An examination of footnotes, quotations, and name-lists shows that historians try to follow the reality rule - to tell about the past the most likely story that can be sustained by the relevant existing evidence. But this is modified by the maximum impact rule - stories must have evocative force, and the reader should actively confront the past. The maximum impact rule may require the historian to sacrifice some completeness and exactness for evocative impact; and there is no parallel to this sacrifice in scientific explanations. History, as it is practiced, is a rule-bound discipline, with rules and a rhetoric different from those of scientific explanation. There is no need for historians to structure their explanations according to the pattern of the sciences.