Although the methodological approach of using history of science in philosophical theorizing in science has a long tradition, a central issue has hitherto not been addressed in a satisfying fashion: how can facts about science ground philosophical norms about science? This chapter criticized two solutions proposed by Laudan. It then goes on to argue that in one viable approach within the history of science, namely the “Kuhnian mode of HPS”, historical facts may motivate philosophical norms about science without having to serve as justifiers for them. The chapter also advocates Lakatos’ idea of maximizing the number of historical facts which can be explained in a rational way (without distorting them). Finally, the chapter rejects the view that philosophical norms must always be categorical and suggests that ceteris paribus norms may be more appropriate in many contexts. The second part of the chapter argues that another fruitful role for the history and philosophy of science is concept clarification: although descriptive, it is also normative as explicating conditions which are normally left implicit can help us arbitrate between correct and incorrect uses of the concept.