Title: The Semantics and Psychology of Negation: the Australian plan, Negation as failure, and card selection tasks

Abstract: In this talk, I will explain how two different kinds of semantics for negation can be used to help us understand some puzzles in the psychology of reasoning. I introduce the “Australian Plan” semantics for negation, which generalises the semantics of negation as found in “worlds” semantics for intuitionistic logic, relevant logics and other substructural logics; and semantics from logic programming and default logic which treat negation as failure. I provide a framework in which two kinds of semantic clauses for negation coexist, and use this to model to give a possible account of why reasoners fare differently in card selection tasks depending on whether the target property is phrased positively or negatively. (This is joint work with Francesco Berto.)