ON THESOUL(BOOKII) 159
For the defining statement not only needs to make clear what something is, as most
definitions do, but also needs to include and display the cause. As it is, the statements of
definitions are like conclusions. For example, what is squaring? The equality of an equi-
lateral rectangle to an oblong rectangle. But this sort of definition is a statement of the
conclusion, while one who says that squaring is the finding of a mean proportional
states the cause of the thing.
So we say, taking this as a starting point for the inquiry, that what is ensouled is
distinguished from what is soulless by living. But living is meant in more than one way,
and if any one alone of the following is present in something, we say it is alive: intellect,
perception, moving and stopping with respect to place, and the motion that results from
nourishment, that is, wasting away as well as growing. And for this reason all plants
seem to be alive, since they evidently have in themselves this sort of power and source,
through which they have growth and decay in opposite directions, for they do not just
grow upward but not downward, but in both directions alike, and in every direction, all
of them that are continually nourished and live for the sake of their ends, so long as they
are able to get food. The latter capacity can be present in separation from the others, but
the others cannot be present in separation from it in mortal beings. This is obvious in the
case of plants, since no other potency of soul belongs to them.
Life belongs to living things, then, through this source, but to an animal, first of
all, through sense perception; for even those that do not move or change their places, if
they have perception, we call animals and do not merely say they are alive. Now of per-
ception, the kind that first belongs to them all is touch, and just as the nutritive power is
able to be present separately from touch and all sense perception, so is touch able to be
present separately from the other senses. (By the nutritive power, we mean the part of
the soul of which the plants have a share; and it is obvious that animals all have the
sense of touch.) Through what cause each of these things happens, we will say later. For
now, let us say this much only, that the soul is the source of these things that have been
mentioned and is defined by them: by nutrition, by sense perception, by thinking things
through, and by motion.
Whether each of these is a soul or part of a soul, and if a part, whether in such a
way as to be separated only in speech or also in place, is for some of these not difficult
to see, but some present an impasse. For just as in the case of plants, some parts obvi-
ously live when divided and separated from each other, as though the soul in them is
one in each plant in the sense of being-at-work-staying-itself but is in potency more
than one, so too we see it happen with other capacities of the soul in the case of insects
that have been cut in half; for each of the two parts even has both perception and motion
with respect to place, and if it has perception, also imagination and appetite, since
where there is perception there is also pain and pleasure, and where these are there is
necessarily also desire. But about the intellect, that is, the contemplative faculty, noth-
ing is yet clear, but it seems that it is a distinct class of soul and that it alone admits of
being separated from body, as the everlasting from the destructible. As for the remain-
ing parts of the soul, it is clear from what has been said that they cannot be separate, as
some people say, though it is obvious that they are distinct in speech. For being percep-
tive is different from being capable of having opinion, if perceiving is also different
from having opinion, and similarly with each of the other parts mentioned. Further,
some animals have all these capacities, others some of them, and still others only one
(and this makes the difference among animals); why this is so must be considered later.
And it turns out much the same with the senses, since some animals have them all,
others some of them, and still others the one that is most necessary, touch.
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