Controversy over the adequacy of the regularity or covering law theory of explanation when applied to historical actions continues to rage. A detailed analysis is here made of Professor A. Donagan's recent attack on this theory, as representative of many others. His alternative model of deductive non-law explanation, based on Popper's notion of the "logic of the situation," is then shown to be invalid and generally defective. Finally, four sources of the difficulty are elicited which, when resolved, provide support for (...) the regularity theory in its probabilistic version. We suggest that this theory, despite recent criticism, can be fruitfully extended to historical explanation by uncovering and codifying a major difference between history and science, the rational actions of historical agents, without distorting it. (shrink)