41. Since this truth is counter to appearance, though, it may seem unworthy of credence unless some evidence is supplied; and since the only way to supply evidence is with the kinds of thing we perceive with our physical senses, that is what I need to draw on.
We have five external senses, called touch, taste, smell, hearing, and sight. The subject of touch is the skin that envelops us: the very substance and form of the skin make it feel what comes into contact with it. The sense of touch is not in the things that come into contact with it but in the substance and form of the skin. That is the subject, and the sense itself is simply the way it is affected by contact.
It is the same with taste. This sense is simply the way a substance and form, this time of the tongue, are affected. The tongue is the subject. It is the same with smell. We recognize that odors affect the nostrils and are in the nostrils, and that smell is the way impinging aromas affect them. It is the same with hearing. It seems as though hearing were in the place where the sound originates, but hearing is in the ear and is the way its substance and form are affected. It is only an appearance that hearing happens at a distance from the ear.
This is true of sight as well. When we see objects at a distance, it seems as though our sight were where they are. However, sight is in the eye, which is the subject; and sight is the way the eye is affected, too. Distance is simply what we infer about space on the basis of intervening objects or on the basis of reduced size and consequent loss of clarity of an object whose image is being presented within the eye according to its angle of incidence. We can see from this that sight does not go out from the eye to the object, but that an image of the object enters the eye and affects its substance and form. It is the same for both sight and hearing. Hearing does not go out of the ear to seize on the sound, but the sound enters the ear and affects it.
It stands to reason, then, that the affecting of substance and form that constitutes a sense is not something separate from the subject. It is simply the effecting of a change within the subject, with the subject remaining the subject throughout and thereafter. It then follows that sight, hearing, smell, taste, and touch are not things that go floating out from their organs. They are the organs themselves, in respect to their substance and form. Sensation happens when they are affected.
