In 1971, a previously obscure Harvard philosophy professor, John Rawls, published a book that ultimately brought him acclaim as "America's greatest political philosopher." In the book, "A Theory of Justice," Rawls set forth an account of justice in the form of two principles, ordaining respectively that people's "equal basic liberties"  such rights as freedom of speech, freedom of conscience, and the right to vote  should be maximized, and that inequalities in social and economic goods other than liberty are acceptable only if they promote the welfare of the "least advantaged" members of society. (He termed the latter the "difference principle.")

Three years after the appearance of "Theory," a departmental colleague of Rawls, Robert Nozick, published a libertarian response, "Anarchy, State, and Utopia," which argued that nothing more than a "minimal state" devoted to protecting people against crimes like assault, robbery, and fraud could be morally justified.

Nozick's book was far more concise than Rawls's "Theory," and "Anarchy, State, and Utopia" did not go unnoticed: It won the 1975 National Book Award and was later listed by the Times Literary Supplement as one of the 100 most influential books of the 20th century. "Anarchy" remains a staple of the syllabus in courses on political theory, where it is usually juxtaposed with selections from Rawls to suggest that Rawls's welfare-state liberalism and Nozick's libertarianism represent the full spectrum of possibilities for contemporary liberal democracies.

Nonetheless, Nozick's reputation and influence in the academy  to say nothing of his name recognition in the broader world of law and politics  have never rivaled those of his colleague. (Though 15 years younger than Rawls, Nozick died in the same year, 2002, after a long struggle with cancer.) Doubtless, part of the explanation is that Rawls's "left-liberalism" (as he later described his position) harmonizes far better with the typical orientation of the contemporary professoriat. In addition, unlike Rawls, Nozick never made the advancement of a particular political doctrine the unifying concern of his academic career. Rather, his wide-ranging intellect led him to follow "Anarchy" (his first book) with other works addressing a considerable variety of philosophical topics, ranging from free will to decision theory to (in his 1989 book "The Examined Life") love, death, faith, and the meaning of life.

More important, however, "Anarchy" never constituted a true alternative to Rawls's doctrine, since, on every substantive issue except the legitimacy of governmental redistribution of wealth, Nozick and Rawls agreed. (And even on that issue, in a passage typically ignored by his admirers, Nozick himself hedged.)

Like Rawls's "Theory," "Anarchy" opens with a sweeping statement of the primacy of justice  understood, in the latter book, as individual rights, defined as freedoms from external restraint over one's actions  over all other criteria for assessing political and social institutions. In other words, Nozick more or less retained Rawls's first principle (liberty) while eliminating the second (difference).

Suggesting that "the fundamental question of political philosophy" is not how government should be organized but "whether there should be any state at all," Nozick offers an adaptation of John Locke's doctrine that government is legitimate only to the degree that it affords greater security for life, liberty, and property than would exist in a chaotic, pre-political "state of nature." More emphatically than Locke, however, Nozick concludes that the need for security justifies only a minimal, or "night-watchman," state, since it cannot be demonstrated, he believes, that all rational individuals would find any more extensive government necessary to secure their rights.

In place of Rawls's "difference principle," Nozick propounds an "entitlement theory" of justice, according to which individual property holdings are justified only if they derive from just acquisitions or (voluntary) transfers. Remarkably, Nozick never spells out the criteria of just acquisition. However, instead of "current time-slice" views of distributive justice, like Rawls's, which assess current holdings according to some external standard of equity, Nozick asserts a "historical" standard, which determines the legitimacy of a distribution purely by whether it originated from a just procedure.

Nozick offers a witty and incisive critique of Rawls's rationale for his difference principle, refuting the implausible claim that merely because members of a society benefit from social cooperation, its less-advantaged members are automatically entitled to a share in the earnings of their more successful peers.

Yet Nozick's libertarianism, which compares income taxation to forced labor, suffers from a corresponding defect of its own. Nozick never acknowledges the need for a liberal regime to guarantee some level of social security and educational benefits to all citizens, to the extent its circumstances allow, if only to ensure the continued loyalty of the poor to that regime. Like Rawls, Nozick sought to impose an abstract vision of justice on political life, relegating considerations of feasibility (i.e., of conformity with the likely demands of actual human beings) to be resolved by others, in the spirit of Immanuel Kant's dictum, "let justice triumph, even if the world perishes by it."

Ironically, however, Nozick himself ultimately acknowledges that his entitlement theory is insufficient to refute demands for a redistributionist state, since it can never be demonstrated that existing holdings derive from an unbroken series of voluntary transfers: Doesn't every people's collective title to their land derive from some original act of unjust conquest? Hence, surprisingly, he ends up suggesting that something like Rawls's difference principle is morally required after all, in the name of "rectification," on the dubious premise that those currently least-well-off have the highest probability of being descended from previous victims of injustice.

This is not the only area of agreement between Nozick and Rawls. Like Rawls, Nozick insists that the justness of a society be assessed only by whether its procedures correspond to his preferred notions of justice, not whether it actually rewards morally worthy ways of life. Also like Rawls, Nozick ends his book by representing the just society as morally libertarian in the extreme, implicitly denying the legitimacy of laws prohibiting such practices as prostitution and the sale of addictive drugs.

Although he balanced his critique of the flaws he discovered in Rawls's theory with remarkable homage to its ostensible "beauty," Nozick was far brighter, and a much better and more thought-provoking writer, than his colleague. Unfortunately, he shared with Rawls a constricted view of political philosophy as an enterprise devoted to the production of abstract theories, with little or no regard for the grounding of justice in human nature. Those seeking an alternative to the shallow egalitarianism and moral libertarianism of our time would do far better to return to the thought of America's greatest statesmen, such as Lincoln and the authors of "The Federalist"; to the liberal philosophers who guided them, notably Locke and Montesquieu, and ultimately to the greatest classical philosophers, for all of whom political theorizing was inseparable from the quest for a serious empirical understanding of the human condition and the human good.

Mr. Schaefer is professor of political science at College of the Holy Cross and author of "Illiberal Justice: John Rawls Vs. the American Political Tradition."