The search for a nomological account of what determines the content of concepts as they are represented in cognitive systems, is an important part of the general project of explaining intentional phenomena in naturalistic terms. I examine Fodor's (1990a) "Theory of Content" and criticize his strategy of combining constraints in nomological terms with contraints in terms of actual causal relations. The paper focuses on the problem of the indeterminacy of the content of natural kind concepts. A concept like water can pick out either a phenomenological property or a scientific one. Moreover, even on the assumption that the latter is shown to be most adequate, a given sample will still come out as falling into different natural kinds, according to the taxomomy of each particular science of which it constitutes an object. Both chemistry and physics contain concepts which are scientific counterparts of the common sense concept water, yet their extensions differ. As a criterion for determining the most relevant science for a given concept, I suggest to ask which science is most specific for the typical interactions of the subject possessing the concept, with her environment. The use of this criterion also permits one to show that a nomological theory is not necessarily verificationist, contrary to what has been claimed by Fodor and Boghossian (1991).