6. Even the real essences of individual substances imply potential sorts.
It is true, I have often mentioned a real
essence distinct in substances from those abstract ideas of them, which I call their nominal essence. By this real
essence I mean, that real constitution of anything, which is the foundation of all those properties that are
combined in, and are constantly found to co-exist with the nominal essence; that particular constitution which
everything has within itself, without any relation to anything without it. But essence, even in this sense, relates to
a sort, and supposes a species. For, being that real constitution on which the properties depend, it necessarily
supposes a sort of things, properties belonging only to species, and not to individuals: v.g. supposing the nominal
essence of gold to be a body of such a peculiar colour and weight, with malleability and fusibility, the real essence
is that constitution of the parts of matter on which these qualities and their union depend; and is also the
foundation of its solubility in aqua regia and other properties, accompanying that complex idea. Here are essences
and properties, but all upon supposition of a sort or general abstract idea, which is considered as immutable; but
there is no individual parcel of matter to which any of these qualities are so annexed as to be essential to it or
inseparable from it. That which is essential belongs to it as a condition whereby it is of this or that sort: but take
away the consideration of its being ranked under the name of some abstract idea, and then there is nothing
necessary to it, nothing inseparable from it. Indeed, as to the real essences of substances, we only suppose their
being, without precisely knowing what they are; but that which annexes them still to the species is the nominal
essence, of which they are the supposed foundation and cause.