A few friends and colleagues have asked me why I think Rawls and not, say, Nozick, was the best political philosopher of the 20th Century. What kind of libertarian am I to think that? Well, I certainly think Nozick gets the conclusions right. But I truly think A Theory of Justice is an incredibly rich and profound book that lays out an extremely compelling method for evaluating the moral desirability of basic social and political institutions. Nozick's Anarchy, State, and Utopia is in my opinion one of the most, if not the most, compelling, creative, and pyrotechnically brilliant pieces of extended reasoning in all of 20th Century philosophy. But it famously begins with an unsupported assumption of John Locke-style individual rights. If you don't accept the assumption, the argument just doesn't get going.
Rawls, I think, offers a compelling way of justifying something like rights as side-constraints. Now, I don't think many of Rawls' conclusions follow from his intermediate premises. For instance, Rawls' does not take sufficiently seriously his own claim for the moral priority of his First Principle of Justice, "each person is to have an equal right to the most extensive basic liberty compatible with a similar liberty for others," over his Second Principle, that inequality in the "distribution" of "primary goods" is justified only if it benefits the least well-off class of citizens. Additionally, even if one accepts Rawls' second principle (I think it is too strong), his conclusions about how it justifies certain institutions of the modern welfare state don't follow, given what is known, empirically and theoretically, about economics and political economy. Nevertheless, I think Rawls' theoretical framework is very close to the right one, and that is an enormous achievement. My own view is very close to that of Richard Epstein in his remembrance of Rawls in the National Review:
The great irony here is that the Rawlsian construct in the end supplies, I believe, the strong intellectual foundation for a political system with which he had only scant affinities: classical liberalism, with strong property rights and limited government. The irony is even greater when Rawls's work is conjoined with Nozick's, for the latter recoiled from the formal procedures so championed by Rawls, and used ingenious, if intuitive, arguments to defend the primacy of individual autonomy and private property even though, with the benefit of hindsight, these are more strongly defended by an astute application of the veil-of-ignorance technology.
I think Epstein (and most everyone) over-emphasizes the importance of the "veil of ignorance" in Rawls' system, but I think he's close to the bullseye.
It's worth noting that Hayek himself endorsed the broad outlines of Rawls' basic theoretical framework. From Law, Legislation, and Liberty, Volume 2: The Mirage of Social Justice, p. 100, Hayek writes:
... there unquestionably ... exists a genuine problem of justice in connection with the deliberate design of political institutions, the problem to which Professor John Rawls has recently devoted an important book. [Vol 2 of LL&L was published in 1976.] The fact that I regret and regard as confusing is merely that in this connection he employs the term ’social justice’. But I have no basic quarrel with an author who, before he proceeds to that problem, acknowledges that the task of selecting specific systems or distributions of desired things as just must be "abandoned as mistaken in principle, and it is, in any case, not capable of a definite answer. Rather the principles of justice define the crucial constraints which institutions and joint activities must satisfy if persons engaging in them are to have no complaints about them. If these constraints are satisfied, the resulting distribution, whatever it is, may be accepted as just (or at least not unjust)." This is more or less what I have been trying to argue in this chapter.
Hayek's claim that the idea of "social justice" is a kind of category error is right on. The pattern of holdings that arise from voluntary cooperative exchange according to just rules is not itself a subject of moral evaluation, and the attempt to "correct" the pattern according to some moral principle requires rules of social interaction that are unjust--a point Nozick makes with great force and lucidity in his section on "How Liberty Upsets Patterns" in Anarchy, State, and Utopia. Rawls' waffles on this point, distinguishing between "distribution," which he takes to be the emergent outcome of interaction according to the rules of the "basic structure" of a society's institutions, and "allocation," the coercive redistribution of holdings. Rawls claims to be concerned with distribution in this sense, but it's pretty clear he's often attempting to justify broad "allocative" powers for the state.
Nevetheless, the depth and scope of what Rawls gets right is incredible. Join that to the fact that his later major work, Political Liberalism--a profound and innovative meditation on the meaning of liberal neutrality in pluralistic societies--has a fairly straightforward libertarian reading (despite his protestations to the contrary), and I think Rawls takes the laurels. Of course, these judgments are complex and depend on how heavily one weighs various valuable aspects of philosophical works, so others might reasonably come to different conclusions. But I think my judgment here is on pretty solid ground.
Special bonus! Who are the greatest political philosophers of the past few centuries, according to my idiosyncratic judgment? 19th C.: Herbert Spencer (maybe the most unjustly maligned thinker ever) by a hair over J.S. Mill and Henry Sidgwick. 18th C.: David Hume over Adam Smith by a nose. 17th C.: Thomas Hobbes by a nose over John Locke, for reasons similar to Rawls vs. Nozick. I also think the Rolling Stones were better than the Beatles.