Why do we have sense-organs? We have ears, intricate structures composed of membranes, bones, channels, etc., a nose with two nostrils and a mucous membrane which covers a nasal cavity. We have taste buds, a range of tactile sensors under our skin, not to mention the eyes. Why?

The simple answer is that we have sense-organs because they enable us to perceive. A sense-organ, as Aristotle would say, is an organon, a tool or instrument of perception. But to understand why the sense-organ is instrumental in perception we must understand something about perception. Just as we must understand something about gardening before we can appreciate the usefulness of a rake, so we must understand something about sense-perception before we can see the point of having a sense-organ. An explanation of the sense-organs must therefore start with an understanding of what sense-perception is. Once we understand what sense-perception is, we can explain how the sense-organs help bring about sense-perception as we have understood it.

In modern science it can be taken for granted that the explanation of perception will refer to physical processes. For example, vision is said to be the process whereby the eyes ‘feed the brain with information coded into neural activity — chains of electrical impulses — which by their code and the patterns of brain activity, represent objects’.

Introduction

In this chapter I want to explain how, according to Aristotle, the medium of perception works. The discussion focuses on the medium of vision, that is, the transparent. In chapter I we saw how the transparent dominates Aristotle's account of the sense-organ of vision. Aristotle said that the inside of the eye had to be actually transparent (light) just as the medium in between the sense-object and the eye had to be actually transparent. I argued that this meant that the inside of the eye had to be transparent in order to be able to receive the sense-quality and mediate it to the seat of perception around the heart. The role of the transparent both outside the eye and inside the eye was to mediate the sense-quality.

In this chapter I shall inquire into the role of the transparent as a medium. This inquiry follows on the argument of chapter I. For if I was right in chapter I, this inquiry will not only affect the way we understand the transparent medium in between the eye and the sense-object as working but also the way in which we understand the transparent inside the eye as working for, according to chapter I, the role of the transparent inside the eye was the same as the transparent outside the eye.

To conclude, I wish to relate the various strands of the argument to the questions that I raised in the Introduction. In particular, I want to explore whether Aristotle's explanation of the sense-organs sheds any light on the functionalist debate.

I began this study by asking why we have sense-organs. Aristotle's answer was based on the idea that the sense-faculties are potentialities to be changed by certain objects. These potentialities are found only in certain sorts of matter. That was why we needed sense-organs. The sense-organs were the necessary material basis of perception. The matter had to be matter of a certain sort. For example, the ability to be changed by colours was known as transparency. But transparency was found only in certain sorts of matter, such as water. That was why the organ of vision was made of water. Similarly, the ability to be changed by sound was found only in matter that was resonant, such as air. That was why the organ of hearing was made of air. The ability to be changed by odours was found in water or air because both were potentially like odours, dry. So the organ of smell was made of water or air. The organ of touch consisted of all the elements, for it was only a mixture of the four elements that would make the sense-organ potentially like all the tangible qualities, the proper objects of touch.

What is perceiving?

My analysis of the sense-organs has followed the same pattern. There are two central claims. (1) The sense-faculty is defined by its ability to be changed by the sense-object as such. This ability belongs to an attribute. For instance, the ability to be changed by sound belongs to resonance. (2) The attribute is present only in a certain sort of matter. This, for example, is why we have an ear whose inside is composed of still air, for it is only still air (or water) that is resonant. The sense-organ is here hypothetically necessary in the same way that iron is necessary if the saw is to have the ability to saw.

The sense-organ is in this way explained as a necessary material basis for the first actuality that defines the sense-faculty. The analysis shows that a material basis is necessary if the first actuality to be changed by a certain sort of sense-object is to be present. So far then the focus has been on the relationship between the first actuality and the matter or potentiality of the sense-organ. The analysis has not shown that a material basis is necessary because the first actuality can only be actualised in a material change. Suggestions have been made at various points to the effect that there need be no material changes in perception.

The argument

This study aims to answer two questions in Aristotle. First, why do we have sense-organs? Second, why are the sense-organs composed the way they are? Aristotle's theory of the sense-organs, I shall argue, is briefly this. We have five so-called special senses: sight, hearing, touch, taste and smell. The five senses are powers or potentialities δυνάµειϚ that animals have to perceive certain objects — for example sight is the power to perceive colour while hearing is the power to perceive sound. The power to perceive a sense-object consists in the ability to be changed by the sense-object. When an animal perceives a sense-object, its sense-faculty is changed by the sense-object so as to become like the sense-object, for example when I see a red pillar box then my faculty of sight becomes red in a certain way. This ability that the sense-faculty has to be changed by a certain sense-object is what defines the sense-faculty, for example the faculty of sight is defined as what has the ability to be changed by colour. The faculty of hearing is defined as what has the ability to be changed by sounds, and so on.

The ability to be changed by a sense-object is something that is only found in matter.

Touch is the sense of direct contact

The verb ‘to touch’ can be used in two ways. We can say that a bottle touches the table. By this we may mean that the bottle is in direct contact with the table, that there is nothing in between the two. However, when I say that I touch the hardness of the table I may mean something different, namely, that I feel or perceive the hardness of the table. I touch the table in this way only when I am using my sense of touch. Similarly, we can say that the touch of your hand is cold. In that case too it is implied that I perceive your hand as cold by my sense of touch.

Perhaps it is more usual to use the verb ‘to feel’ rather than the verb ‘to touch’ as a verb of perception. One would say ‘I feel the hardness of the table’ rather than ‘I touch it’ if one wants to say that I perceive the table rather than that I am simply leaning on it with some part of my body. That is perhaps also why it seems more natural to use the verb ‘to touch’ when the idea is just that there is contact between two things and no perception takes place.

What is hearing?

The explanation of the faculty of hearing and its organ, the ear, follows the same pattern as the explanation of sight and the eye. We need to understand first of all what sound is, for sound as the proper object of hearing is the actuality that explains the potentiality of hearing. Once we know what the potentiality of hearing is we can explain the sense-organ as the matter required for the presence of this potentiality.

The production of sound

Sound is produced, Aristotle says at De Anima 11.8 419b4–7, by objects that are solid and smooth, a gong, for instance. Such objects are said to ‘have sound’ and to have the potentiality to make a sound. Aristotle explains the potentiality of such objects as the ability ‘to produce an actual sound in between itself and the sense of hearing’. So direct reference is made to the sense of hearing in this initial explanation of what a potentiality to make a sound is. The reference to the sense of hearing is obviously not just meant to locate the sound spatially, that is it is not just supposed to tell us that the sound occurs somewhere in between the sounding object and the sense of hearing.

SIN AS CONTRADICTION

If Tertullian finds antithesis in the world and God, he will have no trouble finding it in human beings. Everyone had found contradictions in the human person, which was racked by every kind of tension – soul/body, reason/passion, saint/sinner and free/enslaved. A part of European culture, east and west, is the history of Paul's struggle (‘the good that I would, I do not: but the evil which I would not, that I do’), narrowly anticipated in Ovid (‘I see and approve better things, but follow worse’) and repeated in Augustine (‘What shall wretched man do?).

Always Tertullian's antitheses come, not from perversity, but from a sense of reality. His own reality was dominated by his consciousness of slavery to sin and the deliverance of baptism. At the last judgement, he would remember the adulteries with which he had once stained his flesh, and be confident that God would raise that flesh which Christ had long since cleansed in baptism (res. 59.3). Sin was the supreme contradiction, for it denied God and destroyed humanity. Platonists like Clement could doubt the ultimate reality of evil. Heraclitean Stoics like Tertullian could only face reality when evil and sin were taken seriously. Tertullian, like Paul, thought and wrote a lot about sin. He made the first moves toward a doctrine of original sin and his views on the forgiveness of sins caused conflict with the hierarchy of the church.