Reviewing Richard Evans’ Altered Pasts: Counterfactuals in History, Cass Sunstein argues that what-if scenarios aren’t, as E. P. Thompson put it, “unhistorical shit,” but rather an integral part of the historical enterprise:
Here is another way to make the point. Social scientists test hypotheses. They might hypothesize, for example, that if people have to pay a small tax for plastic bags at convenience stores, they will use fewer plastic bags. To test hypotheses, social scientists usually like to conduct randomized controlled trials, allowing them to isolate the effects of the tax. Such trials create parallel worlds and hence alternative histories—one with the tax and one without it.
Historians cannot conduct randomized controlled trials, because history is run only once. Yet they nonetheless develop hypotheses, and they attempt to evaluate them by reference to the evidence. Evans is himself engaged in this enterprise. There is no difference between hypothesis-testing and counterfactual inferences. Any claim of causation, resulting from such tests, requires a statement that without the cause, the effect would not have occurred.
Evans appreciates the entertainment value of the most imaginative counterfactual narratives, but he doesn’t want them to be taken seriously, or to be seen as what historians do. With Thompson and Oakeshott (and countless others), he thinks that historians should explain what did happen, not what didn’t happen. The problem is that, to offer an explanation of what happened, historians have to identify causes, and whenever they identify causes they immediately conjure up a counterfactual history, a parallel world. Sure, there is a lot of distance between science fiction novelists and the world’s great historians, but along an important dimension they are playing the same game.