41. Because this assertion is contrary to the appearance, however, it may seem not to merit credence unless it is demonstrated, and since it cannot be demonstrated except by illustrations that a person can perceive with his physical power of sensation, therefore we will demonstrate it by recourse to such. A person has five outward senses, which we call touch, taste, smell, hearing and sight. The subject of which the sense of touch is predicated is the skin that envelops a person. The very substance and form of the skin cause it to feel whatever is brought into contact with it. The sensation of touch does not exist in those things which are brought into contact with it, but it exists in the substance and form of the skin, which are the subject of which it is predicated. The sensation is simply the affecting of it by the things brought into contact with it. The case is the same with taste. This sensation is simply the affecting of the substance and form which constitute the tongue. The tongue is the subject of which it is predicated. It is the same with the sense of smell. People know that an odor affects the nostrils and is sensed in the nostrils, and that it is an affecting of them by odorous emanations coming into contact with them. So, too, with hearing. It seems as though the hearing of a thing exists in the place where the sound originates; but the hearing is in the ear, and is an affecting of its substance and form. The hearing of things at a distance by the ear is only an appearance. [2] It is the same with sight. When a person sees objects at a distance, it seems as though the sight exists there, but in fact it is in the eye, which is the subject of which it is predicated, and the sight is similarly the affecting of it. Distance is only a conclusion of the judgment regarding the intervening space based on the objects that lie in between, or on the dwindling and consequent fading of the object seen, the image of which is produced within the eye in accordance with its angle of incidence. It is apparent 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. For the case is the same with sight as it is with hearing. Hearing does not go out from the ear to capture sound, but sound enters the ear and affects it. [3] From these illustrations it can be seen that the affecting of the substance and form which produces a sensation is not something separate from the subject of which it is predicated, but simply causes a change of state in it, the subject remaining still the subject it was before and that it continues to be thereafter. It follows as a consequence that sight, hearing, smell, taste and touch are not some aerial emanation flowing out from their organs, but that they are the organs regarded in terms of their substance and form, the affecting of which produces sensation.