3. The Criticism of Platonic Dualism
Another view confronting Aristotle was Plato's extreme dualism, which regarded body and soul each as a separate and complete substance. This view, which for a time Aristotle himself endorsed, was almost the exact opposite of the mechanist interpretation of life and its manifestations. If, as we have seen, it is wrong to identify the soul with the corporeal elements or with their over-all behavior, is it correct to say that the soul is a spiritual entity altogether separate from the body, on which it acts from the outside, as it were, like an extrinsic mover? St. Thomas formulates this position as follows:
Plato and his school held that the intellectual soul is not united to the body as form to matter, but only as mover to movable, for he said that the soul is in the body as a sailor in a boat. In this way the union of soul and body would only be by virtual contact (per contactum virtutis).18
Among the many arguments that make up the Aristotelian criticism and repudiation of this ultra-dualist interpretation of man, there are two that would seem to have been decisive.
First, if body and soul are each a substantial and independent unity, it is difficult to see how their association could result in a being that is truly one. As St. Thomas observes: "It follows then that a man is not one simply, and neither consequently a being simply, but accidentally." 14 Nor do you get around this dilemma by saying that the soul alone is man, the body being but an instrument that it uses. In this case man, whose whole nature would be of the spiritual order, would in no way belong to the world of physical realities, a pretension that is obviously contradicted by experience. In short, there can be no excluding the bodily side of man from the definition of man.
Secondly, if the Platonic solution is correct, how can one speak of human experiences having their source in both principles of man, that is, in body as well as soul? Yet, there are responses of this kind, as, for instance, fear, anger, and other sensations. These are not experienced in the soul alone, but involve certain definite alterations of the body as well. They point to the necessity of a true unity of being between body and soul. Furthermore, the Platonic difficulty regarding human experiences that are common to body and soul, is not explained away by saying that the soul is the active principle of such movements, which are passively received in the body. This reasoning holds for completely spiritual beings, such as angels. These can act on bodies by way of contact, but in this case the contact is merely in the order of power or action, and does not result in mover and moved becoming one in being. "Things united by contact of this kind," remarks St. Thomas, "are not one simply. For they are one in action and passion, which is not to be one simply." 15 "To act" and "to be acted on" are two distinct predicaments of accidental being; consequently, in the realm of action as in that of being, the Platonic view labors under the difficulty of its excessive dualism between the spiritual and the bodily principle of man.
To sum up, the living being bears abundant witness to possessing a real unity, notwithstanding the presence of two distinct principles, body and soul, which its behavior impels us to acknowledge. For this reason the bond between soul and body must be something more than an outer union, such as prevails between an extrinsic mover and the thing moved. These considerations led Aristotle to find and propound his own solution, which is as noteworthy as it is original.
4. The Animist (Hylomorphic) Solution of Aristotle
a) Aristotle's decisive argument leading to the definition of the soul is found in the first chapter of Book II of De Anima. His procedure consists in reviewing, one after the other, the principal categories of being. Taking as his starting point the evident fact that a living being of nature belongs to the category of corporeal being, he reasons as follows.
Substance, the first category, is either spiritual or corporeal. Corporeal substance, which is more evident to us, may be artificial or natural. Among natural corporeal substances, some have life, others not. It is the definition of living corporeal substances that we are seeking. But, in every corporeal substance, whether it is living or nonliving, three things may be considered: matter, form, and the composite. The soul of a living substance cannot be its matter, that is to say, the subject, since life is precisely a difference specifying the subject. Nor can it be the composite, which is the living body in its totality.
Since the soul is neither matter nor composite, it can be only that which specifies and determines, in other words, form. St. Thomas sums up the Aristotelian argument in the following manner: Since, then, substance may be taken in three ways, namely, as composite, matter, and form, and since the soul is neither the composite, which is the body having life, nor matter, which is the body as the subject of life, we are compelled by the logic of division to say that the soul is substance in the manner of form, being the form of a particular kind of body, namely, of a physical body having life in potency.16
In this same context St. Thomas goes on to explain why the soul is specifically the form of a body "having life in potency." The reason is that the body does not have life in act until it is informed by the soul. Next he shows that the act in question is a "first act," which means an essential form, and not merely an operative or second act. Lastly, he develops the point that the body of which the soul is the form, is a "physical, organic body." Because the soul has manifold operations for which it needs various organs as instruments, the body it informs must already have a certain organization. Putting all these elements together, we arrive at the classic definition of the soul as "the first act (or form) of a physical (natural) organic body having life in potency":
actus Primus corporis physici organici vitam in potentia habentis.17
b) In the second chapter of the same Book II, Aristotle proposes another definition of the soul, one that is based on its operations. Assuming that the soul is the first principle of life, and by life is meant self-nutrition, growth, and decay, he concludes that the soul may be defined as the principle of these activities and, in the case of man, of the higher activity of thought. So, with St. Thomas we can formulate a second, and equally classic, definition, saying that the soul is "the first principle by which we live, sense, move, and understand":
anima est primwii quo et vivimus et sentimus et movemur et intelliginius.13It will readily be seen that this definition pares down to the other, since both rest on the more general doctrine of substance. In a composite substance the first principle of all operations is the form. In other words, the form is not only the principle by which such a substance exists, "quo est," but also by which it acts, "quo operatur."
c) In brief, then, Aristotle defines the soul as the form of the body. Perhaps, by way of terminating the point, we may be permitted a word of evaluation regarding this celebrated definition. For one thing, his argument as set forth in the passages here summarized, evinces a logical structure that is altogether flawless and unassailable. But it may also, and for that very reason, seem to be somewhat abstract and remote, lacking both life and substance. Beyond that, Aristotle assumes the validity of his general theory on the nature of composite substances. If, however, we grant his doctrine of substance, everything falls into place.
Still, there is no denying that in its skeletal form, such as it appears in the first chapter of Book II, his argument, though marked, as we have said, by an inner coherence that is beyond attack, does not of itself adequately reveal the vast labor of thought actually accomplished by the Stagirite. To consider his definition as something apart, without ancestry, as it were, would be to overlook the long and careful critical analysis that makes up the entire first book, which is a major achievement in itself, representing the speculations in point of many generations of thinkers, from Empedocles to Democritus on the one hand, and from Anaxagoras to the author of the Phaedo and the Timaeus on the other. So much has gone before - Aristotle, the founder of the Lyceum, thoroughly assimilating and reliving it all in his own mind during those long years of study and reflection that went into the full development of his own doctrine. If, as Aristotle was convinced, the materialism of the ancients was unable to explain the distinctive characteristics that living things display both in their structure and activity, and if, as he was equally convinced, Platonic dualism sundered the unity of these beings to the point of no repair, clearly, then, what was needed was to find a new and more comprehensive interpretation, one that would account for all the facts at hand. Accordingly, Aristotle has recourse to the doctrine of hylomorphism, declaring the soul to be neither more nor less than the form of the body. With that, the dilemma between materialism and dualism collapses.
5. Consequences and Corollaries
a) The unity of the living being. - It was precisely his being convinced of the unity in a living thing that led Aristotle to his definition of the soul. Doubtless, a living thing is a complex entity; nevertheless, it is substantially one or unified. Moreover, the union of its substantial principles is immediate; so, there is no point in trying to explain what it is that constitutes their bond of unity, their so-called "vinculum substantiale."
Hand in hand with the unity of a living being goes the doctrine of the unicity of the soul, which means that in each such being there is but one soul. As for the special case of man, if here we speak of a vegetative soul and a sensitive soul together with the spiritual soul, this is largely just that, namely, a manner subsistent entity, with the power to perform the functions of the other two. On this point St. Thomas firmly stood his ground against all those of his contemporaries who held for a plurality, whether of souls or substantial forms.
b) The divisibility of the soul. - The unity of the soul imposes its undividedness and, it would seem, its presence as a whole in every part of the body. But here a difficulty arises. Certain vital activities, sight for example, appear to be linked to special organs. Does not this require a specification of the vital principle in regard to these organs? St. Thomas replies that it does, but only as a potential whole is specified in being a principle of diverse activities, yet remaining essentially one. Consequently, the basic indivisibility of the soul is not cornpromised.
On this matter of indivisibility the ancients experienced some perplexity because of certain phenomena observed in some living beings, such as plants and lower animals. As is well known, these can be cut or otherwise divided into separate parts that will live. Does this mean that the souls in question, which are of a less pel feet kind, have been divided? Or does it mean that new souls have been educed as if by generation? No definite answer can be given one way or another. What is important is to maintain the oneness of the soul in one living being.
c) The corruptibility of the soul. - Since it is the form of a composite substance, the soul follows the general course of such substances. Like every substantial form, it is "educed" at the moment of generation from the potency of matter; and when bodily conditions are so altered as no longer to meet the requirements of the soul, it reverts to the state of potentiality in matter from which it had been educed. The human soul, however, is directly created by God to be united to a body, and survives the destruction of the body. This is a question that has to be considered separately. From the standpoint of general biological theory the human soul must be regarded as an exception.
d) How the soul moves the body. - By explaining the living substance in terms of hylomorphism, we avoid the untenable position of materialism without undermining the unity of the living being, which is the error of Platonic dualism. But in taking this view, how can we still attribute to the soul the activity of moving the body?
The answer, in the first place, is that the soul's moving the body is not, strictly speaking, an efficient motion, that is, a movement in the order of efficient causality, because an exercise of efficient causality results jointly from body and soul, which is to say, from the living being as a whole in its composite reality. Hence, if in such a movement the soul is considered separately, it can only be as a formal principle, a principle by which or "quo." The fact is that the form exercises the role of end in regard to the activity of composite bodies, and therefore it is basically as a final cause that the soul exercises its influence on the operations of a living being. In man, accordingly, the lower activity of the sensitive and vegetative order, as well as his intellectual activity, is designed to serve the spiritual soul.