This is not, in the ordinary run of things, the sort of book that one would find reviewed in a magazine aimed at "the general reader". The papers it contains are almost all of a technical kind; the writing is harder than it might be. Yet some theorists are so important, their influence so enormous, that the appearance of a new book, no matter how recondite, becomes a public event. One such is John Rawls.
Since the publication of the ground-breaking A Theory of Justice, in 1971, Rawls has been recognised as the most important English-speaking political philosopher of his generation. In fact, he is now often said to be the most important political philosopher of the century in any language. These rankings are silly, if irresistible. The point is that Rawls, through a mixture of bold thought experiment, conceptual rigour and historical imagination, more or less invented analytic political thought. It is true that his brand of left-wing liberalism has had very little direct influence beyond the academy, but undoubtedly it has indirectly exerted subtle effects outside academia. Anyway, he would not be the first important philosopher to be neglected by the common herd.
Although Rawls is now nearly 80, Collected Papers represents only his third book. The first, A Theory of Justice, the product of more than 20 years' work, was important for at least three reasons. First because of the conception of political philosophy it embodied. The task of the political philosopher, as Rawls presented it, was to find principles that underlay our settled convictions of justice and then use these principles in turn to settle more difficult problems. So one might start with principles such as that slavery is wrong, women are equal to men and the old and infirm should not be allowed to starve, and then elaborate more abstract principles that might underpin these. These abstract principles will in turn guide us in tackling more contentious political dilemmas, while at the same time, these new dilemmas can always force us to rethink fundamental political principles. This adjustment of first principles and practical convictions should go on, Rawls held, until one arrives at a "reflective equilibrium". Political deliberation could, it turned out, be more or less rational - it was not that far from other forms of deliberation about, say, the empirical world.
Second, A Theory of Justice gave human rights a philosophical foundation. Where the dominant political philosophical tradition in the English-speaking world, utilitarianism, gave rights a derivative status - they were only valuable in so far as they advanced the general good - Rawls argued that the first duty of the state was to protect individual rights against the claims of the general good. Utilitarian theories have been on the defensive ever since. Third, Rawls offered an innovative and contentious principle of distribution - "the Difference Principle" - according to which inequalities in a society are only justified to the extent that they benefit the worst-off.
A Theory of Justice was followed, in 1993, by Political Liberalism, which marked a new direction in Rawls's thought. The first book was criticised from many angles, but one of the most common complaints against it was that, in one way or another, it drew on a series of only half-articulated and highly debatable liberal prejudices. Rawls himself acknowledged the truth of these complaints in so far as he came to admit that A Theory of Justice had rested on a single liberal conception of the good life (famously championed by Kant and Mill), according to which each of us has a duty to search out our own good from among the available alternatives. This is not a vision that would be acceptable to, say, a Catholic; Catholicism teaches that a life that faithfully accepts church tradition is superior to one spent ceaselessly exploring moral alternatives - it rates fidelity and submission over autonomy or experimentation.
So Rawls now altered his position in two significant ways. First, he recast his conception of justice as "political not metaphysical". That is, he now suggested that his principles of justice did not have to rest on questionable liberal beliefs about the nature of the person or the good life; they are ones that all members of our multicultural societies share. Public justifications can and must stand above philosophical, religious and cultural issues on which we are bound to disagree.
Second, he also conceded that the principles he had championed in A Theory of Justice might not be universally valid: they gave expression to our western political ideals and traditions.This was a very Rawlsian strategy; Rawls conceded as much as possible to his opponents in order to get agreement on what he believes is the really important issue, the principle of justice. Unfortunately, while this somewhat sceptical turn won Rawls some friends among his former critics, he lost as many purer-minded liberals along the way. The new position has its own tensions. It is one thing to suggest that non-liberals and liberals might all be persuaded to agree on principles of tolerance and equal opportunity. But it is quite another to expect people of very different world-views ever to agree on something as radical as the Difference Principle.
This fascinating collection of papers gathers together some 25 articles written between 1951 and 1997, which sketch out and defend ideas found in A Theory of Justice and Political Liberalism. Some offer helpful elucidations of ideas embedded in the larger books. In the "Preface for the French edition of A Theory of Justice" Rawls writes more forthrightly than hitherto about the practical implications of his ideas, arguing that his principles of justice are not realisable in a welfare state, only in an egalitarian "property-owning democracy", or a "liberal socialist regime". This should give the lie once and for all to those left-wing critics who claim that Rawls is merely an apologist for liberal capitalism. In "Fifty Years After Hiroshima", a rare venture into a concrete political debate, Rawls criticises the decision to drop atomic bombs on Japanese civilians as a violation of the laws of war, as properly understood. However, it is not just the new insights and arguments that make these papers worth reading; the doggedness, imaginativeness and seriousness they evince is utterly admirable. There is something especially noble in the way Rawls is always working to take new criticism on board. Just one example: A Theory of Justice envisioned the family as a natural non-political unit. As a result of feminist criticisms, however, Rawls has come to acknowledge that the family itself can both harbour injustices and form unjust desires in its members. For this reason it, too, he claims, is "a matter for political justice" - the state, for instance, should act to advance the rights of wives and the interests of children. Rawls is always willing to learn and to change.
Ben Rogers is the author of "A J Ayer" (Chatto & Windus, £20)