Rawls treats social cooperation as voluntary activity between citizens of a common polity that generates beneits for cooperators. Fair social cooperation is regulated by public rules and procedures that all can freely accept as appropriate. Rawls’s principles of justice apply to the basic institutional structures of society that deine the fair terms of social cooperation. An accurate representation of the fundamental idea of society as a fair system of cooperation is thus essential to understanding the overall character of Rawls’s theory. Rawls maintains that justice as fairness adopts an understanding of social cooperation that is animated by an idea of reciprocity or reciprocal advantage. He locates reciprocity between an idea of impartiality and an idea of mutual advantage. The contrast between these ideas lies in the different relation citizens engaged in cooperation can stand both to one another and to the beneits that cooperation generates.

Reciprocity assumes that citizens in a well-ordered society view each other as free and equal persons who are jointly committed to establishing fair terms of cooperation. Each citizen is concerned to advance her own good through cooperation but this concern is tempered by an acknowledgement of the reasonable claims of others. So each citizen need not extract the maximum benefit from a scheme of social cooperation that they can secure via rational bargaining in order for a scheme to be fair. Reciprocity requires both that all contribute to social cooperation and that social cooperation be beneicial to all. However, the benchmark for assessing whether cooperation beneits all is an equal division of social beneits.