sense that it must be an immaterial power, whose operation transcends every bodily organ. Like sense, the intellect is said to be passive with respect to sensible objects. It is a potency actualized by receiving the forms of things. But there are different senses of passivity and clarification of them is crucial to a comparison of sense and intellect. Aquinas writes:

To be passive may be taken in three ways. First, in its most strict sense, when from a thing is taken something which belongs to it by virtue either of its nature, or of its proper inclination, as when ...a man becomes ill. Secondly, less strictly, a thing is said to be passive when something either suitable or unsuitable is taken away from it. And in this way not only he who is ill is said to be passive, but also he who is healed.... Thirdly, in a wide sense a thing is said to be passive, from the very fact that what is in potency to something receives that to which it was in potency without being deprived of anything. And accordingly whatever passes from potency to act may be said to be passive, even when it is perfected. And thus with us to understand is to be passive. (ST, I, 79, 2)

In its proper and first meaning, to be acted upon entails the displacement of one form by another, the destruction of the initial form by the form that emerges in the process of change. To suffer in this way is a deprivation; it involves the loss of what's proper to something, as when a man becomes ill. In a more general meaning, to suffer involves simply change of form, whether that change be suitable or unsuitable. In an even less proper sense, to suffer involves the reception of what perfects the receiver, of a form to which it is naturally in potency. Now, sensation and understanding both seem to be passivities of the last sort, the principal difference being that an excessively powerful object corrupts the sense, whereas an encounter with an inordinately intelligible object strengthens the intellect.

Wherever he discusses the immateriality of the intellect, Aquinas adduces a standard set of arguments--a) that it knows sensible things in abstraction from the here and now, that it doesn't require their actual presence to ponder them, b) that it apprehends the universal and not just the singular, e.g. not just water but what it is to be water, c) that, unlike sense, its objects are not limited to a set of contraries, that the whole of being comes under its purview, and d) that it is self-reflective; sense doesn't know or even sense that it sense, while by an act of self-appropriation the intellect is simultaneously aware of that which it knows and that it is knowing. Aquinas also spells out Aristotle's argument on behalf of the subsistence of the intellect. The conclusion follows from the coupling of the immateriality of the intellect with the premise that whatever has an operation proper to itself subsists (Commentary on the De Anima, Bk. III, lectiones 7-10 and ST, I, 75, 2).

Of course, from the vantage point of Aristotle's philosophy the separate subsistence of the intellect is troubling. Both Aquinas and Aristotle insist that, even if the intellect operates independently of bodily organs, it still needs the body to present it with an object. Here and in the Summa Theologiae, Aquinas affirms the intellect's orientation toward and dependence on phantasms for every act of knowing (ST, I, 84, 7). The intellect's transcendence of the limits of material conditions in its very act of knowing sensible substances seems simultaneously to allow for the intellect's separate existence and to undercut the possibility of its knowing anything in such a disembodied state.5 Thus does the study of soul generate seemingly insuperable philosophical difficulties. When Aquinas comes to address these issues in the Summa, he underscores their philosophical intractability (ST, I, 89, 1).6 Their satisfactory resolution can be had only from the perspective of theology, with the revealed teachings on the resurrection of the body and the graced elevation of the intellect to the vision of God. Attention to the successes and limits of Aristotle's philosophical inquiry is instructive on two points. First, it makes clear that Aquinas's preoccupation with the question of the separate existence of the intellect is not manufactured from extraneous theological concerns. Second, we see how the careful formulation of philosophical problems sets the stage for a positive engagement of philosophy by theology.

Reading Assignment

Aristotle's De Anima; Aristotle's Metaphysics, I.1.

Writing Assignment

1. Compare Aquinas's account of human self-knowledge with that of Descartes.

2. Examine carefully one or more of the arguments for the immateriality of the intellect.

Required Reading

Aristotle's De Anima: all the selections included in the Hackett volume.

See also the passages cited in these lecture notes from the Summa Theologiae (Hackett edition).

Suggested Reading

Aquinas's Commentary on Aristotle's De Anima (Dumb Ox Press).


5. See Deborah Modrak, "The Nous-Body Problem in Aristotle," Review of Metaphysics, 44 (1991), pp. 755-74.

6. See Anton Pegis, "The Separated Soul and its Nature in St. Thomas," in St. Thomas Aquinas 1274-1974: Commemorative Studies, volume I (Toronto: PIMS, 1974), pp. 131-59.


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