, neither are nor can
be anything but those precise abstract ideas we have in our minds. And
therefore the supposed real essences of substances, if different from
our abstract ideas, cannot be the essences of the species WE rank
things into. For two species may be one, as rationally as two different
essences be the essence of one species: and I demand what are the
alterations [which] may, or may not be made in a HORSE or LEAD, without
making either of them to be of another species? In determining the
species of things by OUR abstract ideas, this is easy to resolve: but if
any one will regulate himself herein by supposed REAL essences, he will
I suppose, be at a loss: and he will never be able to know when anything
precisely ceases to be of the species of a HORSE or LEAD.

14. Each distinct abstract Idea is a distinct Essence.

Nor will any one wonder that I say these essences, or abstract ideas
(which are the measures of name, and the boundaries of species) are
the workmanship of the understanding, who considers that at least the
complex ones are often, in several men, different collections of simple
ideas; and therefore that is COVETOUSNESS to one man, which is not so to
another. Nay, even in substances, where their abstract ideas seem to be
taken from the things themselves, they are not constantly the same; no,
not in that species which is most familiar to us, and with which we have
the most intimate acquaintance: it having been more than once doubted,
whether the FOETUS born of a woman were a MAN, even so far as that it
hath been debated, whether it were or were not to be nourished and
baptized: which could not be, if the abstract idea or essence to
which the name man belonged were of nature's making; and were not
the uncertain and various collection of simple ideas, which the
understanding put together, and then, abstracting it, affixed a name
to it. So that, in truth, every distinct abstract idea is a distinct
essence; and the names that stand for such distinct ideas are the
names of things essentially different. Thus a circle is as essentially
different from an oval as a sheep from a goat; and rain is as
essentially different from snow as water from earth: that abstract idea
which is the essence of one being impossible to be communicated to the
other. And thus any two abstract ideas, that in any part vary one
from another, with two distinct names annexed to them, constitute two
distinct sorts, or, if you please