ration, that the three
angles of a triangle are equal to two right ones, what do we more but
perceive, that equality to two right ones does necessarily agree to, and
is inseparable from, the three angles of a triangle?

3. This Agreement or Disagreement may be any of four sorts.

But to understand a little more distinctly wherein this agreement or
disagreement consists, I think we may reduce it all to these four sorts:

I. IDENTITY, or DIVERSITY. II. RELATION. III. CO-EXISTENCE, or NECESSARY
CONNEXION. IV. REAL EXISTENCE.

4. First, Of Identity, or Diversity in ideas.

FIRST, As to the first sort of agreement or disagreement, viz. IDENTITY
or DIVERSITY. It is the first act of the mind, when it has any
sentiments or ideas at all, to perceive its ideas; and so far as it
perceives 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 itself, 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 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 agreement 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, it will always be found to
be about the names, and not the ideas themselves, whose identity and
diversity will always be perceived, as soon and clearly as the ideas
themselves are; nor can it possibly be otherwise.

5. Secondly, Of abstract Relations between ideas.

SECONDLY, the next sort of agreem