Although any theory of distributive justice always requires some sort of interpersonal comparison, the possibility of interpersonal comparison remains one of the fundamental problems in theories of distributive justice, including Rawls’s difference principle. The problem of interpersonal comparison concerns the question of whether we can compare the state of one person with that of another (Hammond 1991).

In economics, there is a deep and abiding skepticism about interpersonal comparisons. Many economists base their theories on individual preferences. But it is widely thought that there is no scientiic basis to compare a person’s mental states with another’s, and that interpersonal comparisons cannot be done without including some normative judgments. Skeptics argue that, for economics to be a branch of science, it must eliminate any normative elements and thus avoid interpersonal comparisons. Economists instead appeal to a Pareto principle (e.g. the weak Pareto principle holds that if every person in society strictly prefers a state of affairs x to y, x is socially preferred to y) to construct a collective decision-making rule. However, Pareto principles are silent about distributional justice.

Rawls thinks that there is no need for interpersonal comparisons of overall well-being. His theory of justice only requires some basis for interpersonal comparison of what is relevant from the point of view of justice. This is why Rawls appeals to the notion of primary “social” goods. Rawls claims that the notion of primary social goods offers “the most feasible way to establish a publicly recognized objective measure, that is, a common measure that reasonable persons can accept” (TJ 81). According to Rawls, if primary social goods are used as the informational basis of distributive judgments, the problem of interpersonal comparison does not arise.