On The Soul
a mean proportional between the two unequal sides of the given
rectangle discloses the ground of what is defined.
We resume our inquiry from a fresh starting-point by calling
attention to the fact that what has soul in it differs from what has
not, in that the former displays life. Now this word has more than one
sense, and provided any one alone of these is found in a thing we
say that thing is living. Living, that is, may mean thinking or
perception or local movement and rest, or movement in the sense of
nutrition, decay and growth. Hence we think of plants also as
living, for they are observed to possess in themselves an
originative power through which they increase or decrease in all
spatial directions; they grow up and down, and everything that grows
increases its bulk alike in both directions or indeed in all, and
continues to live so long as it can absorb nutriment.
This power of self-nutrition can be isolated from the other powers
mentioned, but not they from it-in mortal beings at least. The fact is
obvious in plants; for it is the only psychic power they possess.
This is the originative power the possession of which leads us to
speak of things as living at all, but it is the possession of
sensation that leads us for the first time to speak of living things
as animals; for even those beings which possess no power of local
movement but do possess the power of sensation we call animals and not
merely living things.
The primary form of sense is touch, which belongs to all animals.
just as the power of self-nutrition can be isolated from touch and
sensation generally, so touch can be isolated from all other forms
of sense. (By the power of self-nutrition we mean that departmental
power of the soul which is common to plants and animals: all animals
whatsoever are observed to have the sense of touch.) What the
explanation of these two facts is, we must discuss later. At present
we must confine ourselves to saying that soul is the source of these
phenomena and is characterized by them, viz. by the powers of