The duty of civility refers to the set of moral requirements that are associated with Rawls’s idea of public reason and its corresponding view of liberal-democratic political legitimacy. Indeed this duty is said to be one of the central “innovations” of Rawls’s theory of public reason (PL 253). It applies to both government oficials and ordinary citizens in the public political forum when they are resolving constitutional essentials andmatters of basic justice. The duty of civility instructs them to “be able to explain to one another on those fundamental questions how the principles and policies they advocate and vote for can be supported by the political values of public reason” (PL 217).

A principal obligation of the duty of civility, then, involves the practice of public justiication. Citizens and oficials should identify and sometimes publicly communicate suitable justifying reasons for their exercise of coercive political power, at least with respect to constitutional essentials andmatters of basic justice. Public justiication is “not simply valid reasoning, but argument addressed to others” (PL 465). It proceeds on the basis of public reasoning, that is, by way of ascertainable evidence and reasons and arguments drawn from a reasonable political conception of justice, consistent with the liberal principle of legitimacy based on the criterion of reciprocity. According to this criterion, the exercise of political power is legitimate only when “we sincerely believe that the reasons we would offer for our political activities – were we to state them as government oficials – are suficient, and we also reasonably think that other citizens might reasonably accept those reasons” (PL 447).