We discuss two different kinds of thinking about what might have been: Counterfactual "if only" thinking about how things might have been different and semifactual "even if" thinking about how things might have tumed out the same. We report the results of an experiment that showed that the two kinds of thinking have different effects on cause and emotion judgements. The experiment provides the first demonstration that semifactual "even if" thoughts reduce peoples judgements of causality and their emotional reactions compared to no thoughts about what might have been, and it replicates recent findings that counterfactual "if only" thoughts increase peoples judgements of causality and their emotional reactions.

Reasoning about matters of tact and reasoning about matters of possibility and impossibility may depend on the same sorts of mental representations and processes. We illustrate a mental model theory of counterfactual thinking with reference to the action effect (the tendency to regret actions more than inactions) and we describe an experiment which examines the effects of short-term and long-term perspectives on regret for actions and inactions.

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.