PSYCHOLOGICAL SCIENCE Research Article THE IMPACT OF NECESSITY AND SUFFICIENCY IN THE WASON FOUR-CARD SELECTION TASK

Abstract—Performance in the Wason card selection task is often improved given thematic content. Such content effects have been con-sidered evidence against human rationality. We propose that the role of content lies in specifying premises underlying “if P, then Q ” rules. Unlike thematic rules, abstract conditional rules do not explicitly pro-vide material interpretation (P is a sufficient but not necessarily a nec-essary condition for Q), resulting in nonnormative responses. When necessity–sufficiency relations were explicated, normative responses were elicited and effects of other logically irrelevant components dis-appeared. The results suggest that content effects are compatible with human rationality. The question of whether human reasoning is based on formal logic-based, domain-general mechanisms or on pragmatic content-based, domain-specific mechanisms has served as the focus of a long-standing debate in psychology (e.g., Cheng & Holyoak, 1985; Henle