take not, two opinions. The one is of those
who, using the word essence for they know not what, suppose a certain
number of those essences, according to which all natural things are
made, and wherein they do exactly every one of them partake, and so
become of this or that species. The other and more rational opinion is
of those who look on all natural things to have a real, but unknown,
constitution of their insensible parts; from which flow those sensible
qualities which serve us to distinguish them one from another, according
as we have occasion to rank them into sorts, under common denominations.
The former of these opinions, which supposes these essences as a certain
number of forms or moulds, wherein all natural things that exist are
cast, and do equally partake, has, I imagine, very much perplexed the
knowledge of natural things. The frequent productions of monsters, in
all the species of animals, and of changelings, and other strange issues
of human birth, carry with them difficulties, not possible to consist
with this hypothesis; since it is as impossible that two things
partaking exactly of the same real essence should have different
properties, as that two figures partaking of the same real essence of a
circle should have different properties. But were there no other reason
against it, yet the supposition of essences that cannot be known; and
the making of them, nevertheless, to be that which distinguishes the
species of things, is so wholly useless and unserviceable to any part of
our knowledge, that that alone were sufficient to make us lay it by, and
content ourselves with such essences of the sorts or species of things
as come within the reach of our knowledge: which, when seriously
considered, will be found, as I have said, to be nothing else but, those
ABSTRACT complex ideas to which we have annexed distinct general names.

18. Real and nominal Essence

Essences being thus distinguished into nominal and real, we may further
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
itself; that foundation from which all its properties flow, and to which
they are all inseparably annexed. But it is far otherwise conce