Does empirical moral psychology rest on a mistake?

Many philosophers assume that philosophical theories about the psychological nature of moral judgment can be confirmed or disconfirmed by the kind of evidence gathered by natural and social scientists (especially experimental psychologists and neuroscientists). I argue that this assumption is mistaken. For the most part, empirical evidence can do no work in these philosophical debates, as the metaphorical heavy-lifting is done by the pre-experimental assumptions that make it possible to apply empirical data to these philosophical debates. For the purpose of this paper, I emphasize two putatively empirically-supported theories about the psychological nature of moral judgment. The first is the Sentimental Rules Account, which is defended by Shaun Nichols. The second is defended by Jesse Prinz, and is a form of sentimentalist moral relativism. I show that both of the arguments in favour of these theories rely on assumptions which would be rejected by their philosophical opponents. Further, these assumptions carry substantive moral commitments and thus cannot be confirmed by further empirical investigation. Because of this shared methodological assumption, I argue that a certain form of empirical moral psychology rests on a mistake