The arguments for the principles of the natural duty

In an earlier chapter (§§18–19) I described briefly the principles of natural duty and obligation that apply to individuals. We must now consider why these principles would be chosen in the original position. They are an essential part of a conception of right: they define our institutional ties and how we become bound to one another. The conception of justice as fairness is incomplete until these principles have been accounted for. From the standpoint of the theory of justice, the most important natural duty is that to support and to further just institutions.

This duty has two parts: first, we are to comply with and to do our share in just institutions when they exist and apply to us; and second, we are to assist in the establishment of just arrangements when they do not exist, at least when this can be done with little cost to ourselves. It follows that if the basic
structure of society is just, or as just as it is reasonable to expect in the circumstances, everyone has a natural duty to do what is required of him. Each is bound irrespective of his voluntary acts, performative or otherwise. Now our question is why this principle rather than some other would be adopted. As in the case of institutions, there is no way, let us assume, for the parties to examine all the possible principles that might be proposed.

The many possibilities are not clearly defined and among them there may be no best choice. To avoid these difficulties I suppose, as before, that the choice is to be made from a short list of traditional and
familiar principles. To expedite matters, I shall mention here only the utilitarian alternative for purposes of clarification and contrast, and very much abbreviate the argument. Now the choice of principles for individuals is greatly simplified by the fact that the principles for institutions have already been adopted. The
feasible alternatives are straightway narrowed down to those that constitute a coherent conception of duty and obligation when taken together with the two principles of justice.1 This restriction is bound to be particularly important in connection with those principles definitive of our institutional ties. Thus let us suppose that the persons in the original position, having agreed to the two principles of justice, entertain the choice of the principle of utility (either variant) as the standard for the acts of individuals. Even if there is no contradiction in this supposition, the adoption of the utilitarian principle would lead to an incoherent conception of right.

The criteria for institutions and individuals do not fit together properly. This is particularly clear in situations in which a person holds a social position regulated by the principles of justice. For example, consider the case of a citizen deciding how to vote between political parties, or the
case of a legislator wondering whether to favor a certain statute. The assumption is that these individuals are members of a well-ordered society that has adopted the two principles of justice for institutions and the principle of utility for individuals. How are they to act? As a rational citizen or legislator, a person should, it seems, support that party or favor that statute which best conforms to the two principles of justice. This
means that he should vote accordingly, urge others to do likewise, and son. The existence of institutions involves certain patterns of individual conduct in accordance with publicly recognized rules

The principles for  institutions have, then, consequences for the acts of persons holding positions in these arrangements. But these persons must also regard their actions as governed by the principle of utility. In this case the rational citizen or legislator should support the party or statute whose victory or enactment is most likely to maximize the net balance (or average) of satisfaction. The choice of the utility principle as the standard for individuals leads to contrary directives. To avoid this conflict it is necessary, at least when the individual holds an institutional position, to choose a principle that matches in some suitable way the two principles of justice. Only in noninstitutional situations is the utilitarian view compatible with the agreements already made. Although the principle of utility may have a place in certain duly circumscribed contexts, it is already excluded as a general account of duty and obligation. The simplest thing to do, then, is to use the two principles of justice as a part of the conception of right for individuals.