LECTIO TWENTY-THREE

             § 530. Having shown how the sense of touch requires a medium that is of the nature of the one who touches, the Philosopher goes on to ask whether it needs an extraneous medium. And his answer contains two points: first, he shows that touch does not occur without an extraneous medium; next, at 'The question, then, is whether', he shows how touch and taste differ from other senses which perceive through an extraneous medium.

             First, then, he remarks that in the case of touch one might doubt whether it has an extraneous medium, since we have seen that the medium of touch is a natural part of us. The doubt assumes that every body has depth, i.e. a third dimension. And indeed it is clear that every body has three dimensions, length, breadth and depth; whence it follows that whenever two bodies have another between them, the former bodies are not in direct contact; they must be divided by a dimension.

             § 531. It is also evident that wherever there is a liquid or wet medium, there must be a body of some sort. For wetness is a quality and must exist in a body as its subject. Either then it resides in a body essentially, and then there is a liquid, e.g. water; or it exists in virtue of some adventitious body, in which case there is something that is wet, i.e. having water either on its surface only, or on its surface and throughout as well; so he says that every humid or wet body must either be liquid or 'contain' liquid. Now it is clear that bodies which touch in water have water as a medium between them covering their outer surfaces--otherwise they would be dry in water, which is impossible; for whatever things are in water must be wet, in the sense that water covers their surfaces. Water, then, is the medium between two things touching in water; whence it follows that it is impossible that one body should touch another in water immediately. And the same holds good for air, which is a fluid like water.

             § 532. For the air flows round the things that are in the air as water around things which are in water; but it is much less noticeable to us that air is a medium of this kind than that water is, on account of our being continually in the air so that it envelops us imperceptibly. In the same way, animals that live in water are not aware that when two bodies touch one another their surfaces are wet; for, being habitually in water, they do not notice the water between them and the bodies they are touching. There is also this other reason why the fact is less evident to us in the case of air than water: that air is more subtle and less perceptible to sense. Whenever, then, we touch anything there is always a medium between ourselves and the thing touched, whether air or water.

             § 533. But a question suggests itself. The medium for any sense should be lacking in the sensible qualities perceived by it,--like the colourless diaphanum. But obviously air and water have tangible qualities; so it seems they cannot be the medium for touch.

             § 534. Averroes answers that we are not affected by pure air or pure water. Nothing is passively affected, he says, save by its opposite, in accordance with the principle of passivity; but air and water are not contrary to us, they are indeed akin to us, in the same way as place to what is located in it. Hence our touch is not affected by air and water, but by qualities extraneous to them. What tangible qualities are perceived in air and water are due to their combination with extraneous bodies. As fire never loses its heat, so water never loses the quality proper to water; and if we ever perceive heat, this is due to the admixture of some extraneous body.

             § 535. Now this reply contains several errors. First, it is false to assert that air and water do not affect our bodies, as being akin to these in the manner of a locality to what is placed in it. For, clearly, our bodies get their place in nature, as also their natural movement, from the element that predominates in them; and, consequently, are related to locality and material environment as elements located to elements locating. But contiguous elements mutually affect one another at the points of contact, as is shown in the Meteorologica, Book I. Our bodies therefore are naturally subject to the influence of the elements.

             § 536. Again, everything in potency is, as such, disposed to receive the influence of what is in act; and our bodies, being in a mean state between the extremes of the tangible qualities in the elements, are related to these qualities as potency to act. For, as we shall see, a mean is in potency to extremes. It is evident, then, that our bodies are disposed to be influenced by the elemental qualities, and to perceive them.

             § 537. This error of Averroes comes from his failing to distinguish between the elements as contrary to, and as akin to and containing (as the locality contains the located), one another.

             § 538. Note then that the elements can be considered in two ways: in one way, in terms of active and passive qualities, and in this sense they are contrary to one another and act upon one another at their points of contact; but in another way, in terms of their substantial forms derived from the influence of the heavenly bodies. Now the elements are formal in the degree that they are akin to the heavenly bodies; and since it is of the essence of form to have the character of an inclusive whole, it follows that a superior body as such contains its inferior, and stands to the latter as a whole to a part which, though a part, is yet a distinct being; which is precisely the relation of locality to the located. And therefore the function of locating and containing is derived to the elements from the primary locating principle, the heavenly body. Whence it follows too that locality and local motion pertain to the elements in virtue of their substantial forms, not of their active and passive qualities.

             § 539. Another error is this, that he says that air and water undergo no changes save by mixing with something extraneous. For it is evident that air and water are in some degree destructible; but destruction and generation can take place in the elements without any mixing and yet involve change, as is proved in the De Generatione. Therefore, so long as water remains water, its natural quality can be changed without the admixture of anything extraneous. The case of fire is quite different; being the most formal and active of the elements, the rest are material in relation to it, as Aristotle says in Book IV of the Meteorologica.

             § 540. It may be said, then, that air and water are easily changeable by extraneous qualities, especially in small quantities such as the amount of air and water between two bodies that touch one another. This is why the sense of touch is not impeded by the medium of water or air. And, of the two, air is less an impediment than water, for its tangible qualities are scarcely perceptible at all. But an intensification of the tangible qualities of air or water, as when they become extremely hot or cold, does of course impede the sense of touch.

             § 541. Then, when he says 'The question, etc.', he shows the difference between touch and taste on the one hand, and the rest of the senses on the other: first rejecting a supposed ground of differentiation; secondly, stating the true difference, at 'But the tangible differs.' In the first place, then, he says that this question of the extraneous medium of touch leads one to ask whether the sensation of all sense objects occurs in the same way, or diversely for diverse objects--as, at first sight, it does seem that touch and taste perceive by immediate contact, whilst the other senses apprehend their objects at a distance.

             § 542. But this difference is illusory; we do in fact perceive the hard and the soft and other tangible qualities 'through something intervening', an extraneous medium, like the objects of other senses, the audible, the visible and the odorous. But whilst the latter objects are sometimes a long way from the sense, the tasteable and tangible are so close that the medium is practically imperceptible and passes unnoticed. We perceive all sense-objects through an extraneous medium, but this is not noticeable in taste and touch; to repeat what we said before, if the medium of touch were a membrane that covered us without our noticing it, we should feel through a medium in a manner similar to the way we do actually feel in air or water. For as it is, we fancy we touch the sense objects themselves, and that there is no medium.

             § 543. Then at 'But the tangible differs', having rejected the false difference he states the true one, observing that tangible objects differ from visible and audible in that, whereas we perceive the latter because they set in motion the medium, and the medium in turn moves us, we perceive tangible objects, not because the medium has first moved us, but as being moved simultaneously with the medium, by the sense-object. It is as when a man is struck on his shield; the shield, being struck, does not then strike the man; man and shield are struck simultaneously.

             § 544. Nor is this simultaneity to be understood in the order of time only; for in sight the medium is affected by the visible and the eye by the medium, and yet sight occurs without succession in time. Smelling and hearing, however, take place with some temporal succession, as it is said in the De Sensu et Sensato. The succession is due to the way the cause of the action operates; for whereas in the other senses a change in the medium is itself the cause of the sense being affected, it is not so in touch; for in other sensations the medium is present of necessity, whilst it is only as it were an accidental accompaniment of touch, due to the fact, for example, that the bodies in contact are moist.

             § 545. Next, when he says 'It would seem in general', he concludes to the truth about the sense of touch: with regard (a) to the medium; (b) to the organ, at 'Tangible objects vary', and (c) to the object apprehended by this sense, at 'Further: as sight etc.'. First, then, he observes that the flesh and the tongue seem to be related to the organ of touch as air and water to the organs of sight, hearing and smell. Now in none of these latter senses can sensation occur if the organ itself is touched; thus a white body placed on the surface of the eye is invisible. Whence it follows that the organ of touch is within; for this sense works in the same way as in others; and if animals can perceive sense-objects placed on their flesh, it is evident that if flesh is not precisely a sense-organ it is certainly a medium of sensation.

             § 546. Then, at 'Tangible objects . . .', he explains the nature of the organ of touch. Tangible qualities, he says, are the differentiations of body precisely as body, i.e. those differences which diversify the elements, namely dry and wet, hot and cold, of which Aristotle treats in his work on the elements, the De Generatione et Corruptione.

             § 547. For it is clear that the organ of touch, wherein the sense called touch primarily resides, is a part of the body in potency to these differentiations. Every sense-organ is passive to its object, because sensation is a kind of receiving; if the sense-object, which is the agent in the operation, reduces the sense to a condition similar to itself, the sense was previously potentially such. This is why, in the degree that the organ of touch already actually has any quality, it does not perceive this quality. We do not feel a thing as hot or cold, hard or soft, in so far as these qualities are already present in the organ of touch; rather, we perceive such tangible qualities as exceed that mean state between contrasted tangibles in which this sense properly consists. For as a mean is potential to extremes, so the organ of touch can discern the extremes of tangible qualities. It can be affected by either extreme because, as compared with either, it has the nature of the other: e.g. as compared with heat the tepid is cool, but as compared with cold it is warm. Thus the mean is passive to both extremes, being in a way the opposite of each. As the organ that knows white and black has neither of these actually and both of them potentially (and the like is true of the other senses) so also is it, and necessarily, in the sense of touch: its organ is neither hot nor cold, but in potency to both.

             § 548. But this occurs in a special way in touch. In sight, for instance, the organ in potency to black and white is quite free from both black and white, for it is quite colourless. But in the case of touch the organ cannot be completely deprived of heat and cold, moisture and dryness, for it is composed of elements having these qualities essentially. Rather, the organ of touch is in potency to its objects as a mean between extremes, potential to either extreme. Whence it follows that the closer an animal's composition approaches the state of perfect balance, the finer will be its sense of touch; and that is why man, of all animals, has the finest touch, as we have seen.

             § 549. Next, at 'Further: as sight', he concludes about the object of touch. As sight, he says, is of the visible and invisible, and the other senses are also of opposites (as hearing of sound and silence), so touch is of both the tangible and the intangible. 'Intangible' is said in two ways: either of that which has a tangible quality to an excess which destroys the sense, like fire; or of that which has very slight tangibility, like air. Both are called intangible because both are hard to perceive by touch.

             § 550. Summing up, he says that he has treated 'in outline', that is, in a summary manner, of each of the several senses. For he deals with them more in detail in the De Sensu et Sensato.

424a 16-424b 20