Philosophers and historians have long been suspicious of modal and counterfactual claims. I argue, however, that historians often legitimately use modal and counterfactual claims for a variety of purposes. They help identify causes, and hence help explain events in history. They are used to defend judgments about people, and to highlight the importance of particular events. I defend these uses of modal claims against two arguments often used to criticize modal reasoning, using the philosophy of science to ground the truth (...) of modal claims. This analysis puts several important points into perspective, including how certain we can be about our claims about what might have been, and the role that determinism plays in those claims. The proper analysis of modality shows, I argue, that counterfactual claims are legitimate and important, if often uncertain, and that issues of determinism are irrelevant to the modal claims used in historical analysis. (shrink)