Real essences.

First, Essence may be taken for the very being of anything, whereby it
is what it is. And thus the real internal, but generally (in substances)
unknown constitution of things, whereon their discoverable qualities
depend, may be called their essence. This is the proper original
signification of the word, as is evident from the formation of it;
essential 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.

Nominal Essences.

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. It is true, there is ordinarily supposed a real
constitution of the sorts of things; and it is 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