Evidence for the Theory: Predicting the Difficulty of Propositional Logic Inference Problems

There has long been a controversy about the relation of logic to the ordinary deductive reasoning of subjects untutored in logic. Twentieth century philosophy has generally held that logic has only a normative relation to reasoning (e.g., Cohen, 1944): Logic specifies the correct responses but says nothing about how they are achieved. From a psychological standpoint, however, it is often hard to explain correct responses if one cannot assume that the reasoner is following logical principles.