Abstract: Prescriptive political and moral theories contain ideas about what human beings are like and about what, correspondingly, is good for them. Conceptions of human “nature” and corresponding human good enter into normative argument by way of support and justification. Of course, it is logically open for the ratiocinative traffic to run the other way. Strongly held convictions about the rightness or wrongness, goodness or badness, of certain social institutions or practices may help condition and shape one's responses to one or another set of propositions about what people are like and what, in consequence, they have reason to value.