Perhaps the most common philosophical view about the nature of morality is non-naturalistic moral realism. According to this view, moral properties or facts or truths exist as features of the objective, mind-independent universe – and they are, moreover, intrinsically normative and irreducible to naturalistic properties. The view seems to be at a special advantage in accounting for the objectivity and normativity of morality. There are, however, serious objections to it. I offer a new, strengthened epistemological objection to non-naturalistic moral realism by arguing that we could never rationally decide to accept our ordinary first-order moral beliefs (e.g. the belief that killing people for fun is wrong) if we were to understand them as beliefs about non-naturalistic realist normative truths. Thus, we could not maintain them in reflective equilibrium. This unacceptable skeptical outcome motivates my abandonment of non-naturalistic moral realism.

I develop an alternative metaethical theory by first examining other kinds of norms about which metaphysical and epistemological skepticism is rarely expressed. I focus on an ordinary game with a set of conventionally determined rules and argue that it can only be understood as a normative practice – that is, as constituted by a set of norms that provide reasons and requirements to the players in virtue of their commitment to it. Further investigation yields a response-dependence biconditional which indicates how the relevant reasons and requirements are determined by people's judgments. I argue that this response-dependence biconditional both provides for a constructivist, anti-realist account of the relevant reasons and requirements, and also provides for an explanation of how we can rationally accept our most reflective beliefs about them.

My theory is extended to account for diverse kinds of reasons and requirements by showing why and how we construct different kinds of normative practices. I sketch the nature of, and some of the differences between, the normative practices that I believe account for the instrumental, epistemic, and aesthetic reasons and requirements that we are subject to. Finally, I offer a response-dependence account of morality as a cooperative normative practice by combining T.M. Scanlon's contractualist formula with a sentimentalist account of reasonable objections to candidate principles.