The impact of necessity and sufficiency in the Wason four-card selection task

Performance in the Wason card selection task is often improved given themat ic content. Such content effects have been considered evidence against huma n rationality. We propose that the role of content lies in specifying premi ses underlying "if P, then Q" rules. Unlike thematic rules, abstract condit ional rules do not explicitly provide material interpretation (P is a suffi cient but not necessarily a necessary condition for Q), resulting in nonnor mative responses. When necessity-sufficiency relations were explicated, nor mative responses were elicited and effects of other logically irrelevant co mponents disappeared. The results suggest that content effects are compatib le with human rationality.