Natural duties and obligations are “an essential part of a conception of right: they define our institutional ties and how we become bound to one another” (293). A conception of justice requires them: “[T]he most important natural duty is that to support and to further just institutions” (293).

The natural duty of justice is to support and further the arrangements and institutions that satisfy the two principles of justice. This being a duty, not an obligation, eliminates the assurance problem as a concern. Other important natural duties are the duty of mutual respect and the duty of mutual aid. The duty of mutual respect:

is the duty to show a person the respect which is due to [them] as a moral being, that is, as a being with a sense of justice and a conception of the good. […] Everyone benefits from living in a society where the duty of mutual respect is honored” (297).

The duty of mutual aid is based on the reality that if persons do not make public their own duty to aid others when in need, they cannot expect aid from others when they are in need: “The public knowledge that we are living in a society in which we can depend upon others to come to our assistance in difficult circumstances is itself of great value” (298).