Logic, assuming certain principles to be true of experience, or at least to be conditions of consistent discourse, distinguishes the kinds of propositions that can be shown to agree with these principles, and explains by what means the agreement can best be exhibited.

Such principles are those of Contradiction (chap.
vi.), the Syllogism (chap.

ix.), Causation (chap.

xiv.), and Probabilities (chap.

xx.).