He finds (ch., ii) that Knowledge is either an intuitive, a demonstrative, or a sensuous perception of absolute certainty, in regard to one or other of four sorts of agreement or disagreement on the part of ideas: of each idea with itself, as identical, and different from every other; in their abstract relations to one another; in their necessary connexions, as qualities and powers coexisting in concrete substances; and as revelations to us of the final realities of existence.