— 587 —
      §12. If this be so, it is not to be wondred, 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
— 588 —
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.
Locke Hum IV, 6, §12, pp. 587-588