The aim of a theory of justice appears to be to find an explanation of our intuitive judgments in this area, an explanation which is capable of yielding, at any rate eventually, answers to particular questions of social policy. The difficulty of constructing such a theory is due partly to the many elements in the concept of justice. To assert that there is more than one concept of justice would be to take the easy way out; to say that there is only one simple concept, as Robert Nozick appears to do (Anarchy, State, and Utopia, Princeton, 1974) is to narrow to an unwarranted extent the application of the concept.

Any adequate concept of justice must include amongst its ingredients fairness, entitlement or right, desert, need, reciprocity and the relative paramountcy of the concept. Nozick's historical-entitlement theory explains both the connection of justice with entitlement and the relative paramountcy of the concept. But it does not show, as it should, the connection of entitlement with the other elements in the concept of justice.