istotle's treatise on the subject (_De Anima_,
ii. p. 1) in which this fundamental conception of Aristotle's
philosophy is very completely illustrated:--

"Now as to Substance we remark that this is one particular category
among existences, having three different aspects. First there is, so
to say, the raw material or Matter, having in it no definite character
or quality; next the Form or Specific character, in virtue of which the
thing becomes namable; and third, there is the Thing or Substance which
these two together constitute. The Matter is, in other words, the
_potentiality_ of the thing, the Form is the _realisation_ of that
potentiality. We may further have this realisation in two ways,
corresponding in character to the distinction between _knowledge_
(which we have but are not necessarily using) and actual
_contemplation_ or mental perception.

"Among substances as above defined those are most truly such which we
call _bodily objects_, and among these most especially objects which
are the products of nature, inasmuch as all other bodies must be
derived from them. Now among such natural objects some are possessed
of life, some are not; by _life_ I mean a process of spontaneous
nourishment, growth, and decay. Every natural {204} object having life
is a substance compounded, so to say, of several qualities. It is, in
fact, a bodily substance defined in virtue of its having life. Between
the living body thus defined and the Soul or Vital principle, a marked
distinction must be drawn. The body cannot be said to 'subsist in'
something else; rather must we say that it is the matter or substratum
in which something else subsists. And what we mean by the soul is just
this substance in the sense of the _form_ or specific character that
subsists in the natural body which is _potentially_ living. In other
words, the Soul is substance as _realisation_, only, however, of such a
body as has just been defined. Recalling now the distinction between
realisation as possessed knowledge and as actual contemplation, we
shall see that in its essential nature the Soul or Vital principle
corresponds rather with the first than with the second. For both sleep
and waking depend on the Soul or Life being there, but of these waking
only can be said to correspond with the active form of knowledge; sleep
is rather to be compared with the state of having without being
immediately conscious that we have. Now if we compare these tw