To begin with, let’s set aside some of the reasons why historians have dismissed counterfactuals in the past. We need not, for instance, pay too much attention to the attachment of Marxists (like Carr) and Hegelian idealists (like Oakeshott) to teleological history. Of course, if history represents the unfolding of a dialectical process, then events that did not occur cannot, by definition, constitute the subject of historical analysis. Crude Marxism (and Hegelianism) is, I hope, still out of favor. But another reason why historians are skeptical of the counterfactual seems better grounded. And this is historians’ attachment to the factual.

Consider, Niall Ferguson’s edited volume Virtual History. It provides an excellent defense of counterfactual history. The counterfactuals considered by Ferguson and co, however, are largely in military or diplomatic history: what would have happened had the Nazis’ invaded Britain? etc.

These counterfactuals are a useful way to think through a question. But their power typically depends on reversing a single decision or event, i.e. suppose Hitler doesn’t issue his Stop Order in June 1940 or Edward Grey decides not to defend Belgium neutrality, what then? To be plausible everything else has to be held constant. This means that counterfactuals in diplomatic and military history shed light on the short term consequences of particular events. But the ceteris paribus assumption becomes harder to maintain as we consider events further removed from the initial counterfactual intervention. Thus, we have a reasonable idea of what Nazi rule of Britain in 1940 might have looked like — with the SS hunting down Jews, liberals, and intellectuals and restoring Edward VIII to the throne. But once we consider the outcomes of a Nazi ruled Britain into the 1950s and 1960s, we have much less guidance. Lacking any documentary evidence of the intentions of Britain’s Nazi rulers in the post-war era leaves us in the realm of historical fiction like Robert Harris’ Fatherland or CJ Sansom’s Dominion; there are simply too many degrees of freedom to do conduct historical analysis. Counterfactuals become problematic once we run out of facts to discipline our analysis.

This is the one fact it a valid reason for historians to be skeptical of counterfactuals. The actual historical record has to serve as a constant constraint on historical writing. This goes back to Leopold von Ranke, the scholar responsible for history’s emergence as an academic discipline in the 19th century. Ranke and his followers insisted on rigorous documentation and established the idea that the craft of the historian lay in the discovery, assembly, and analysis of primary sources. Ranke urged historians to focus on what actually happened; simply put, the facts ma’am, just the facts. Many criticisms have been levied at Ranke in the intervening 150 years, and to jaded post-modern eyes this approach no doubt appears hopeless naïve. But we should not dismiss Ranke’s strictures too quickly given what happens when historians abandon them (here and here). What is important here is that the same Rankian strictures that helped form history as an academic discipline, also rule out speculating about things that didn’t happen. They instill in historians a natural skepticism of counterfactual, alternative, history.

Moreover, while military history lends itself naturally to counterfactual analysis, other areas of history such as social or economic history where change is typically more gradual appear less suitable. After all: how is one to assess such complex counterfactuals as the fate of slavery in the US South in the absence of the Civil War?