Couched in terms expressive of requirements or standards. A normative epistemology determines how you ought to conduct your cognitive life; a descriptive one only describes how people in fact do so. However, the distinction is not clear-cut in practice: according to the principle of charity the only way of interpreting what people do in fact think, is by assuming that by and large they think what they ought to think. The philosophy of social sciences is fraught with problems of distinguishing between fact and value. The central problem of normativity is identifying the source of the authority of moral, rational, cognitive or legal norms. See also Davidson, fact/value distinction, Weber.