15. Knowledge not always clear, where the ideas that enter into it are clear.
But since our knowledge is founded
on and employed about our ideas only, will it not follow from thence that it is conformable to our ideas; and that
where our ideas are clear and distinct, or obscure and confused, our knowledge will be so too? To which I answer,
No: for our knowledge consisting in the perception of the agreement or disagreement of any two ideas, its
clearness or obscurity consists in the clearness or obscurity of that perception, and not in the clearness or
obscurity of the ideas themselves: v.g. a man that has as clear ideas of the angles of a triangle, and of equality to
two right ones, as any mathematician in the world, may yet have but a very obscure perception of their agreement,
and so have but a very obscure knowledge of it. But ideas which, by reason of their obscurity or otherwise, are
confused, cannot produce any clear or distinct knowledge; because, as far as any ideas are confused, so far the
mind cannot perceive clearly whether they agree or disagree. Or to express the same thing in a way less apt to be
misunderstood: he that hath not determined ideas to the words he uses, cannot make propositions of them of
whose truth he can be certain.
