It is possible that some logician may not know that a and b exist, not know what they denote, and whether they are true or untrue. But virtually every logician will agree that the expression a ⊃ b cannot be true in a case in which a is true and b is false. Truth relationships thus understood — inasmuch as they are not specific to any particular field of science — are generally regarded as the proper concern of logic. Only (...) their study can uncover the typically human capacity to derive one piece of knowledge from another without referring back directly to objective reality. (shrink)