The role of contradictions and counterexamples in the rejection of false sentences

Abstract

Two hypotheses about the processes by which people can reject false but meaningful sentences quantified by all or some are outlined. These hypotheses distinguish between two basic types of false sentences: contradictory sentences (e.g., All/Some birds are dogs), which are rejected on the basis of a direct contradiction between the subject and predicate concepts; and counterexample sentences (e.g., All birds are robins), which are falsified when the person thinks of a counterexample to the assertion (e.g., canary). Experiment I demonstrated that people use contradictions to produce false completions of sentences. In Experiment II, the false production frequency norms obtained in Experiment I, together with the theoretical analysis of false sentences, were used to predict the time required to reject false sentences. The results supported the contradiction and counterexample hypotheses, and indicated that false sentences with subject and predicate words closely related in meaning can sometimes be disconfirmed relatively quickly. Experiment III extended the counterexample hypothesis to sentences containing the verb have (e.g., All buildings have elevators), and also provided some evidence that the process of exemplar search used to find counterexamples may also sometimes play a role in the verification of true generalizations.