— 525 —
First, of Identity or Diversity.
      §4. First, As to the first sort of Agreement or Disagreement, viz.
Identity, or Diversity. ’Tis the first Act of the Mind, when it has any
— 526 —
Sentiments or Ideas at all, to perceive its Ideas, and so far as it per-
ceives them, to know each what it is, and thereby also to perceive
their difference, and that one is not another. This is so absolutely
necessary, that without it there could be no Knowledge, no
Reasoning, no Imagination, no distinct Thoughts at all. By this
the Mind clearly and infallibly perceives each Idea to agree with it
self, and to be what it is; and all distinct Ideas to disagree, i.e. the
one not to be the other: And this it does without any pains, labour,
or deduction; but at first view, by its natural power of Perception
and Distinction. And though Men of Art have reduced this into
those general Rules, What is, is; and it is impossible for the same thing to
be, and not to be, for ready application in all cases, wherein there may
be occasion to reflect on it; yet it is certain, that the first exercise of
this Faculty, is about particular Ideas. A Man infallibly knows, as
soon as ever he has them in his Mind that the Ideas he calls White
and Round, are the very Ideas they are, and that they are not other
Ideas which he calls Red or Square. Nor can any Maxim or Proposition
in the World make him know it clearer or surer than he did before,
and without any such general Rule. This then is the first agree-
ment, or disagreement, which the Mind perceives in its Ideas;
which it always perceives at first sight: And if there ever happen
any doubt about it, ’twill always be found to be about the Names,
and not the Ideas themselves, whose Identity and Diversity will
always be perceived, as soon and as clearly as the Ideas themselves
are, nor can it possibly be otherwise.
Locke Hum IV, 1, §4, pp. 525-526