Historians often appear skeptical of counterfactual arguments. E.H. Carr argued that “a historian should never deal in speculation about what did not happen” (Carr, 1961, 127). Michael Oakeshott described counterfactual reasoning as ‘a monstrous incursion of science into the world of history’ (quoted in Ferguson, 1999). More recently, Eric Foner is reported to have found “counterfactuals absurd. A historian’s job is not to speculate about alternative universes …It’s to figure out what happened and why” (cited in Parry, 2016, here).
Such skepticism is striking to the modern economic historian, who since Robert Fogel’s work on the impact of the railroad on American economic growth has been trained to think explicitly in terms of counterfactuals. Far from being the absurdity Foner suggests, counterfactuals represent the gold standard in economic history today. Why? Because they are the sine qua of causal analysis. As David Hume noted, a counterfactual is exactly what we invoke whenever we use the word “cause”: “an object, followed by another, . . . where, if the first object had not been, the second would had never existed” (Hume, 1748, Part II).
Hume’s reasoning can best be understood in the context of a controlled experiment. Suppose a group of randomly selected patients are treated with a new drug while another randomly selected group are assigned a placebo. If the treatment and control groups were ex ante indistinguishable, then the difference between the outcomes for these two groups is the causal effect of the drug. The outcome for the control group provides the relevant counterfactual which enables us to assess the effectiveness of the drug.
The modern revival of economic history is based largely on the skill with which economic historians have been able to use econometric tools to replicate this style of experimental design using observational data. Such techniques enable economic historians to assess such counterfactuals as how much did slavery contribute to Africa’s underdevelopment?, what was the impact of the Peruvian Mita? or the effects of the Dust bowl?
The rejection of the counterfactual approach by historians such as Foner seems to run deep and constitutes a major divide between historians and economic historians; it is therefore well worth exploring its source.