Naturalistic metaethics, external reasons, and the nature of moral argument

Desire-based accounts of practical argument about incompatible ends seem limited either to advice about means or to coercive threats. This paper argues that this can be avoided if the parties to the dispute desire its resolution by means other than force more than they desire the satisfaction of any particular ends. In effect, this means they must argue as if in a position of equal power. This leads to an explanation of the apparent objectivity of moral claims and of why moral reasons appear to be categorical and external. It also explains how notions such as reciprocal altruism and TIT-FOR-TAT can play a role in an evolutionary account of morality. The paper concludes with an argument to the effect that a desire-based metaethic must accept the is-ought gap and explains why there may appear to be no is-ought gap from within a given normative perspective.