The idea of reciprocity has always been central to Rawls’s thinking about justice. In A Theory of Justice he writes that reciprocity is “implicit in the notion of a well-ordered society” (TJ 13). But in his later work it plays an explicitly foundational role. Indeed, that work is based on the “fundamental idea … of society as a fair system of cooperation over time, from one generation to the next” (PL 14), and reciprocity is integral to that idea because “Fair terms of cooperation specify an idea of reciprocity: all who are engaged in cooperation and who do their part as the rules and procedure require, are to benefit in an appropriate way as assessed by a suitable benchmark of comparison” (PL 16). Reciprocity differs from pure altruism, in which one is motivated simply “by the general good,” and “mutual advantage,” under which everyone’s interests are advanced relative to a merely existing situation or baseline. In a relationship of reciprocity, by contrast to mutual advantage, “everyone benefits judged with respect to an appropriate benchmark of equality” (PL 17).