"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 two states in respect of their priority of development in a particular person, we shall see that the state of latent possession comes first. We may therefore define the Soul or Vital principle as _The earliest {205} realisation (entelechy) of a natural body having in it the potentiality of life_.