“The good” is an essential aspect of justice as fairness, but it has not yet been detailed and its application to the theory has not been established. The considerations of liberty and wealth do not alone lead to a complete conception of justice. Other primary goods must be considered. Parties to the original agreement’s conceptions of the good have a structure for them to rationally choose principles: “[I]n justice as fairness the concept of right is prior to that of the good,” and therefore two theories of the good must be established to apply to justice as fairness (347).

The thin theory of the good argues that something is good only if it is consistent with existing principles of right. The purpose of the thin theory “is to secure the premises about primary goods required to arrive at the principles of justice” (348). Once the thin theory of the good is worked out, a full theory of the good must be constructed to explain the social values and the stability of a conception of justice. The thin theory establishes that justice is in fact a good, and the full theory fleshes the details of justice as a good.