Deductive reasoning with factual, possible, and counterfactual conditionals

We compared reasoners' inferences from conditionals based on possibilities in the present or the past (e.g., "If Linda had been in Dublin then Cathy w ould have been in Galway") with their inferences based on facts in the pres ent or the past (e.g., "If Linda was in Dublin then Cathy was in Galway"). We propose that people construct a richer representation of conditionals th at deal with possibilities rather than facts: Their models make explicit no t only the suppositional case, in which Linda is in Dublin and Cathy is in Galway, but also the presupposed case, in which Linda is not in Dublin and Cathy is not in Galway., We report the results of four experiments that cor roborate this model theory. The experiments show that reasoners make more i nferences from conditionals based on possibilities rather than on facts whe n the inferences depend On the presupposed case. The results also show that reasoners generate different situations to verify and falsify conditionals based on possibilities and facts.