— 383 —
Ideas of Substances are ἔκτυπα, inadequate.       §13. Secondly, The complex Ideas of Substances are Ectypes, Copies
too; but not perfect ones, not adequate: which is very evident to the
Mind, in that it plainly perceives, that whatever Collection of
simple Ideas it makes of any Substance that exists, it cannot be
sure, that it exactly answers all that are in that Substance. Since
not having tried all the Operations of all other Substances upon it,
and found all the Alterations it would receive from, or cause in
other Substances, it cannot have an exact adequate Collection of
all its active and passive Capacities; and so not have an adequate
complex Idea of the Powers of any Substance, existing, and its
Relations, which is that sort of complex Idea of Substances we have.
And, after all, if we could have, and actually had, in our complex
Idea, an exact Collection of all the secondary Qualities, or Powers
of any Substance, we should not yet thereby have an Idea of the
Essence of that Thing. For since the Powers, or Qualities, that are
observable by us, are not the real Essence of that Substance, but
depend on it, and flow from it, any Collection whatsoever of these
Qualities, cannot be the real Essence of that Thing. Whereby it is
plain, that our Ideas of Substances are not adequate; are not what the
Mind intends them to be. Besides, a Man has no Idea of Substance
in general, nor knows what Substance is in it self.
Locke Hum II, 31, §13, p. 383