ABSTRACT
It is a commonplace of historiography that not only the kind of explanation we give of historical events and processes, but also what we define as significant and deserving of explanation in the first place, depends upon a set of prior assumptions that may be unstated or only barely articulated. In particular, the identification of a historical outcome as significant because unexpected, and there fore as raising a special problem for explanation, depends upon assumptions about what could reasonably have been expected, about what a typical course of events would have been. Such counterfactual assumptions are no mere idle fancy or speculation, but constitute one of the standard bases for the selection of historical problems. It is a task of historical theory, though by no means an uncontroversial one, to render the assumptions underlying such processes of selection explicit, so that they can be subjected to examination and, where possible, made more secure.
