 The final contenders in the political obligation debates are natural duty accounts. In this context, natural duties are understood to be ones people have simply in virtue of their status as moral agents; they need do nothing to acquire them, nor does their bearing such duties depend on their occupying some role in a socially salient relationship. Natural duties are also universal in scope; they are owed to all members of a class defined in terms of possession of some feature, such as sentience or rationality. John Rawls first broached such an argument for political obligation when he asserted in A Theory of Justice that everyone is subject to a natural duty of justice that “requires us to support and to comply with just institutions that exist and apply to us” (1999, p. 99). More recently, political philosophers and theorists including Jeremy Waldron (1999), Thomas Christiano (2008), Christopher Heath Wellman (2005), Anna Stilz (2009) and, arguably, David Estlund (2008; see section 4.1 above) have refined and expanded upon Rawls’s somewhat vague contention, some of them in ways reminiscent of or even explicitly modeled on Kant’s defense of political obligation (see section 1.5 above).