Foucault appears to challenge traditional views of truth, reason, and knowledge in the doctrine of power/knowledge developed in his post?1970 writings. This doctrine applies to all the sciences (and to non?scientific and non?discursive practices that are not discussed here). Foucault's notions of discourse (1) and power (3) are sufficiently discussed to set out his explanatory theory of the cause of our discourses and their change. In (4) three theses concerning the power/knowledge link are distinguished, of which the more important is (...) called the ?Primacy Thesis?, namely the causal priority of power over knowledge. Various formulations of this thesis are investigated, some of which are contrasted with Francis Bacon's more plausible account of the link between power and knowledge. In (5), six criticisms of the thesis are discussed. Foucault's notion of truth is explored on the way, more particularly in (6). The outcome of the discussion is that Foucault's doctrine of power/knowledge, apart from some insights for an empirically based sociological investigation into the causes of some of our scientific beliefs, is generally false; for philosophical theories of truth and knowledge it has nothing to say. In fact if Foucault is to be a critic of the beliefs which circulate as a result of power, he needs the traditional account of truth and knowledge. (shrink)