What If? Counterfactualism and the Problem of History, by Jeremy Black; Social Affairs Unit, 2008, £10. I shall be telling this with a sigh Somewhere ages and ages hence: Two roads diverged in a wood, and I— I took the one less travelled by, And that has made all the difference. —Robert Frost, “The Road Not Taken” (1916) This short book, from the fertile pen of Jeremy Black, Professor of History at the University of Exeter, is about historical counterfactuals, in other words about the philosophy of history. A counterfactual is a proposition running counter to, or substantively “replacing”, in…