19. Our nominal essences of substances not perfect collections of the properties that flow from their real essences.
Fifthly, The only imaginable help in this case would be, that, having framed perfect complex ideas of the
properties of things flowing from their different real essences, we should thereby distinguish them into species.
But neither can this be done. For, being ignorant of the real essence itself, it is impossible to know all those
properties that flow from it, and are so annexed to it, that any one of them being away, we may certainly conclude
that that essence is not there, and so the thing is not of that species. We can never know what is the precise
number of properties depending on the real essence of gold, any one of which failing, the real essence of gold, and
consequently gold, would not be there, unless we knew the real essence of gold itself, and by that determined that
species. By the word gold here, I must be understood to design a particular piece of matter; v.g. the last guinea
that was coined. For, if it should stand here, in its ordinary signification, for that complex idea which I or any one
else calls gold, i.e., for the nominal essence of gold, it would be jargon. So hard is it to show the various meaning
and imperfection of words, when we have nothing else but words to do it by.
