1. imagining ways in which events in one’s life might have turned out differently. This often involves feelings of regret or disappointment (e.g., If only I hadn’t been so hasty) but may also involve a sense of relief, as at a narrow escape (e.g., If I had been standing three feet to the left…).

2. any process of reasoning based on a conditional statement of the type “If X, then Y” where X is known to be contrary to fact, impossible, or incapable of empirical verification. Counterfactual thinking of the first sort is common in such historical speculations as If Hitler had been killed in July 1944, then … . Counterfactual thinking of the second and third types can play a useful role in evaluating the implications of a theory or heuristic and in thought experiments. See also as-if hypothesis; conditional reasoning.