Barry Barnes and David Bloor of the Strong Programme of the sociology of knowledge advance a naturalized epistemology that reduces all accounts of normativity to social causes. I endorse their program of naturalizing one kind of normativity, but I argue that there is another kind they cannot naturalize. Within the context of sociological explanations of rationality, there are norms of rationality instantiated by scientists that Barnes and Bloor study, and Barnes and Bloor's own normative ascriptions of scientists as rational beings. (...) I argue that Barnes and Bloor successfully justify their naturalization of the norms of rationality of the scientists they describe by a methodological caution and arguments from under-determination and finitism. But they inevitably fail to naturalize their own normative ascriptions of those scientists as rational. (shrink)