But where the nominal essence is kept to, as the boundary of each species, and men extend the application of any general term no further than to the particular things in which the complex idea it stands for is to be found, there they are in no danger to mistake the bounds of each species, nor can be in doubt, on this account, whether any proposition be true or not.

I have chosen to explain this uncertainty of propositions in this scholastic way, and have made use of the terms of ESSENCES, and SPECIES, on purpose to show the absurdity and inconvenience there is to think of them as of any other sort of realities, than barely abstract ideas with names to them.
To suppose that the species of things are anything but the sorting of them under general names, according as they agree to several abstract ideas of which we make those names signs, is to confound truth, and introduce uncertainty into all general propositions that can be made about them.

Though therefore these things might, to people not possessed with scholastic learning, be treated of in a better and clearer way yet those wrong notions of essences or species having got root in most people's minds who have received any tincture from the learning which has prevailed in this part of the world, are to be discovered and removed, to make way for that use of words which should convey certainty with it.
5.

This more particularly concerns Substances.
The names of substances, then, whenever made to stand for species which are supposed to be constituted by real essences which we know not, are not capable to convey certainty to the understanding.

Of the truth general propositions made up of such terms we cannot be sure.