This supposition, however, that the same precise and internal constitution goes always with the same specific name, makes men forward to take those names for the representatives of those real essences; though indeed they signify nothing but the complex ideas they have in their minds when they use them.

So that, if I may so say, signifying one thing, and being supposed for, or put in the place of another, they cannot but, in such a kind of use, cause a great deal of uncertainty in men's discourses; especially in those who have thoroughly imbibed the doctrine of SUBSTANTIAL FORMS, whereby they firmly imagine the several species of things to be determined and distinguished.
21.

This Abuse contains two false Suppositions.
But however preposterous and absurd it be to make our names stand for ideas we have not, or (which is all one) essences that we know not, it being in effect to make our words the signs of nothing; yet it is evident to any one who ever so little reflects on the use men make of their words, that there is nothing more familiar.

When a man asks whether this or that thing he sees, let it be a drill, or a monstrous foetus, be a MAN or no; it is evident the question is not, Whether that particular thing agree to his complex idea expressed by the name man: but whether it has in it the real essence of a species of things which he supposes his name man to stand for.

In which way of using the names of substances, there are these false suppositions contained:-- First, that there are certain precise essences according to which nature makes all particular things, and by which they are distinguished into species.