The prescriptive force of methodological rules rests, I argue, on the acceptance of scientific theories; that of the most general methodological rules rests on theories in the philosophy of science, which differ from theories in the several sciences only in generality and abstraction. I illustrate these claims by reference to methodological disputes in social science and among philosophers of science. My conclusions substantiate those of Laudan except that I argue for the existence of transtheoretical goals common to all scientists and concrete enough actually to have bearing on methodology. And I argue that Laudan is committed to such goals himself, willy nilly.