Proceedings of the Annual Meeting of the Cognitive Science Society

People reason about possibilities routinely, and reasoners caninfer “modal” conclusions, i.e., conclusions that concern whatis possible or necessary, from premises that make no mentionof modality. For instance, given that Cullen was born in NewYork or Kentucky, it is intuitive to infer that it’s possible thatCullen was born in New York, and a recent set of studies onmodal reasoning bear out these intuitions (Hinterecker,Knauff, & Johnson-Laird, 2016). What explains the tendencyto make modal inferences? Conventional logic does not applyto modal reasoning, and so logicians invented manyalternative systems of modal logic to capture valid modalinferences. But, none of those systems can explain theinference above. We posit a novel theory based on the ideathat reasoners build mental models, i.e., iconic simulations ofpossibilities, when they reason about sentential connectivessuch as and, if, and or (Johnson-Laird, 2006). The theoryposits that reasoners represent a set of conjunctivepossibilities to capture the meanings of compound assertions.It is implemented in a new computational process model ofsentential reasoning that can draw modal conclusions fromnon-modal premises. We describe the theory andcomputational model, and show how its performance matchesreasoners’ inferences in two studies by Hinterecker et al.(2016). We conclude by discussing the model-based theory inlight of alternative accounts of reasoning.