— 418 —
Real and nominal Essence the same in simple Ideas and Modes, different in Substances.       §18. Essences being thus distinguished into Nominal and Real, we
may farther observe, that in the Species of simple Ideas and Modes,
they are always the same: But in Substances, always quite different. Thus a
Figure including a Space between three Lines, is the real, as well as
nominal Essence of a Triangle; it being not only the abstract Idea to
which the general Name is annexed, but the very Essentia, or Being,
of the thing it self, that Foundation from which all its Properties
flow, and to which they are all inseparably annexed. But it is far
— 419 —
otherwise concerning that parcel of Matter, which makes the Ring
on my Finger, wherein these two Essences are apparently different.
For it is the real Constitution of its insensible Parts, on which
depend all those properties of Colour, Weight, Fusibility, Fixedness,
etc. which are to be found in it. Which Constitution we know not;
and so having no particular Idea of, have no Name that is the Sign
of it. But yet it is its Colour, Weight, Fusibility, and Fixedness, etc.
which makes it to be Gold, or gives it a right to that Name, which is
therefore its nominal Essence. Since nothing can be call’d Gold, but
what has a Conformity of Qualities to that abstract complex Idea,
to which that Name is annexed. But this Distinction of Essences,
belonging particularly to Substances, we shall, when we come to
consider their Names, have an occasion to treat of more fully.
Locke Hum III, 3, §18, pp. 418-419