Jacques Maritain Center: Thomistic Institute

Scientific Method and the Human Soul
in Aristotle's De Anima

Steven C. Snyder, Ph.D.
Pontifical College Josephinum
Columbus, Ohio
July 15, 1998

I have included an outline of the presentation I shall give on Tuesday and an essay which I shall not read but which will be fair game as part of the discussion after my presentation. The presentation will focus on what I consider the main points of the topic, while the essay gives additional details and supplementary arguments.



I. The plan of the De anima is analogous to the plan of the Physics

II. Philosophical preliminaries

III. The primary burden of proof of the De anima is to establish the unicity of substantial form as the fundamental principle of the science of biology

IV. The argument from the De anima for the immortality of the human soul.

V. Did Aristotle believe this conclusion? Jacques Maritain's "Notes on Aristotle" appended to his Bergsonian studies.

VI. The Philosopher's perplexity as the occasion of reasonable hope for wisdom beyond reason's.




Steven C. Snyder, Ph.D.

Pontifical College Josephinum

July 15, 1998

The small mistakes in the beginning that lead to big mistakes later in modern philosophy usually come in fashioning the question itself, often in terms of a dichotomy when actually there is a third way, or even more ways, possible. This mistake has certainly taken place in modern philosophic discussions of the human soul, where the alternates seem to be either materialism or the mind-body dualism of Rene Descartes. Dualism at the cost of the unity of the human person acknowledges the unique character of intellect, making it irreducible to matter as a cause, while materialism sacrifices the uniqueness of human thought to preserve human unity. One reason this error arises among the moderns is that the human mind tends to reify, consider the objects of all of its concepts as "things;" so a distinction of mind- body or soul-body is considered a distinction of things.

Aristotle, whose philosophical insights are enlightening in so many ways, offers help here too, for his distinction between soul and body is not one of things but one of principles of a thing; the soul is the form of a living being. But then the question of human immortality arises, the problem of the survival of the soul, for if the soul is form of the body, how can it be when there is no body for it to be "of"?

Aristotle sets out to discuss the soul in general and the nature of the human soul, and its immortality, in particular in his work entitled the PERI PSYCHES, On the Soul or the De anima. A review of this work is valuable for our meeting for several reasons: the question of man's destiny after death is the most important question for us men; but also the De anima is important because of the principles of the science of biology that it establishes. For, a discussion of the human soul is really a discussion first of all of what it means to be living, and that answer is the first principle of biology. Therefore, this paper examines the fundamental principles of Aristotelian biology, and then uses those principles in a specific discussion of the human soul and human immortality. I argue that Aristotle's task in the first one-third of the De anima is to argue against reductionism or aggregationism in biology in favor of an ultimate holism which makes the biological unit, the living plant, animal, or human, the ultimate principle of explanation and intelligibility in biology. Aristotle's biological method allows, indeed necessitates, the use of modern physics and chemistry, but biological knowledge goes beyond those "sciences of the parts." This holism may be summarized by the phrase "the unicity of substantial form." Having established this point we then turn to the human person, to see whether this principle of the unicity of substantial form sheds light on the immortality of the human soul. My contention is that the De anima is the fundamental biological work of Aristotelian natural philosophy, standing to biology as the Physics stands to all of natural philosophy, and that in the De anima we find a demonstration quia per effectum of the personal immortality of each human soul. The proper biological principles of Aristotelian natural philosophy lead us to conclude necessarily that the human soul does not die with the death of the body.

This interpretation of the De anima is based on that of Thomas Aquinas, and focusses on what (Aristotelian) natural philosophy has to say on the topic of the human soul. It is another question whether Aristotle realized that was where his biology was leading him. Did Aristotle himself think the human soul is immortal? The key texts are in De anima book three, chapters four and five. But the text is corrupt and unclear as written--there is a story that applies in such instances: it is said that the texts we have are not based on Aristotle's own writings but are based on the lecture notes of a student, and a B- student at that! Yet I will follow Jacques Maritain's interpretation of that and related texts to conclude that Aristotle nowhere denies personal immortality and what he does say makes it more reasonable to say that Aristotle held for personal immortality rather than not. But Aristotle would most certainly have been perplexed with metaphysical problems of the separated soul beyond what natural philosophy can answer, or even properly raise. These problems, partly surmountable but ultimately insurmountable to even the truest natural human metaphysics, offer I suggest the grounds for a reasonable natural human hope which can serve as fitting soil for the implanting of the supernatural virtue of hope.

i. Philosophical Preliminaries

I have said that the De anima gives a demonstration quia of the immortality of the human soul; let us review briefly the Aristotelian distinction between demonstration of the fact, demonstratio quia, and demonstration of the reasoned fact, demonstratio propter quid. We only become confused if we use modern notions of inductive and deductive proof to get at how Aristotle thinks we increase our scientific knowledge of reality. The events of the world present themselves through the senses to the mind as needing an explanation, of requiring a causal explanation. Generally speaking in sciences we begin with effects and must reason to the existence of the cause. This process of reasoning to the causes is difficult and often not successful; it is one of the great accomplishments of modern science that it has developed highly effective means of finding the cause so often, and it was one of the great failings of medieval scientists that they did not understand how arduous is this task of finding the cause of a given effect. But when the cause has been discovered, when we know that this effect could only have been produced by this cause, then we have a real advance in knowledge, a scientific demonstrative knowledge, what Aristotelians call demonstration quia. In a demonstration quia we establish from what we know of the effect that its cause without doubt exists, and from a demonstration quia we know enough about the nature of the cause to know that it was adequate to produce this effect.

But of course, our minds do not rest here. We want to know the cause so well that we know precisely how the cause produces the effect. We want demonstration propter quid, in which reason moves from a knowledge of the nature of the cause sufficiently thorough to account precisely for the production of its effects. In demonstration quia, the kind of knowledge first available to our sciences of the world, our reasoning moves from effect to cause; in demonstration propter quid, the highest kind of human knowledge, our reasoning moves from cause to effect. The intellective conversion, the resolutio, of quia to propter quid demonstrations is, of course, not a matter of exchanging terms in syllogisms but of difficult and exhaustive study of the nature of the cause itself. For an invaluable historical and philosophic treatment of this process of resolutio, I refer you to the works of Fr. Wallace.

I have stated that the De anima serves a role in biology analogous to the role served by the Physics in the general science of nature. First, the Physics reasons to the principles which will be used again and again, throughout the non-mathematical scientific study of the physical world, in the demonstrations of that science. Second, the end of the Physics, Books VII-VIII, shows how these principles lead to a reality beyond the material, and so to a science beyond natural philosophy. For there Aristotle proves by a demonstration quia that there is an immaterial being or beings who is a first efficient cause of the motions of the universe. Similarly, I contend, the De anima first elucidates the fundamental principles of biology and then proves by a demonstration quia that there is an immaterial being active in the material world that does not depend for its existence on matter: the intellective human soul. In natural philosophy there are two avenues, by demonstration quia, for proving the existence of immaterial being: from the fact of a universe in motion and from the fact of man's ability to know and to love.

The investigations of Physics I-II, into the distinctions of act and potency and of substance and attribute, into the definition of nature, and into the four causes, formal, material, efficient, and final, yield the ultimate principles of demonstration for all quia and propter quid demonstrations in non-mathematical sciences of nature. However, to employ these principles the scientist must by arduous scientific investigation focus these principles specifically in individual studies. That is the nature of such principles. Second, the Physics gives a demonstration quia of the existence of an immaterial being or beings which are the ultimate source of motion in the world. We conclude that there are higher, immaterial causes upon which the material world depends; but in natural philosophy we can draw only negative conclusions about their natures: they are not material. It is left for metaphysics to demonstrate positive conclusions about the nature of these immaterial cause or causes.

Similarly, the De anima first establishes the fundamental explanatory principles of biology, general principles which must be rendered specific by detailed biological studies of genera and species of organisms. Second, the De anima, like the Physics, demonstrates the existence of immaterial being, being which does not depend on matter for its existence, the human soul. As in the Physics, so in the De anima Aristotle gives a demonstration quia that an effect we experience in the world, the human power of understanding, cannot be accounted for except by an immaterial cause of knowing, the intellective human soul. From the beginning Aristotle anticipates this conclusion and at various points in the course of the De anima Aristotle anticipates it. Let us turn to a closer examination of both these points of the De anima, the fundamental principles of biology and the argument for the immateriality and so immortality of the human soul.

ii. Biology as a Natural Science

The De anima is often referred to as a text in psychology, as the term is understood today, but in fact the De anima is properly understood as Aristotle's foundational biological treatise, in which the fundamental definition of the subject-matter of biology is determined and the principle method of biological inquiry is made manifest. This biological method rests on the general principles of the science of nature from the Physics. Living things are first of all natural beings. Biology is part of a non-mathematical science of nature, whose fundamental principles, assumed in the De anima, have been determined in the Physics.

The general principles of a science of nature are not simply given over to the biologist. Biology must adopt these principles in the special way suited to the study of living natural beings. For, "nature" is an analogical term. Nature, as determined in the Physics, is the intrinsic principle of activity and receptivity which belongs to a thing in an environment just because of the kind of thing it is. And so, as things differ in kinds, so they differ in natures. Because living things differ in kind, in "nature," from non-living things, biology is a distinct science from sciences of non-living matter, and it applies in a special way the most general principles of physical science. In other words, biology is not reducible to chemistry or physics. It is erroneous to think of a living thing as "nothing but" its elemental constituents: a living thing is more than the sum of its parts. The De anima employs principles from the Physics, but it invests those principles with the specific intelligibility proper to living beings.

This denial of reductionism is the fundamental legacy of Aristotelian biology to the modern world. But we must understand what Aristotle means, for his biological principles do allow that physics and chemistry are essential to the work of the biologist. We shall be able to investigate this point more fully after we have discussed Aristotle's definition of "soul." But before we can do that, we must discuss the notion of substantial form, for Aristotle defines the soul as the substantial form of the organic body. Aristotle's understanding of substantial form is central to his biology and so also to the Aristotelian doctrine of the immortality of the human soul. A being that is one, whose essence is expressible in a definition, has only one substantial form; all other forms belonging to it are accidental forms flowing from the unity which originates in its single substantial form. The primary grounding of the principle of the unicity of substantial form in a unified being comes in the Physics, and the most comprehensive basis for the principle is to be found in the Metaphysics.

In Physics Book One, faced with predecessors' sophisms and errors denying the reality of orderly substantial change in the world, Aristotle maintained that substantial change, which is indubitably real, is only intelligible if changeable things have a material component which in itself is purely potential, real but in no way actual. Substantial change can only be explained if matter in itself is purely potential. Existing nowhere in reality on its own, matter becomes a real principle of a thing when it is actualized by form. The primary form actualizing a composite, making matter a real principle of a thing, is called the thing's substantial form. Since matter is purely potential, the first form it receives gives being in the world to a substance, a composite of matter and form. A single substance can have only one substantial form, for where there are two substantial forms, there are two beings, two composite things. Put another way, if there were more than one substantial form in a thing, then the thing itself becomes a contradiction. If we say a triangle, for example, partakes of two substantial forms, figure and three-sided, then the one triangle both is open to more sides than three because it is figure and has exactly three sides and is denied any more because it partakes of three-sidedness. Aristotle says,

No substance is composed of substances which exist in actuality; for two objects which exist thus in actuality are never one in actuality . . . Thus, if a substance is one, it cannot consist of substances which are present in it . . . [Apostle trans., Metaphysics VII.13, 1039a4-12]

A triangle, then, realizes the perfections of a figure three-sided- ly, if one may speak in this way. Thus, according to Aristotle's natural philosophy and his metaphysics, a unified natural being can have only one substantial form, from which the perfections of the whole flow.

Of course, not everything found in nature is a single unified being; some things are aggregations of related individual things. The primary question in biology is whether living things are substantial unities or aggregates. In the De anima, Aristotle establishes as a fundamental biological principle that living things are unified organisms. Aristotle's biology rejects both mechanism and vitalism, to use modern terms. The substantial unity of living beings, and so the unicity of substantial form in living things, is the first principle determining the method of Aristotelian biological science.

iii. Soul as Substantial Form in the De anima

Aristotle's predecessors, as he makes clear in De anima Book One, erred by denying the substantial unity of living things, reducing them to aggregations of elemental components. In that first book, which is Aristotle's dialectical propaedeutic to his own determination of biology's principles, Aristotle rejects two kinds of aggregationism. The first kind identifies some particular component of the many components of a living thing as what actually lives, and this living component moves the non-living material of the whole aggregated being. Democritus, for example, posited a certain type of atom that by nature lives; a biologist today, although not one in the mainstream, might hold that it is actually individual cells which have independent life, being only incidentally related to one another in the body.

In this first kind of aggregationism, the living component need not be material stuff. Vitalism falls under this kind of aggregationism. One version of vitalism holds that the living component is life-energy, and another version holds that the living component is an immaterial soul, a substance and thing contained within and moving the body.

The second form of the aggregationist error is made by those who find life not in a particular component of the body but in the relations and interactions of all of the various individual components of the body. In this view, none of the body's material components are themselves living. Life is, as it were, a name we give to a sequence of events, the end product of a mechanically operating series. To understand life, we must understand the sequence, and nothing more.

There is some truth to this latter aggregationist view, as Aristotle recognized, and as we acknowledged earlier when we said that on Aristotelian principles physics and chemistry are essential for biology. The complexity of the bodily parts necessary for life require a multi-disciplinary approach. The error of this position according to Aristotle, however, is that it takes as the whole explanation what is only part of the explanation. In a living thing, the whole is equal to more than the sum of the parts. This view sees nothing but the sum of the parts. There would be no reality, for example to the prey-predator relationship beyond the biochemistry of each animal, according to this view. This is a conclusion Aristotle is denying. There is an organization of the whole, the substantial form, which makes sense of the organizations among the parts. Aggregationism, whether of the reductionist or the vitalist kind, is necessarily blind to the organization of the whole and focusses only on some part of the whole. This is the fundamental error Aristotle intends to reject in his fundamental biological treatise. A living thing, as evidenced by its operations, is a unified whole, not a collection or community. To be living is essential in things that live, not an accidental relation or output. There is a cohesiveness and "directiveness" in the operations of living things not to be found in non-living matter. The wholeness displayed by living things cannot be accounted for by any aggregationist theory of living things.

Aristotle's definition of soul in Book Two is a rejection of aggregationism and reductionism in biology and an assertion of the substantial unity of living things. "Soul," Aristotle says, "<is> the form of a natural body potential with life." It is the first actuality of a living body, a substantial form, not an accidental modification. Although most apparent to us are the activities of life, these activities are not the very meaning or essence of life. The distinctive operations of a living thing, nutrition, reproduction, sensation, locomotion, desire, and thinking, flow from the substantial form. These operations are caused by "parts," and by "parts" Aristotle means "powers," flowing from and dependent on the soul.

Soul, according to Aristotle's definition, is an analogical term. Defining soul is like defining a genus, which admits of specific determination, i.e., a specific way of being. There are no things simply living; things live as plants, as animals, or as humans. All the powers of life in a living being flow from a single, unified essence. Thus, the substantial unity of a living thing is preserved by the unicity of its substantial form.

Soul, then, is the actuating principle of a unified living composite being, the substantial form of a "potentially living body." The "potentially living body" of the definition does not exist in nature on its own, independent of the form of living. Inanimate bodies are not, as it were, milling about in nature's primordial soup waiting to be animated. Living bodies are substantial unities, so that to talk about a living body without life is like talking about wax with absolutely no shape at all--impossible.

And so, the soul and body, are correlates: one bespeaks the other. A soul is not a thing put into a body, it is the form of this body, so much so that we can say not only that there could not be a human soul in a rock or an aardvark or a mountain gorilla's body--that is certainly true--but also that each person's soul is uniquely suited to the body it is in and no other. A human soul cannot exist in a body different from its own, for it is the substantial form of this body. And so, a soul could not possibly preexist its body, as Plato seems to hold in the Meno. The soul comes into being with the being of the composite.

And yet we must not think that for Aristotle the body-soul unity is a unity of equals. In Aristotelian philosophy the body exists for the soul, it is not the soul that exists for the body. The soul as substantial form is the source of the being of the living composite; the matter does not contribute being to the composite. If it were to do so, then the essential unity of the whole would be destroyed, for there would be two distinct being-s in the thing, the being contributed by the soul and the being contributed by the body. Rather, for Aristotle the form is the source of the being of the living thing. Giving primacy to form is just another way, ultimately a metaphysical way, of insisting on the teleology of the biological unit as the primary intelligible of the science of biology.

Does it follow that soul, the substantial form of a living physical being, exists nowhere in reality without body? Is the corruption of the composite the corruption of the substantial form? It would seem so. But since soul is an analogical term, and since soul as form is the conveyor of being to the composite, perhaps what is true of plant and brute animal souls, that they corrupt with the composite, is not true of the human soul. We must examine the nature of the human soul.

iv. The Immortality of the Whole Individual Human Soul

According to Aristotle, we learn what something is by what it does. Aristotle establishes this principle at the outset of the Physics, when he argues that we naturally move from what we know to what we do not know, from what is more readily apparent to us to the hidden explanation of that more apparent phenomena. In the De anima the principle is expressed by saying that we reason from activities or operations, which are more apparent to us, to the underlying powers of the soul which are their source and cause, to the very nature of the soul itself, which as the substantial form is the source and cause of those powers and operations. We cannot observe our own souls (so we know Woody Allen was lying when he said he failed Metaphysics because he got caught peeking into the soul of his neighbor); we have to reason to the nature of the human soul from what we do. That is, we have to give a demonstration quia of the nature of the human soul, for the soul is the proper cause of life activities in us.

For it is the nature of the human soul, and whether it survives the death of the body, which is of ultimate interest to us in our study of the De anima. Aristotle keeps our sights right on this problem from the very 1st chapter of the work, when he says the following in De anima I.1:

. . . if there is any function or affection of the soul proper to the soul, the soul can be separated [from the body], but if no function or [affection] is proper to the soul, the soul could not be separated from the body but would be just like the straight . . . it exists always with a body. [Apostle's trans., 403a10-16]

If every human operation requires the human soul-body composite, then it is only reasonable to conclude that the soul's being does not reach beyond the soul-body composite. But if there are human operations which are independent of the body and so truly immaterial, then their source of being, the human soul, must have a being independent of the body and truly immaterial.

Now, from the discussions and arguments of De anima II.3- III.3, it is clear that the activities of nutrition, reproduction, and sensation, including the complex sensation and imagination of which the human is capable, depend on powers which are realized in healthy, functioning material bodily organs: the eye, indeed the whole complex visual system consisting of eye, nerves, and brain, are a necessary material source of the experience of seeing, for example. In plants and animals which perform operation and so exhibit powers only at the level of nutrition and sensation, we must conclude that the being of the form does not exceed the limits of the matter and that the form--the soul-- of the plant or animal comes into being and goes out of being with the composite. The soul of a dead animal is nowhere, just as the animal is really nowhere: it has gone out of existence.

In De anima III.4-5, Aristotle turns to the activity distinctive of the human soul, knowing. Knowing is the experience of being united, cognitionally, with the object known. The otherness of object and subject is broken down so that we become that which we know. The form that exists in the thing in reality comes through cognition to exist in the intellect, the NOUS. Aristotle does not go to great lengths to defend this assertion, because, as he makes clear in De anima book I, it was agreed to by his predecessors. It was the common inheritance which Aristotle could assume.

That is not the case for us today. Indeed, it is a defining principle of modern philosophy, of which Descartes is called the father, that object and idea are distinct. The modern problem, then, is to explain how we can possibly know that our ideas are like things, given modern philosophy's rejection of the cognitional identity ascribed to subject and object, knower and known, by Aristotle and his predecessors. The modern tragedy is that this epistemological task, which Descartes et al. set for themselves, is impossible to fulfill; and the scientific skepticism and ethical relativism that Thomas Aquinas explicitly stated (ST I.84.2) must follow from denying cognitional identity of subject and object indeed has followed, first among philosophers and then as a common malady of the Western world.

Aristotle and his predecessors agreed that there is an identity of knower and object known, but they disagreed on the mode of being of this identity. Aristotle's materialist predecessors thought the soul and the material things known must be made of the same material stuff. However, Aristotle argues in De anima III.4 that the knowing power must be "unmixed with the body" and "separable;" that is, NOUS is immaterial. He says,

The mind, then, since it thinks all things, must needs, in the words of Anaxagoras, be unmixed (AMIGE) with any, if it is to rule, that is, to know. For by intruding its own form it hinders and obstructs that which is alien to it ... Thus, then, the part of the soul which we call intellect (and by intellect I mean that whereby the soul thinks and conceives) is nothing at all actually before it thinks. Hence, too, we cannot reasonably conceive it mixed with the body ... the perceptive faculty is not dependent of body, whereas intellect is separable (CHORISTOS)... [Hicks trans. 429a18-25, b3-5]

Aristotle's argument for this conclusion is based on the way we know the forms of things, which is by "abstraction." A form which exists in matter in reality is conceived without matter by the intellect. In De anima III.4, Aristotle gives the example of the snub and the curved. A snub nose and indeed curves themselves have real being only in matter in the world. But the intellect abstracts the form, draws it away from the matter, investing the form with non-material being as it considers the curve of the nose apart from the material nose in which it exists. As the Posterior Analytics, especially II.19, makes clear, the intellect must have this power if science is to be possible at all. For, science must proceed from mental concepts which are necessary, universal, and unchanging; but things invested with material being are subject to change and are singular. From many material sense experiences the intellect must be able to grasp the form immaterially: "universal" is just another name for a form grasped immaterially by the intellect.

Put another way, Aristotle's argument for this conclusion is that the form as it is exists in the intellect truly is formally identical with the form as it exists in the object known. But if the intellect were material, then whatever form were received would be perceived with the qualities of the material knowing power. Just as a man wearing red glasses sees everything as red, whether they are red in reality or not, so a material intellect would invest each form thought with that material intellect's own material qualities. And thus the intellect would be incapable of knowing things as they truly are in reality.

And so Aristotle concludes in De anima III.4 that the human operation of knowing is not an operation which could be performed by or through a material organ. The operation of knowing is proper to the soul alone. Now, contemporary scholars are usually quick to point out, and quite rightly too, that Aristotle means by "unmixed and separate" only that the thinking which takes place in the intellect which becomes all things does not proceed through or depend on a material organ; he does not mean that this potential intellect is a separate substance. But this fact is obvious and indeed required by the whole structure and argument of the De anima. Thinking is an operation, and operations depend on powers of the soul. So, although Aristotle refers to NOUS, clearly what he means is the intellective power; we name the human soul by its most important power, calling it an "intellect," but properly speaking it is an "intellective soul." Indeed, it is absurd to reify NOUS, treating this power as if it were a substance distinct from the human soul which informs the body, as Thomas Aquinas points out. For if the intellect which becomes all things were a separate substance, then that separate substance would know and I, the individual man, could not be said to know. But Aristotle makes clear that it is the soul, that is, this individual man, who thinks. It is impossible on Aristotelian principles that the intellect which becomes all things be anything but a power of the individual human soul, for it is the individual human who knows.

It is important to see that the key argument of the immortality of the individual human soul has already been made, in De anima III.4. Contemporary scholars seem to give greater attention to the discussion in De anima III.5 of the intellect which makes all things, the so called "agent intellect," but already in III.4 we have what Aristotle directed his analysis towards right from the first chapter of the De anima, when he said we seek whether there is "there is any function or affection of the soul proper to the soul, <so that> the soul can be separated [from the body]". There is a function proper to the soul, arising from a power existing and acting in separation from bodily powers: the intellective power of the becoming (potentially) all things cognitionally. And so, we can follow out Aristotle's principles and argument by concluding that "the soul can be separated" from the body. The soul is a form which gives being to the body as its form but whose being is not limited to bodily existence. For, if the soul gives immaterial being to cognitional forms, then it itself must have immaterial being. If the intellective power which becomes all things has immaterial being, then that can only be because the human soul in which this power resides as a quality itself has immaterial being.

Still, there are some questions which remain, and they are occasioned by the text of De anima III.5, in which the agent intellect is first discussed.

Let us remember the principle of nature as active and receptive, for in De anima III.5 Aristotle employs this distinction analogously in the case of the intellect. He says,

But since, as in the whole of nature, to something which serves as matter for each kind (and this is potentially all the members of the kind) there corresponds something else which is the cause or agent because it makes them all, the two being related to one another as art to its material, of necessity these differences must be found also in the soul. And to the one intellect, which answers to this description because it becomes all things, corresponds the other because it makes all things, like a sort of definite quality such as light ... [Hicks trans., 430a10-15]

Prior to any sense experience the potential intellect is purely potential with respect to cognitional forms: no forms exist as actually known in it. After one has learned, as for example the scientist has, those cognitional forms may exist virtually in the intellect which becomes all things (III.4, 429b5-9), that is, not as being thought right now but easily and readily able to be thought; or the cognitional forms may exist as actually being thought right now in the intellect which becomes all things.

A second knowing power is required, an "actuating" power complementary to the "actuated" power. Where there is reception or "having been made" there must also be a maker, and so Aristotle concludes there is a corresponding power which "makes all things," later tradition's "agent intellect" or active intellective power. He compares this power to a light, and its role is to be the agent of forms' existing cognitionally in the intellect. For Aristotle, the argument for the immateriality of this power is straightforward, really as much as already made. For, if the actuated intellective power, the potential intellective power, is separate and unmixed with any bodily matter, then so much the more must the actuating intellective power, the agent intellect, exist immaterially.

The question really is not whether this agent intellect is immaterial, but rather whether this intellect which makes all things cognitionally is also a power of the individual human soul or is a separate substance which acts on the intellective power which becomes all things, causing immaterial universals in it. It is difficult to know Aristotle's view. If we employ Aristotle's own "razor," the principle of parsimony which does away with beings posited needlessly, there is no need for a separate substance which serves as an agent intellect when each soul, which already is established as having immaterial being, could more economically have accorded to it an active as well as a receptive intellective power.

Perhaps Aristotle did not definitely decide one way or the other. We remember Aristotle's doctrine, expressed earlier in the De anima, that human thought is impossible without the sense powers, especially imagination, for the senses provide to the intellect the form which it abstracts. Otherwise, the intellective power is purely potential. Also, there is this famous text in De anima III.5:

... this intellect has no intermittence in its thought. It is, however <DE>, only when separated that it is its true self, and this, its essential nature, alone is immortal and eternal. But we do not remember because this is impassive, while the intellect which can be affected is perishable and without this does not think at all. [my gloss; Hicks trans., 430a22-25]

"It alone is immortal and eternal," but what is the referent of "it." The Greek is unclear. Is it the "intellect which has no intermittence in its thought," the agent intellect, or is the referent of "it" the whole intellect, that is the human soul as having intellective powers?

In light of the previous demonstrations of the substantial unity and immateriality of the human soul, what is perishable is thought by means of bodily phantasms, what ceases to be are memories requiring bodily sensation, and the thought that is impossible is the natural thought of this life which arises from abstraction from phantasms. The whole soul survives, certainly without any possibility of exercising the nutritive and sensitive powers, but also without the power of knowing through phantasms, which are absent to the separated soul. So, the question is, do the argument and texts deny all activity of thought to the separated soul? If they do, then we must concede that our Aristotelian analysis has left us in an aporia, for a soul which cannot be said to perform any of its activities, nutritive, sensitive, or thinking, cannot be reasonably concluded to exist at all, for to live is to act according to Aristotle. But is there some way to conclude reasonably on Aristotelian grounds that the separated soul can perform the activity of thinking something?

We should note the accuracy of Thomas Aquinas' observation that we have moved beyond the subject matter of the De anima and natural philosophy with this question. The De anima gives, at least according to my contention, a demonstration quia that the immaterial soul survives the death of the body. The life and mode of existence of the separated soul is now properly part of the subject matter of metaphysics, and even if the text in De anima III.5 which we are currently discussing were clear enough that we felt reasonably sure that we understood what it said, we could only take those assertions as dialectical, since they are made without the benefit of the insight of metaphysical principles and reasoning rationally established. There is no extant Aristotelian metaphysical treatment of the separated human soul, either because it was written and it has not come down to us, as Thomas observes, or because Aristotle did not write it. Because of the importance of the question, the following brief dialectical speculation is perhaps warranted, but only if we remember that it is only dialectical, since we are going beyond the proper scientific principles of our biological investigation.

Let us speculate in turn about two possibilities, first that the active intellect of De anima III.5 is a separate substance and then that it is a proper power of each individual human soul. If the active intellect, the intellect that makes all things, is a separate substance, then the human soul after death can be assumed to continue to know some things, namely the forms infused in it by this separate active intellect. It is true that in this life our soul needs phantasms in order to think. But why? The need cannot be on the side of the intellect which becomes all things, since it is by nature open to all cognitional forms. Nor could the defect be on the side of the active intellect as separated substance, for it is the source of intelligibility. The impediment must be accidental, arising from the union of the intellective soul with the body. So, with the removal of the body, the separated agent intellect should be able to operate with greater efficacy on the soul no longer hindered by the body. What is lost by the loss of phantasms, however, is any memory of events of this world; what perishes is the natural activity of thought by means of bodily phantasms. The logic of the text in question, if the active intellect is a separate substance, is not that all thought but natural human embodied thought, through phantasms, perishes.

Suppose, on the other hand, we take the intellect which makes all things to be a power of each individual human soul. Again, the separated soul cannot know naturally without phantasms. But the separated soul is an immaterial being and a pure form, albeit one better suited to be united to the body, and so we can take the analysis of Metaphysics Lambda as giving a probable argument, and perhaps a demonstration quia per causam remotam, of the operation of the separated soul. It seems that according to Aristotle the separated soul could know itself. For, in Metaphysics XII.9, when discussing God's activity of thinking, Aristotle says,

But it appears that knowledge and sensation and opinion and thought are always of other objects, and only incidentally of themselves ... For to be thinking and to be an object of thought are not the same. Or is it not that in some cases knowledge and its object are the same? In the productive sciences, this object is the substance or the essence but without the matter, in the theoretical sciences it is the formula and the thought. Accordingly, since the intellect and object of thought are not distinct in things which have no matter, the two will be the same, and so both thought and the object of thought will be one. [Apostle trans., 1074b35-75a6]

Our argument requires only one act of knowing: the separated soul's presence to itself as an intelligible object of thought is sufficient grounds for that act. Although the agent intellect does not operate, the potential intellect does, in knowing itself (cf. De anima III.4, 430a1-5).

Thus, on Aristotelian grounds it seems there would be an operation the separated intellect is capable of performing even without phantasms, regardless of whether the agent intellect is a power of the soul or is a separated substance which infuses forms into the soul. And so, the objection that what cannot operate cannot be is irrelevant to the case of the separated human soul, which would have at least one intelligible object it knows, itself.

What was the view of Aristotle himself? Perhaps we have successfully made the argument that Aristotle's De anima can bear the weight of the quia demonstration that we have placed on it; perhaps we have established that the principles of Aristotelian natural philosophy and biology yield without contradiction demonstrative knowledge through effects that the individual human soul survives the death of the body. Still, can we say with any degree of certainty from textual evidence that Aristotle himself intended and was convinced by this demonstration? Jacques Maritain in "Notes on Aristotle" appended to his Bergsonian study argues that "one would find it difficult to say just where Aristotle declares that the NOUS is not individual", and he refers to the following texts.

Aristotle affirms the spirituality and immortality of the intellect, of the NOUS which is 'free of all corporal composition' (ALIGNS) and "separate' (CHORISTOS) (de Anima III.4, 42a11, 18),--which comes from without (THURATHEN) into the human embryo and which is 'divine' (THEION) (de Gen. Anim. II.3, 736b), --and which survives the body (HUSTERON HUPOMENEI) (Metaph.XII.3, 1070a26). <In the De anima,> Aristotle ... affirms that the possible intellect and the intellect agent are in the soul, and therefore parts of it, and calls the NOUS separate only because it has no corporal organ like the sense ... Intellect--immaterial and immortal-- is therefore personal to every man and a part (MORION) of his soul. Hence the immortality of intellect can only be the immortality of the soul itself, an evidently personal soul since it is the 'substantial form' of each individual person. [Author's emphasis, my gloss in angled brackets; pp.361-2 of the English translation by M.L. Andison. Related supporting texts cited by Maritain are 1070a26; 1026a; 1178a1-8; and 414a12-13.]

Especially noteworthy for our question are Maritain's comments on De generatione Animalium II.6, 744b22, "where Aristotle says that the NOUS that comes from without (THURATHEN), once introduced into the embryo, regulates the growth (AUKSSIS) of the tissues formed by nature (PHYSIS) ... The NOUS is therefore taken in the sense of intellective soul or of substantial form of the human organism, and it is certainly personal." That is, the intellective soul is the source of the nutritive growth of the human embryo. "In my opinion," Maritain says, "this text from the De Generatione Animalium, too little known it seems, is of first class importance in the present discussion." (p.363)

Maritain's conclusion about Aristotle's own views are reasonable and measured:

That Aristotle, as John of Saint Thomas expressed it, suffered perplexity on this question of immortality (especially because of his theory of the eternity of the world, form which it must have followed that separate souls are infinite in number, --unde valde opprimebatur), we grant without hesitation. Therefore, the principal question here is not to know whether he explicitly defined and set forth the thesis of the personal immortality of the human soul. Abiding by the exactitude of Saint Thomas's interpretation it is enough to say that, urged on by the internal logic of his principles, Aristotle (as we have already shown), taught in an implicit and virtual way,--positing the reasons which establish it,--and several times clearly hints at that immortality. (p.367)

Let us explore for a moment this Aristotelian perplexity, a perplexity inherent in natural philosophy itself. Certainly the chief cause of perplexity lay in the alpha and the omega, the origin and the ultimate dispensation, of the human soul. Lacking an explicit metaphysical doctrine of creation, Aristotle could not account for the origin of a new immaterial form, an immaterial human soul, with the beginning of each new human person. But even more disturbing, it seems to me, is what becomes of the soul after death. By nature in potency to all of being, the separated soul is fated to know less perfectly than it did in this life. Suited by nature to contemplate the divine, the separated soul is locked in contemplation of itself. Nature does nothing in vain, yet man, nature's king, is locked into an eternal frustration, a meaningless unending existence. Is absurdity the ground of the universe? For Metaphysics Lambda, certainly not; but in the case of man, it seems inescapably so. Reason cries out for consolation, but it is a consolation no natural reason can give. If God, even the God of Metaphysics XII, is the ruler of the universe, then there must be hope that there is a wisdom beyond reason that will heal the wound of the soul wrenched from its body, the intellect cut off from its Truth, and the will bereft of its Love. This is only a natural hope, the conviction that Wisdom and not insanity reigns; but could it not be fertile ground for supernatural hope?