articular virtue or vice, that I am able to form
an idea of that particular virtue or vice. If so, I admit that my idea
of that particular virtue or vice is but, as Hume would say, a copy of
my feeling. And since, undoubtedly, I can feel myself thinking, or
perceiving, or performing any other mental operation, I am bound to
admit, further, that my idea of any such operation may equally be
described as a copy of a sensation which I have experienced. All I
contend for is that if, after having formed my idea, either of a mental
operation or of anything else whatever, I proceed to ask myself what
sort of an entity that idea is, the answer which I give myself, or, in
other words, the idea which I form of my previous idea, being a copy of
idea, cannot be a copy of sensation.

So much must surely be conceded to me, for that white, being white,
cannot be also black is not nearly so certain as that idea and
sensation, being two distinct things, idea of idea cannot be idea of
sensation. The concession, indeed, is likely enough to be accompanied by
an exclamation of wonder that so microscopic a flaw in an elaborate
exposition should be thought worth pointing out; but Hume himself would
certainly not have so retorted. Of the doctrine which I am impugning,
viz., that every _idea_ is copied from some preceding _sensation_, he
had spoken as follows:--'Those who would assert that this position is
not universally true, nor without exception, have only one, and that an
easy, method of refuting it, by producing the idea which, in their
opinion, is not derived from this source. It will then be incumbent on
us, if we would maintain our doctrine, to produce the impression or
lively perception which corresponds to it.' He was much too candid not
to have acknowledged that this challenge of his had been fairly and
fully met. He was not a man to refuse to own himself refuted when, after
distinctly intimating that the production of one single idea, having no
perception correspondent to it amongst those which we experience 'when
we see, or hear, or feel, or love, or hate, or will, or desire,' would
suffice for his entire refutation, he found such an idea produced. He
knew too well also to what enormous errors of thought minute errors of
expression may lead, to disregard any speck of inaccuracy in any one of
his definitions. The apparently slight oversight committed by him on
this occasion will, indeed, be presently seen to have sensibly
contribute