12. Our nominal essences of substances furnish few universal propositions about them that are certain.
If this be
so, it is not to be wondered that we have very imperfect ideas of substances, and that the real essences, on which
depend their properties and operations, are unknown to us. We cannot discover so much as that size, figure, and
texture of their minute and active parts, which is really in them; much less the different motions and impulses
made in and upon them by bodies from without, upon which depends, and by which is formed the greatest and
most remarkable part of those qualities we observe in them, and of which our complex ideas of them are made up.
This consideration alone is enough to put an end to all our hopes of ever having the ideas of their real essences;
which whilst we want, the nominal essences we make use of instead of them will be able to furnish us but very
sparingly with any general knowledge, or universal propositions capable of real certainty.
