In a theory of justice (§64 and elsewhere), “deliberative rationality” is Rawls’s name for our capacity of reflective choice – a capacity that transcends the various principles of rational choice of which it makes use. It operates on that range of choices still left over once the explicit principles of rational choice have been exhausted. Rawls gives a simple example of planning a holiday, one on which we want to study a certain kind of art. This aim rules out various possible destinations, but leaves us with Paris and Rome as equally good prospects. We also care about seeing Christendom’s most famous church and its most famous museum; but since Paris and Rome each score one for two on these, this will not advance our decision. “[S]ooner or later,” Rawls comments, “we will reach incomparable aims between which we must choose with deliberative rationality” (TJ 483).

In addition to being of interest in its own right, this conception of deliberative rationality plays two important roles in Rawls’s theory, each motivated by the thought that the idea of goodness cannot be adequately captured by the principles of rationality that people have so far succeeded in articulating. First, it is an important working part of Rawls’s definition of the good for persons, thus indirectly contributing to Rawls’s account of the good of justice, and hence to his argument for the potential congruence between justice and the good in the well-ordered society of justice as fairness. Second, it does important work in Rawls’s criticism of the kind of unity of self available to teleological (good-based) views, paving the way for his account of the superior unity of self offered by deontological theories.