In this paper I present a relation between two principles on individuals that John Rawls presented in his two major works. First one is natural duty of justice in A Theory of Justice and second one is moral duty of civility in Political Liberalism. I start with the claim that natural duty of justice is the best answer to the problem of legitimacy of liberal institutions posed by A. John Simmons. But, in the circumstances of reasonable pluralism it is not clear how can such a vague duty guide us in political reasoning. That is why I claim that moral duty of civility, which demands that we respect boundaries of public reason, is the way how we fulfill our natural duty of justice in circumstances of reasonable pluralism. This implies that moral duty of civility has its moral grounding in natural duty of justice. Then I try to present how this view can answer to some objections raised against the idea of public reason and also how it can refers to some problems of distributive justice.
