CHAPTER XII

SENSITIVITY AND LIFE

TOUCH IS THE FUNDAMENTAL SENSE

             ALL LIVING THINGS HAVE THE VEGETATIVE SOUL; and this from generation to corruption. For every thing generated must grow, maintain itself and then decay; and this is impossible without nutriment. Of necessity, then, a vegetative power is found in all that is born and dies.§§ 847-8

             Sensation, however, is not necessarily found in everything that lives. Beings whose bodies are uncompounded even lack touch, without which no animal can exist at all; nor can those be animals which are unable to receive forms without matter.§§ 849-50

             But if Nature does nothing in vain, animals must have sensation. For all things in Nature exist for a purpose, or accompany that which exists for a purpose. Every body that is able to move about, if it lacked sensation, would soon be destroyed, and would never attain its end, which is the purpose of Nature. For how would it be nourished? Immobile animals indeed find nourishment in that out of which they are produced. §§ 851-3

             But a body, generated, not stationary, cannot possess a soul and intellectual discernment and yet not have sensation, (nor indeed can an ungenerated one). For why should it not have it? For the good [presumably] of either the soul or the body. But neither, surely. The soul would not think better nor the body benefit on that account. No animal then, whose body is mobile, lacks sensation.§§ 854-7

             But having sensation, a body must needs be either simple or compound. It cannot, however, be simple; for then it would lack touch, and it must have this sense.§ 858

             Which is evident from these considerations. Since an animal is an animate body, and every body is tangible, and the tangible is what is perceptible by touch, the animal's body must be able to touch if it is to survive. For the other senses perceive through an extraneous medium; e.g. smell, sight, hearing. But if the animal that comes into contact [with other things] had no sense of touch it could not avoid certain things and seize upon others; and thus it could not preserve its existence.§§ 859-60

             This is why taste is a kind of touch; for food is a tangible body. But sound and colour and smell do not nourish, or contribute to growth or decay. Taste must then be a kind of touch, being a sense of the tangible and the nutritive. These senses then are necessary to the animal. Hence it is plain that no animal can exist without touch.§ 861

             The others exist for its greater good; and then not in every kind of animal, but in some, namely in those that need to move from place to place. For if [such] an animal is to survive it must perceive not only what is in contact with it, but also what is afar; and this will happen, if it perceives through a medium, this being affected and moved by the sense object, and the animal itself by the medium.§ 862

             It is [as when] a thing is moving locally: it operates till it affects a change and, impelling something else, causes another impulsion, so that movement traverses a medium. The first mover causes motion and is unmoved: the last is moved, moving nothing else; but the intermediary is both; or the many intermediaries. So it is with the alteration in question, except that what is changed remains in the same place. If one dips an object into wax, the wax moves to the extent that the object enters it; whereas a stone is not moved at all; but water a long way, and air most of all, giving and receiving motion, so long as it remains a unity. Hence, as regards reflection, it is better to say that the air is affected by shape and colour, so long as it retains unity, than to say that the sight proceeds out and is reflected back. On a smooth surface [air] has unity, and so in turn, moves the sight; as if a seal were to sink into and right through wax.§§ 863-4