Proceedings of the Annual Meeting of the Cognitive Science Society

Hypothetical reasoning - thinking about what might happen in the future or what might have happened in the past - enables us to go beyond factual reality. W e suggest that human reasoners construct a more explicit mental representation of hypothetical conditionals, such as. If Linda were in Dublin then Cathy would be in Galway, than of factual conditionals, such as, if Linda is in Dublin then Cathy is in Galway. When people think about the factual conditional, they keep in mind the affirmative situation -- Linda is in DubUn, Cathy is in Galway, and they maintain only an implicit awareness that there may be alternatives to this situation. In contrast, when they think about the hypothetical conditional, they keep in mind not only the affirmative situation, but also the presupposed negative one (Linda is not in Dublin, Cathy is not in Galway). The postulated differences in mental representations lead us to expect differences in the frequency of inferences that people make from the two sorts of conditionals, and we report the results of an experiment that corroborates this prediction. The psychological data have implications for philosophical and linguistic accounts of counterfactual conditionals, and for artificial intelligence programs designed to reason hypothetically.