— 417 —
Real and nominal Essence.       §15. But since the Essences of Things are Thought, by some, (and
not without reason,) to be wholly unknown; it may not be amiss to
consider the several significations of the Word Essence.
First, Essence may be taken for the very being of any thing, where-
by it is, what it is. And thus the real internal, but generally in
Substances, unknown Constitution of Things, whereon their dis-
coverable Qualities depend, may be called their Essence. This is the
proper original signification of the Word, as is evident from the
formation of it; Essentia, in its primary notation signifying properly
Being. And in this sense it is still used, when we speak of the
Essence of particular things, without giving them any Name.
Secondly, The Learning and Disputes of the Schools, having been
much busied about Genus and Species, the Word Essence has almost
lost its primary signification; and instead of the real Constitution of
things, has been almost wholly applied to the artificial Constitution
of Genus and Species. ’Tis true, there is ordinarily supposed a real
Constitution of the sorts of Things; and ’tis past doubt, there must
be some real Constitution, on which any Collection of simple Ideas
co-existing, must depend. But it being evident, that Things are
ranked under Names into sorts or Species, only as they agree to
certain abstract Ideas, to which we have annexed those Names, the
Essence of each Genus, or Sort, comes to be nothing but that abstract
Idea, which the General, or Sortal (if I may have leave so to call it
from Sort, as I do General from Genus,) Name stands for. And this we
shall find to be that, which the Word Essence imports, in its most
familiar use. These two sorts of Essences, I suppose, may not unfitly
be termed, the one the Real, the other the Nominal Essence.
Locke Hum III, 3, §15, p. 417