"The ultimate merit of Rawls’s work did not lie only in his own theory, but in the extraordinarily broad discussion that it generated. Rawls’s work provided a framework for a flurry of counter-theories, such as G.A. Cohen’s in Rescuing Justice and Equality, which challenged Rawls from the left and advocated a stricter egalitarianism; and Robert Nozick’s sophisticated libertarian response in Anarchy, State, and Utopia; and Michael Walzer’s development, in Spheres of Justice, of a communitarian approach to the problem."