Proceedings of the Annual Meeting of the Cognitive Science Society

Reasoning about possibilities is fundamental in daily life and inartificial intelligence. It is formalized in modal logics, of whichthere are infinitely many. Two experiments showed thatindividuals make inferences that are parsimonious aboutpossibilities, and that they reject conclusions referring topossibilities that the premises do not support. Both sorts ofinference contravene modal logics, i.e., the simplest system ofmodal logic and the infinite number of systems based on it.