2. The essence of each sort of substance is our abstract idea to which the name is annexed.
The measure and
boundary of each sort or species, whereby it is constituted that particular sort, and distinguished from others, is
that we call its essence, which is nothing but that abstract idea to which the name is annexed; so that everything
contained in that idea is essential to that sort. This, though it be all the essence of natural substances that we know,
or by which we distinguish them into sorts, yet I call it by a peculiar name, the nominal essence, to distinguish it
from the real constitution of substances, upon which depends this nominal essence, and all the properties of that
sort; which, therefore, as has been said, may be called the real essence: v.g. the nominal essence of gold is that
complex idea the word gold stands for, let it be, for instance, a body yellow, of a certain weight, malleable,
fusible, and fixed. But the real essence is the constitution of the insensible parts of that body, on which those
qualities and all the other properties of gold depend. How far these two are different, though they are both called
essence, is obvious at first sight to discover.