Aristotle Essay, Research Paper
Aristotle’s approach in describing sense perception in De Anima is in many ways similar to modern ones. He makes an attempt to explain all forms of perception – seeing, hearing, touching, smelling and tasting – in purely physiological terms. Although he lacked our knowledge of nerve endings, ear drums, retinas etc., having instead the rather primitive view that the sense organs are made of earth, air, water and fire, his overall description of how we perceive things in the physical world nevertheless bears a number of striking resemblances to the more refined modern explanations. Naturally, there have been several criticisms of Aristotle’s account of sense-perception, and one such will be discussed below. However, more importantly, it will be argued that there are certain basic philosophical problems which accompany not only Aristotle’s theory of perception, but contemporary ones as well.
Form and Matter
Although Aristotle discusses each of the five senses at considerable length, it will suffice us here to focus primarily on visual perception, as his handling of this particular sense has parallels in his treatment of the other senses. Before we get into the mechanics of how an animal actually sees things in the physical world, however, it will be necessary to explain briefly Aristotle’s distinction between form and matter. Matter, according to Aristotle, is that which a thing is made of. Form, on the other hand, is that quality or shape which a thing has that makes it belong to a particular class of things. Aristotle gives the example of a signet ring being dipped in wax and making an imprint. The imprint is the form of the ring, but not the ring itself, i.e. its matter. (Book II, chapter 12) A useful modern example which shows the distinction between form and matter might be a photograph of, for example, a person. The photograph has captured the form of the person (i.e. his or her physical attributes), but is obviously not actually the person.
Aristotle’s Theory of Perception in Brief
According to Aristotle, when an animal perceives an object, the sense organ (in the case of visual perception, the eye) takes on or actually becomes like the form of the object it is perceiving. In describing this process, Aristotle uses two technical terms: potentiality and actuality. Let’s imagine a person called Bob who is looking at an orange. The orange has the form of an orange in actuality. Before he looks at it, Bob’s eye has the potential for receiving or becoming the form of the orange. As soon as he starts to look at it, however, his sense organ becomes “acted upon” and undergoes change. In the words of Aristotle: “…when once it [the sense-organ] has been acted upon, it is similar and has the same character as the sensible object.” (Book II, chapter 5) Thus Bob’s eye eventually takes on the actual form of the orange. This, according to Aristotle, is essentially how sense perception works.
There are, however, some added features in his theory that need to be mentioned. To begin with, Aristotle believed that we don’t perceive anything directly. Instead we perceive things indirectly, through some sort of medium. This medium varies from sense to sense. In the case of hearing, for example, it is air. In the case of seeing, it is air which contains something Aristotle chooses to call the “transparent,” which is closely related to light. (Book II, chapter 7) According to T.W. Bynum’s interpretation in his article “A New Look at Aristotle’s Theory of Perception,” the transparent does not have an independent existence, but is always found in something else, usually air, water or aether, the eternal fifth element (see the third paragraph of my paper on Aristotle’s astronomy).  Light is the activity of the transparent. In the absence of light, the transparent is only potentially active, and this is what is called darkness.
Let us return to Bob’s orange. Let’s also assume it’s a normal orange and has orange as its color. According to Aristotle, the color of the orange causes the transparent medium, in this case air, to move. (Book II, chapter 7) The medium is continuous, and thus the motion that is produced in it eventually reaches Bob’s eye, causing it to see orange. To prove that this is the case, Aristotle points out that if you place a colored object on your eye, you won’t see it. This is because there is no intervening medium between the object and the sense organ.
According to Aristotle, once the sense organ has become like the form of the object it is perceiving, it sends a “percept” which travels through the blood vessels to the so-called sensus communis, the primary perceptual faculty. The sensus communis is located in the heart region, and has as its function to discriminate between the “percepts” it is receiving from the various sense organs, which it then judges and interprets.  (Book III, chapter 2) In the case of Bob, it is the percept of the orange that travels from the eye to the sensus communis. It is important to note that Aristotle talks about the sensus communis as “judging,” because this commits him to the view that we are not necessarily perceiving the world as it actually is, but are rather “interpreting” it on our own terms. This view is similar to a modern one which will be discussed below.
A Critique of Aristotle’s Theory of Perception
In an article entitled “Aristotle on Sense Perception,” Thomas J. Slakey tries to show that Aristotle’s theory of sense perception has little explanatory value. He quotes the following passage from De Anima (the Oxford translation by J. A. Smith):
This implies that the sense [itself] is a `mean’ [mesotes] between any two opposite qualities which determine the field of that sense. It is to this that it owes its power of discerning the objects in that field. What is `in the middle’ is fitted to discern; relatively to either extreme it can put itself in place of the other.
(De Anima 424a 4-7)
He then interprets Aristotle as making the following distinction between sense and sense-organ: “the sense-organ is a part of the body which becomes hot when heat is perceived, and so forth; each sense is located in a part of the body and is the power of the sense-organ to change in temperature or colour…”  Thus he concludes that: “There is no distinction between the change of the sense and the change of the sense-organ. The only distinction between `sense’ and `sense-organ’ is that the word `sense’ refers to the power of the sense-organ to change within a certain range of qualities.”  In other words, Slakey believes that Aristotle is trying to explain sense-perception merely in terms of the sense-organ becoming like the thing it is perceiving. It is simply a description of what happens to the sense organ, he argues, not an explanation of sense-perception.
It appears, however, that Slakey’s attack on Aristotle is due to a misreading of the passage just quoted from De Anima. Aristotle does not say that the sense is “the power of the sense-organ to change” as Slakey puts it, but rather that it is “the power of discerning the objects in that field.” [Italics mine] Thus Aristotle’s distinction between sense and sense-organ is quite marked. The sense-organ is that which takes on the form of the object that is acting upon it, whereas the sense is a “mean” between two extremes which can “perceive” (measure) the change that occurs in the sense-organ. In the case of Bob, when Bob’s eye (the sense-organ) takes on the form of the orange, the sense “perceives” (measures) this change in the eye. 
It seems, then, that Slakey’s criticism is unfounded. Of course, there is one problem with Aristotle’s account, and that is that he fails to mention what he means by the sense as “perceiving” (measuring) the change of the sense-organ. He appears, in fact, to be trapped in a vicious circle by simply describing perception as “perceiving.”
Comparing Aristotle’s Theory with a Modern One
Despite this flaw, as T. W. Bynum points out in the aforementioned article, Aristotle’s account of sense perception is actually a very good one. It can easily be updated to correspond closely to some modern theories, by, for example, “replacing the heart with the brain; blood vessels with nerves; earth, air, fire and water with the elements of modern chemistry; and so on.”  There is, however, a fundamental distinction between Aristotle’s theory of perception and, for example, one that is currently gaining acceptance in our own day. It is what the linguist Ray Jackendoff, in his book Patterns in the Mind has chosen to call the “Construction of Experience.”
Whereas Aristotle believed that our senses are “passive” in the sense that they’re simply absorbing information about the outside world, and re-arranging and/or ordering it, Jackendoff argues that perceiving is to a large extent an “active” process. He says that we are constantly interpreting the data that come in through our senses, and that we often “fill in” or project certain innate concepts that we have onto our perceptions of the physical world. Of course, Aristotle also believes that we “interpret” the “percepts” that come to us from the sense-organs. However, he says nothing about “adding” to these percepts in the process of interpreting them, which is Jackendoff’s main point. To prove that we are indeed “constructing” our experience of the world, Jackendoff includes several drawings in his book which provoke the eye, or the brain rather, to “see” things which aren’t actually there. 
The Problem of Mental Images
Aristotle made an impressive start towards an explanation of sense perception, and through the centuries scientists have continued to develop even more accurate theories. However, upon further scrutiny, there seem to be certain conceptual problems that no theory so far can account for.
Let’s return once more to Bob and his orange for a minute. After he has looked at the orange, it is possible for him to close his eyes and still retain a “mental image” of the orange. This is what Aristotle called a perceptual trace, or phantasmata.  The question that we now have to answer is what inside Bob is it that is perceiving this perceptual trace of the orange? We can certainly talk of Bob as “seeing” the orange in his mind, yet what exactly do we mean by this? Aristotle did not seem to be troubled by this particular problem, as he offered no explanation for it. He merely states that perceptual traces are judged by the faculty of phantasia, which is located in the sensus communis, and that beings with intellect, such as humans, can manipulate these traces in various ways. 
The same problem seems to exist in our modern theories of sense perception. We talk about the eye as receiving reflected light from the object being perceived, which then becomes a “coded message” of some sort. This message is then sent to the brain, where it is “decoded” and interpreted as, for example, an orange. However, when we close our eyes and “see” the orange with our “mind’s eye,” what exactly does the image of the orange consist in, and what is it that’s actually “perceiving” the orange? There is at present an argument among scholars that all mental activity (i.e. activity of the “mind”) is the result of physical reactions in the brain.  However, there is as yet no explanation for what exactly it is that is happening when, for instance, someone like Bob is “seeing” an orange in his head. To simply say that a certain amount of neurons are being fired when this happens is not a satisfactory explanation. Individual neurons by themselves are not capable of visual perception, so to simply assert that some neurons are “watching” other neurons which embody the image of an orange, does not make for a convincing story.
The Problem of Consciousness and Other Minds
The problem of “seeing” things with the mind’s eye is closely connected to the problem of consciousness, which recently has become a topic of hot debate between various scientists and philosophers. Let us consider for a moment the case of animals other than humans. According to Aristotle, even the lowest forms of animals have sense perception of some kind, and they are able to discriminate between what is pleasant and what is painful. Depending on whether the object being perceived is food or, say, a predator, the animal knows what kind of behavior to initiate in each case, i.e. to ingest in the former and take flight in the latter. (Book III, chapter 7) Aristotle does not believe, however, that these animals “must employ `concepts’ like `pleasant’ or `non-food’…” as Bynum says.  These concepts are reserved for animals with “intellect” only. Rather, the behavior of the simpler animals is the result of basic stimulus-response mechanisms, which are purely automatic.
By “intellect,” Aristotle means the faculty by which we “know” and “understand,” or more generally, “think.” Thought is embedded in a larger cognitive whole, which includes the perceptual faculty and thereby can be said to be a function of the perceptual faculty. Unlike the faculty of phantasia (or “imagination”), which judges the “percepts” that come from our sense organs, “intellect” entails having beliefs and convictions. Aristotle acknowledges that many animals have phantasia, yet reserves “intellect” for humans only. (Book III, chapter 3) It is not clear, however, on what basis he makes this judgement. If he thinks of the “intellect” as dealing with propositional content, it may be that he draws this conclusion from the observation that only humans seem to have language.
In our own day, more rigorous attempts have been made to determine what kinds of concepts other animals use and to what extent they may be said to “think” and have consciousness. However, no definite conclusion has as yet been reached in this regard. In fact, it may even be that a satisfactory explanation is completely beyond our reach.
Two researchers called Dorothy L. Cheney and Robert M. Seyfarth have made a preliminary attempt at explaining the minds of vervet monkeys in their book How Monkeys see the World.  Through long periods of observation and experimentation, they have been able to record an impressive amount of data and draw some tentative conclusions. However, how accurate can an explanation of the monkeys’ minds be that is based solely on observation from the “outside”? As Thomas Nagel cogently argues in his famous article, “What Is It Like to Be a Bat?”, the only way to know how a bat experiences the world is to be somehow able to “see” things completely from the bat’s point of view. However, since this is physically (logically?) impossible, a complete explanation or understanding of the bat’s experiences will not be forthcoming.  The same would have to be said concerning the vervet monkeys.
There are, as we have seen, problems both with Aristotle’s and with modern theories of sense perception. None can account for the kind of “seeing” that goes on in our mind’s eye, and none can account for the precise subjective experience of other animals. Modern theories are certainly improvements in many ways over Aristotle’s, yet several of the same philosophical problems surrounding the issue of sense perception persist. Aristotle made an important contribution to Greek science by being the first to propound a physiological theory of perception and a philosophy of mind. His treatment of the senses and the mind laid the groundwork for the debates which continue into our own day.
Cheney, Dorothy L. and Robert M. Seyfarth. How Monkeys see the World. Chicago: University of Chicago Press, 1990.
Dennett, Daniel C. Consciousness Explained. Boston: Little, Brown & Company, 1991.
Durrant, Michael, ed. Aristotle’s De Anima In Focus. London and New York: Routledge, 1993.
Nagel, Thomas “What Is It Like to Be a Bat?” The Philosophical Review, vol. LXXIII, no. 4, October 1974. 435-450