On the Soul by Aristotle

First transcribed:De anima, second Athenian period, 335-323 b.c.e. (English translation, 1812)

Type of Philosophy: Metaphysics, philosophical psychology

Context

On the Soul is divided into three books. The first consists mainly of a review of the opinions of Aristotle’s predecessors about the soul, and refutation of their errors. The second book and the first part of the third define the soul and describe and explain the nutritive and sensitive faculties. The rest of the third book treats the intellect.

The original meaning of the word psychē was “breath,” and in the earliest Greek literature it had come to stand for “breath-soul,” being identified with vital functions in general, while a separate blood-soul was held to be the seat of consciousness. Aristotle seems to have been unaware of this view. By his time, psychē meant “life-principle,” whether simple or complex, the inner cause of vital movements of all kinds.

Theories of the Soul

Aristotle begins by describing in detail the views about the soul held by his predecessors, finding them to fall into two groups: first, those according to which the soul is one of the elements (earth, air, fire, water) or some combination of them, or a special (material) soul-substance, and second, the doctrine that the soul is the harmony of the body. Theories of the first kind have in common the characteristic of trying to account for bodily movements by postulating a power of self-movement in the soul. Aristotle says they are mistaken, for the soul cannot have any motion at all. The theories require it to have a natural motion, and if it had, it would (by Aristotle’s doctrine of motion) have a natural place toward which it moved, a condition manifestly impossible. Aristotle treats the harmony theory very literally and unsympathetically. He interprets it as meaning that the soul is the ratio of the elements that go to make up the body, and he points out that because, for example, the ratio of elements in bone is different from that in flesh, there would have to be as many souls in one body as there are different kinds of tissues.

It is curious that Aristotle does not discuss the immortality of the soul. As is well known, belief in personal immortality was not widely held in Greece; however, Plato and some of his Pythagorean predecessors had taught transmigration. Aristotle declares almost at the outset that he is not inclined to think that the soul can exist separate from its bodily substratum—though he makes an exception for the intellect, which he says “seems to be an independent substance implanted within the soul and to be incapable of being destroyed.” To the familiar argument that mental powers are observed to decline along with bodily ones, he replies that senility is not a defect of the mind as such, but a progressive incapability of the body to use the mind aright. This exception does not constitute an endorsement of belief in personal immortality, for thinking is impersonal. The arguments of Plato are not even mentioned.

Actuality and Potentiality

In book 2, Aristotle defines the soul as the “first grade of actuality of a natural body having life potentially in it.” It is “the essential whatness’ of a body.” It is not really possible to understand these definitions without prior acquaintance with the whole of Aristotle’s physics and metaphysics; but it is hoped that the following explanation suggested by Aristotle’s discussion of causes will be of some help.

There are four questions that can be raised about a couch. (1) What is it made of (what is its material cause)? (2) What sort of thing is it (what is its formal cause)? (3) How was it made (what was its efficient cause)? (4) What is its purpose (what is its end or final cause)? When all these questions are satisfactorily answered, then (and only then) is it possible to understand the couch. So, in general, artificial objects are produced when someone takes raw materials and by moving them imposes a form on them for a certain purpose. The process of making a couch is to be looked upon as a movement from the potential to the actual. A heap of cloth, springs, and wood is potentially a couch; the maker’s activity moves these ingredients from the state of potentiality to that of being actually a couch. These terms, however, are only relative; what is potentially a couch (the matter of a couch) is at the same time actually cloth, springs, and wood.

The world consists of particular things. Those that are not artificial are natural, and the significant difference between natural and artificial things is that while the latter have their form imposed on them from outside, the former have their own internal principles of motion (in the broadest sense, including growth). Hence everything is to be understood in the way a couch is understood: as a particular thing, a this, consisting of a certain matter that takes on a certain form or whatness—that is, it undergoes a process of development from a condition of potentiality to a state of actuality. It is possible to understand an acorn when one knows that it is a potential oak tree, that it is the sort of thing that has the internal power of developing (organizing itself and other matter) into (not just anything but specifically) an oak tree.

Articles of furniture are classified according to their shapes. The whatness of a table is distinguished from the whatness of a chair by mere outline. However, even in this instance, the difference in form amounts to a difference in function. What makes a thing a knife is not its shape but its ability to cut: The form of whatness of a knife is cutting. It is in an analogous sense that Aristotle declares the soul to be the essential whatness of a living body.

A bar of unsharpened steel is potentially a knife. When it is shaped and sharpened, it is actually a knife. However, the word “actually” is ambiguous. The object is actually a knife both when it is actually cutting something and also when it is resting in a scabbard, in a condition to cut. The actuality of the knife in the scabbard Aristotle calls the “first grade of actuality” to distinguish it from the second grade, manifested only when the knife is cutting. Therefore, for the first definition of soul, the soul is not an ingredient of a body or an extra organ; it is the organization and functioning of the body. If a body has life potentially in it, the soul is the actuality (developed potentiality) of life. It is the “first grade” of actuality because not all the vital functions are in exercise at every moment. Hence, the immortality of the soul is out of the question. Further, it is as meaningless to ask whether soul and body are one as to wonder whether a piece of wax and its shape are one or two. It is not wrong to say that the animal is its body plus its soul, if care is taken to realize that this is to be interpreted in the same sense as the statement that the pupil plus the power of sight constitute the eye. (It appears that Aristotle’s own doctrine was not so far as he thought from the harmony-of-the-body theory.)

The Soul and Life

The soul is the life-principle. However, what is it to live? It may mean “thinking or perception or local movement and rest, or movement in the sense of nutrition, decay and growth.” Plants have the power of nourishing and reproducing themselves, as do all living things, “in order that, as far as their nature allows, they may partake in the eternal and divine. That is the goal toward which all things strive, that for the sake of which they do whatsoever their nature renders possible.” Animals have in addition the faculty of moving from place to place, and sensation that makes movement feasible; all animals have at least the primary sense of touch and taste, which is a kind of touch. Only humans are endowed with the power of thought, which “is capable of existence in isolation from all other psychic powers.” However, although Aristotle distinguishes thus radically between thinking and the other psychic powers of reproduction, nourishment, and sensation, it is probably a mistake to attribute to him the doctrine that humanity has three (separate or separable) souls.

In all senses of cause except material cause, the soul is the cause of the body. It is the body’s source or origin of movement (efficient cause), the essence of the whole living body (formal cause), and the purpose for which the body exists (final cause).

The Senses

The remainder of book 2 treats of the faculty of sensation and of the five senses. “By a sense’ is meant what has the power of receiving into itself the sensible forms of things without the matter,” as the wax receives the imprint of the seal. (“Sensible form” seems to mean any form that can be perceived. Thus, shapes are sensible forms, souls are not.) The process of sensing is this: The sense organ consists of two or more of the four elements in a certain ratio, the combination being such as to be suitable matter for receiving a certain range of sensible forms. When I see a hippopotamus, there is no hippopotamus (natural body, matter and form) in my eye. What is there is the matter of the eye, which has now taken on the sensible form of the hippopotamus and is in consequence qualitatively identical with the hippopotamus. I cannot see sounds or hear colors because the matter of the eye is such as to be the potentiality only of colors, the ear only of sounds. The power of the sense organ to perceive, then, is the ratio of the elements in its composition.

On sight, Aristotle says, “What is visible is color and color is what lies upon what is in its own nature visible.” In order that something may be seen, there must exist a colored object, a transparent medium, and light. They are related as follows: All transparent things—air, water, and the “uppermost shell of the physical Cosmos”—contain a certain substance that has the power of becoming transparent. It is actually transparent, however, only when excited to actuality by fire, or something resembling fire (such as the phosphorescence of certain fungi and decaying flesh). Light is not a body; it is the activity of the transparent medium. When the medium is actually transparent, color is able to set it in motion, thus to communicate the sensible form to the eye.

Aristotle’s discussion of sound and hearing is very accurate. He knows that sound is transmitted by vibration of the air, and he knows something of the anatomy of the ear. He remarks that voice, being “sound with a meaning,” indicates the presence of soul. Voice is not just air knocking against the windpipe: one must hold one’s breath to speak, using the confined air as an instrument.

Aristotle observes acutely that a study of touch raises the problem whether touch is or is not a single sense. For several pairs of opposites, not just one, are perceived by touch: hot and cold, dry and moist, hard and soft. People are inferior to other animals in some of the senses, notably smell, but exceed them all in touch and in its sub-sense, taste. This, Aristotle says, is the explanation of humanity’s superior intelligence and of the superiority of one person to another: “It is to differences in the organ of touch and to nothing else that the differences between man and man in respect of natural endowment are due; men whose flesh is hard are ill-endowed by nature, men whose flesh is soft, well-endowed.” Only solutions can be tasted, Aristotle argues. The organ of taste must be something dry that can be liquefied.

All sensation is via a medium. The Greek atomist Democritus erred in supposing that one can see through a vacuum. One cannot see something placed directly on the eye or hear something on the eardrum. Neither can one smell something in the nostril, unless one is breathing in. (Aristotle was puzzled, however, to find that some bloodless animals, which do not breathe, nonetheless can smell. He suggests that over the intranasal organ of smell people have some sort of curtain, analogous to the eyelid, which is raised only when people inhale. This the bloodless animals presumably lack.) Even the sense of touch has its medium, to wit, the flesh, which is not itself the sense organ.

Book 3 begins with a complicated proof that there could not be a sixth sense, nor a need for one. Aristotle continues with a discussion of the relation of the sensible object to the percipient sense. They are distinct, though their activity is one and the same: For example, the hearing and the soul are “merged in one.” Both must be “found in that which has the faculty of hearing; . . . actual hearing and actual sounding appear and disappear from existence at one and the same moment.” However, Aristotle is no Berkeleian: as potentialities, one of them may exist without the other. It is wrong to say that without sight there is no white or black; this description applies only to the actualities, not to the potentialities.

There follows an obscure passage in which Aristotle seems to say that after all one does need—and indeed, has—a sixth sense, a “common sense” that discriminates between sensations in different modalities: How else could one tell that sweet is different from white? This passage serves as a transition to the consideration of thinking and imagining that occupies most of the rest of the book.

Thought and Imagination

Thinking is different from perceiving (a doctrine denied by some ancient philosophers), for perception does not admit of error, while thinking does, and all animals perceive, but very few think. Imagining is different from both, as being in the province of the will and not productive of emotion.

Thinking is part imagination, part judgment. Imagination is “that in virtue of which an image arises for us.” It is not sensing, for it takes place in dreams; it is not always present, as sense is; imaginations are mostly false, while sensations are always true; when one (in fact) sees a person, one does not say that one imagines it to be a person; and visions appear to one even when one’s eyes are shut. Nor is imagination knowledge or intelligence or opinion, for brutes imagine but do not believe. Nevertheless, imagination is impossible without sensation: one does not imagine what one has never sensed. Imagination is “a movement resulting from an actual exercise or a power of sense.”

Mind is “the part of the soul with which the soul knows and thinks.” Thinking, though it is not perceiving, is sufficiently like perceiving to enable one to conclude that mind is capable of being affected by forms: “Mind must be related to what is thinkable, as sense is to what is sensible.” It follows that mind can have no nature (no combination of matter and form) of its own; for unlike the senses, the matter of which restricts their potentialities each to a certain range of possible sensations, mind is not limited in its objects. Hence, mind “before it thinks is not actually any real thing. For this reason, it cannot reasonably be regarded as blended with the body.” It is (potentially, not actually) “the place of forms.”

The mind so far described, however, is only “passive mind.” In the extremely short, obscure, and important fifth chapter, Aristotle says that though passive mind “is what it is by virtue of becoming all things,” there is “another which is what it is by virtue of making all things: this is a sort of positive state like light, for in a sense light makes potential colors into actual colors.” This kind of mind “is not at one time knowing and at another not. When mind is set free from its present conditions it appears as just what it is and nothing more: this alone is immortal and eternal (we do not, however, remember its former activity because, while mind in this sense is impassible, mind as passive is destructible), and without it nothing thinks.”

The remainder of the book is in the main a sort of appendix in which topics previously treated are considered further.

The great conception of On the Soul is that of soul as the function of the body. On this account, it is the only ancient treatise that is akin in its viewpoint to modern psychology and philosophy of mind. It is tragic that Aristotle’s great authority, which sufficed to canonize so many errors for so long in other departments of science and philosophy, did not prevail in psychology. Aristotle, like the tragic heroes he describes in De poetica (c. 334-323 b.c.e.; Poetics, 1705), was not blameless in the matter: His flaw was his abandonment of his own doctrine in order to sing the ode to “active mind.” Although the progress of many a science has consisted in throwing off Aristotelian shackles, the reverse is true in psychology, in which Aristotle’s insight had to wait almost until the twentieth century to be rediscovered.

Principal Ideas Advanced

•The soul is the actual development of the potentialities of life; it is the body’s source of movement, the essence of the living body, and the purpose for which the body exists.

•Sensation is the process of receiving into oneself, by means of the sense organs, the forms of things.

•The mind is that part of the soul by which the soul knows and thinks.