CHAPTER II

THE DEFINITION JUSTIFIED

MODES OF LIFE

             SINCE it is from the less clear, though more obvious, facts that what is certain and more evident to thought emerges, let us attempt to approach the matter afresh.§ 245

             For it is not enough that a defining principle should merely show a fact, as do most formulae, but also there should be contained and made plain the causes involved. Usually the constituent terms are like conclusions: for instance, what is a square, that is equal to an oblong? An equilateral orthogon. Such a term is of the nature of a conclusion. But to say that a square is the discovery of a mean line states the reason why.§§ 246-52

             Going back, then, to the beginning of our enquiry, let us say that the animate is distinguished from the inanimate by being alive.

             To live, however, is predicated in several ways; and even if one only of these is present, we say there is life; as, for example, intellection, sensation, or movement and rest in place; as well as the movement and rest involved in nourishment, and growth and decay.§§ 253-5

             Hence all plants seem to live. They appear to have in themselves a power and principle of this kind, by which they increase or decay in various directions--that is to say, they do not grow up but not down, but alike either way; and in all their parts they are continually nourished, and they live so long as they can take nourishment.§§ 256-7

             It is possible for this power to exist apart from the others; but for the others to exist apart from it is impossible, at least in mortal beings. This is evident in plants; for there is in them no other soul-power. To live by this principle, then, is common to all living things.§ 258

             But an animal is such primarily by sensation. For we also call animals things that do not move or change their place, provided they have sensation, and do not merely live. There seem to be many of this sort: by nature they stay in one place, but they have one of the senses. 259

             Touch is in all, primarily. As the vegetative powers can be separated from touch and all sensation as a whole, so can touch from the other senses. (We give the name 'vegetative' to that part of the soul in which plants participate). All animals are seen to possess the sense of touch.§ 260

             For what cause each of these facts is so we shall say later on. At present only this need be said: that soul is the principle of the qualities we have discussed, and is characterised by the vegetative, sensitive, intellective and motive powers.§ 261