On the Soul

Having completed his account of the senses, Aristotle now seeks to answer some new questions. How do we explain the fact that we are aware of our sense perceptions—that we in a sense see ourselves seeing? Is there then an additional sense? Do the senses perceive themselves? Secondly, how do we distinguish one sense from another? How do we know that we are, say, seeing a black color rather than tasting a sweet flavor?

Aristotle concludes that there must be a larger principle of unity in the senses that explains how they interact. There is a principle by which we perceive that different senses perceive different things. The faculty of sense perception is single in essence but multiple in activity, which enables it to be simultaneously affected by different things—for example, color and sound.

Sense perception is a kind of concord or harmony, a mean between opposites. For example, the sense of hearing is gratified by a sound that is neither too high nor too low. Further, the senses can exist in potentiality or actuality. For example, an animal with hearing can be not hearing at a particular moment, but once a sound reaches its ears, its hearing is actualized.

Aristotle now discusses the faculty of the soul called imagination (in Greek, phantasia). He seeks to distinguish imagining from such activities as perceiving, believing, and thinking. Perceiving and thinking are not the same, and for a number of reasons. For one, perception of objects is always true, whereas thinking admits of being false. Perception is enjoyed by all animals, whereas thinking is enjoyed only by the rational animal, man.

Imagination is different from both perception and understanding. It is “that in virtue of which we say that an image [or an appearance] occurs to us” (198). Imagination comes about as a result of sense perception. Because imagination includes mental “images,” it resembles sense perception yet is distinct from it. Imagination can in turn result in supposition, a type of thinking that involves making judgments about truth and falsehood. Thus, imagination aids in making judgments about truth and falsehood, but it is not itself the faculty that does this.

Imagination is of things that could or might be; we look at the objects of imagination much as we look at a picture, without becoming emotionally involved as we would be if we believed the things to be true. Animals other than man have imagination, but none of them have belief, which is accompanied by conviction and thus is a rational activity exclusive to man. Moreover, most animals have perception, but none besides man have belief. For all these reasons it is clear that imagination is different from perception and from belief.

The intellect is “that part of the soul by which it has both cognition and understanding” (201). It is that part of the soul whereby it “thinks and supposes” (202). Aristotle compares thinking to perceiving. In both cases like affects like. Intellect stands in relation to objects of thought in the same way that sense perception stands in relation to objects of sense.

Yet the sense faculty and intellect are also different in some respects. The sense faculty is embedded in the body, while the intellect is separate. Further, intellect becomes more vigorous when exercised through difficult matter, whereas the senses become dulled when assaulted with “excessively perceptible” things, such as very loud sounds. Sense perception perceives the qualities of things (e.g., the wetness of water), while the intellect perceives their being. In other words, the intellect perceives things as abstracted or separate from matter.

Aristotle postulates that there are two parts to the intellect: an active and a passive (or potential) part. All beings with intellect have the capacity to know, but this process must be put in motion, so to speak. It is the active intellect that does this. The active intellect brings the animal’s intellectual potential into actuality, similar to how light illuminates colors and allows them to be seen by the eye. This active intellect is “separate, unaffected and unmixed” (205); it is “immortal and eternal,” whereas the passive intellect is perishable.

Aristotle deals with the nature of thought and propositional assertions of truth, or “veridicity.” Truth statements are complex, consisting of a “synthesis of thoughts, which are treated as though they were one” (205). Further, “assertion is of something and that something is the case” (207) and admits of truth or falsity.

Aristotle continues his discussion of thought and sense perception, summarizing a number of previously stated ideas, including that of potentiality and actuality. All things that come to be do so from something that exists in actuality. Thus, although potential knowledge comes before actual knowledge in time, the fact that actual knowledge is what brings it about means that actual knowledge preexists potential knowledge in a certain sense. A similar process happens in sense perception: The perceived object “converts the perceptive faculty from being it in potentiality to being it in actuality, without being itself affected or altered” (208).

Comparing sense perception and thought, we can say that perceiving is analogous to saying and thinking. Likewise, when we perceive something pleasant or painful, we pursue the pleasant thing or avoid the painful thing; this is analogous to assertion and denial in thought. In thinking, images (from the imagination) play a role analogous to perceived objects in sense perception; in fact, the soul never thinks without an image.

Aristotle sums up the discussion on thought and the cognitive function of the soul. Because of its ability to perceive all existing things either by sense or thought, the soul in a sense is all things. Thus, “knowledge is in a way the things that are known, perception in a way the things that are perceived” (210). Both sense perception and thought come about through a process of potentiality being brought to actuality. Sense perception and thought take in the forms of their objects without their matter. Sense perception and thought are interrelated, to the extent that “if one perceived nothing one would learn and understand nothing” (210). Similarly, we always think with images, which are supplied by the imagination.

The soul of animals has two main capacities: discernment (which includes both sense perception and thought) and movement. In this final group of chapters, Aristotle deals with motivation: the process of movement, whether physical or psychological.

Aristotle asks what part of the soul produces movement. Different philosophers have proposed different schemes. Are the movements of growth and decay produced by the nutritive part? This may be. However, locomotion (physical movement from place to place) cannot be produced by the nutritive part since it is accompanied by imagination and desire, which is not true of nutrition. Desire and avoidance are in fact powerful motivational factors in animals. Yet desire itself cannot be the sole producer of movement, since some people are able to control their desires.

The two motivational faculties of the soul are desire and intellect (including imagination as well as rational thought). We act based on our imagination or on knowledge gained through reasoning. Thus, desire is purpose-directed and “the object of desire is the point of departure for action” (214).

In fact, movement can be reduced to a single instigating factor: desire. For it is desire that starts the whole process, giving the intellect a goal to aim at. The object of desire is the good or what seems good. There are three things involved in this process: the object of desire, the desire, and the animal.

Aristotle makes some final considerations about desire and movement. Nonhuman animals have desire and imagination but lack reason; thus, unlike human actions, their actions are not deliberative. When an animal (whether human or nonhuman) is torn between two desires, nature dictates that the “loftier” (higher) of the two will win out. Uniquely in human beings, desire triggers a rational thought process to determine how to gain the object of desire. This process of deliberation includes three steps: supposition, thought, and reason, each of which becomes more specific in its judgment of the course of action to be taken.

All living things have a nutritive soul that nourishes and causes growth in the body, “from birth to destruction” (217). However, not all living things (e.g., plants) have perception or need it. All animals need and have perception, of which the most essential is touch. Touch is thus necessary for the preservation of an animal’s life. All other senses are for the sake of living well, but touch is necessary for life itself.

Touch is a sort of mean between all tangible things. The other senses perceive through a medium (e.g., sound through the medium of air), but touch is perceived through itself, as it were; this is why it has no particular sense organ but instead feels through the flesh itself. Thus, touch comes into direct contact with objects in the world around us in a way that no other sense does.

Without touch there could be no other sense. In fact, the destruction of touch signals the death of the animal because it is the most essential and necessary sense. This is seen from the fact that touching something dangerously hot or cold can kill an animal.