Constitutivism is the view that we can justify fundamental normative claims by showing that agents become committed to these claims merely in virtue of acting.1 Constitutivists aspire to show that action has structural features – constitutive aims, principles, or standards – that are present in each instance of action and that generate substantive normative conclusions. In showing that the authority of fundamental normative claims is sourced in our own actions, constitutivists hope to avoid familiar objections to justificatory projects in ethics.