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 psych 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, psych meant “life-principle,” whether simple or complex, the inner cause of vital movements of all kinds.
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.
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...
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 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...
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...
Adler, Mortimer J. Aristotle for Everybody: Difficult Thought Made Easy. New York: Macmillan, 1978. Adler gives an excellent introduction to Aristotle’s thinking for readers new to the philosopher. The book describes Aristotle’s approach to philosophy and the arguments presented in his major works in clear, modern language.
Elders, Leon. “The Aristotelian Commentaries of St. Thomas Aquinas.” Review of Metaphysics 63, no. 1 (September, 2009): 29-53. An excellent discussion of the large body of work done by Aquinas on various aspects of Aristotle’s thought. Elders’s section on the soul and De anima is particularly insightful on the relationship...