"Liberalism has always had two faces," the English philosopher John Gray asserts in his remarkable new book on the liberal political tradition. The earliest theories of liberalism were formulated in the 17th and 18th centuries by European thinkers like Thomas Hobbes, who sought to devise a social order in which members of rival Christian denominations could live in peace. Since the Enlightenment, however, liberalism has been warped by utopian schemes purporting to promote a social order free of conflict. These schemes are incoherent in theory as well as impossible to apply to the real world. At the beginning of the 21st century, Gray argues, the liberal tradition can be rescued only if its original rationale is revived and adapted to a world in need of a formula for peaceful coexistence among rival communities defined more by culture than by religion. That formula for peaceful coexistence Gray calls "modus vivendi."

This, in essence, is the argument of this brief, elegant and powerful book, which seeks to effect a revolution in the way we think about the nature of liberalism in concept and practice. Gray, a professor of European thought at the London School of Economics, is no stranger to controversy. A prolific author who has published studies of Isaiah Berlin, John Stuart Mill and Voltaire, he has intervened frequently in public debates, relishing the kind of polemical journalism that his more cloistered colleagues disdain. A libertarian defender of Margaret Thatcher in the 1980s, he has become a supporter of the transatlantic "third way" centrism associated with President Clinton, British Prime Minister Tony Blair and German Chancellor Gerhard Schroeder.

But despite his accomplishments as a historian and publicist, Gray is first and foremost a philosopher. In "Two Faces of Liberalism," as in a number of books and articles over the last two decades, including "Enlightenment's Wake" and "False Dawn," Gray has sought to tease out the implications, for liberal and democratic political theory and practice, of "value pluralism," the perception that virtues and ideals, which all agree are good in themselves, may conflict with one another. The idea of the plurality of incompatible values was emphasized by Berlin, who, along with the late Michael Oakeshott, another 20th century British philosopher, has had a profound influence on Gray. "Unlike most liberal thinkers," Gray writes, "Berlin understood that liberty is not one thing but many, that its various components do not all mesh together but often clash, that when they do conflict there is inevitably loss and sometimes no solution that all reasonable people are bound to accept."

Berlin, like Mill, was influenced by the German romantic theorists of the "counter-enlightenment," who defended the value of unique cultures against the rationalizing uniformity championed by the French philosophes. According to Gray, neither Mill nor Berlin was able to resolve the tension between enlightenment ideals of universalism and individualism and romantic cultural particularism. "We need not see the failure of Mill's enterprise, or of Berlin's, as the failure of liberalism," Gray writes. By adopting the idea of liberalism as a modus vivendi among multiple value systems, "we will take a further step in an intellectual pilgrimage begun by John Stuart Mill and continued in our own time by Isaiah Berlin, and resolve an ambivalence that has beset liberalism throughout its history."

Gray spends much of "Two Faces of Liberalism" criticizing thinkers who evade the tension between universalism and particularism in liberal thought by coming down squarely for one or the other side. Philosophers like John Rawls and Robert Nozick, who purport to deduce the ideal regime from this or that set of a priori premises, are trying to accomplish the impossible (something which, as Oakeshott was fond of observing, is an inherently corrupting enterprise). "If we think of liberalism as a prescription for an ideal regime," Gray argues, "it is undone by conflicts of value that liberal principles are powerless to resolve." The reason is that "the warrior virtues that are celebrated in the Iliad and the self-examination practiced by Socratic inquirers; the virtues of duty and detachment exemplified in the Bhagavad-Gita and the universal compassion preached by the Buddha; the ideal of self-creation which is articulated in Proust's 'Remembrance of Things Past' and the holy simplicity embodied in Alyosha in Dostoevsky's 'Brothers Karamazov'--these ideals are rivals." Philosophers who try to spell out the details of the ideal society usually end up creating idealized versions of their own societies: Aristotle's polis, Hegel's Prussia, the Rawlsian and Nozickian versions of the United States of America.

Gray is equally critical of communitarians, whose answer to moral and political dilemmas is immersion in a single all-encompassing tradition. Outside of subcultures like those of the Amish and Hasidic Jews, communitarianism is of little relevance in complex modern societies: "The access to different ways of life that comes with mass immigration and new technologies has made the capacity to harbor dissonant values and views of the world an essential part of many people's lives. A world in which people are defined by membership of a single community is not only far removed from that in which we live. It is not seriously imaginable by us." Taken to an extreme, the belief by proponents of extreme cultural determinism that "there is no such thing as human nature is as much an illusion as the Enlightenment idea of universal harmony. Like other animals, humans have a common nature that is fairly constant in its needs."

To prevent a modus vivendi among various cultures from degenerating into amoral relativism, Gray proposes replacing the fulfillment of universal human rights with the protection of universal human needs as a government's primary responsibility. "The requirements of legitimacy that all contemporary regimes should meet are not the free-standing rights of recent liberal orthodoxy," he explains. "They are enforceable conventions, framed to give protection against injuries to human interests that make any kind of worthwhile life impossible." Because of this, Gray claims, "Liberals and pluralists walk side by side in resisting totalitarian and fundamentalist regimes." Gray's needs-based criterion of political legitimacy would exclude societies like National Socialist Germany, South Africa and Mao Tse-tung's China, but not, he says, authoritarian Singapore or Castro's Cuba. In the last decade, many critics have objected to Gray's frequently repeated assertion that some nondemocratic and nonliberal regimes may adequately meet the needs of their people. The alternative, though, is to dismiss almost all long-enduring governments in recorded history, and many of those in the United Nations, as inherently illegitimate.

Perhaps the most debatable element of Gray's argument is his assessment of the challenge that minority cultures pose to majority cultures in contemporary societies. In nation-states like the United States, minorities that diverge greatly from the norm tend to be small and encapsulated, like the Amish and Hasidim, and immigrants tend to assimilate into the mainstream in a few generations. Several of the multinational countries to which Gray alludes--Indonesia and Israel, for example--are more likely to solve their ethnic problems by more or less brutal partition rather than by the devices of territorial and cultural pluralism that Gray cautiously favors. If this is the case, then the idea of modus vivendi may find its greatest relevance as a principle of international order in a world permanently divided among societies with radically different traditions more than as a principle of domestic politics. In his "New Year Letter" (1940), W. H. Auden wrote:

We hoped; we waited for the day
The State would wither clean away,
Expecting the Millennium
That theory promised us would come, It didn't. Specialists must try
To detail all the reasons why...

Gray's minimalist liberalism goes a long way toward answering the need for a low but solid public philosophy in an era in which millennial political creeds have been discredited. If Gray is right, liberalism can be rescued from liberal theorists but only if it returns, chastened, to its modest origins. "The philosophies of John Locke and Immanuel Kant exemplify the liberal project of a universal regime, while those of Thomas Hobbes and David Hume express the liberalism of peaceful coexistence. In more recent times, John Rawls and F.A. Hayek have defended the first liberal philosophy, while Isaiah Berlin and Michael Oakeshott are exemplars of the second." With this masterly summa, John Gray has earned a place for himself in the tradition of Hobbes, Hume, Berlin and Oakeshott.