Hayek on Mill: The Mill–Taylor Friendship and Other Writings by Friedrich Hayek, edited by Sandra J. Peart University of Chicago Press, 373 pp., $65.00

John Stuart Mill may well be the most important liberal thinker of the nineteenth century. In countless respects, his once-revolutionary arguments have become familiar, even part of the conventional wisdom. Certainly this is so for his great 1869 essay The Subjection of Women, which offered a systematic argument for sex equality at a time when the inferior status of women was widely taken for granted. It is also true for On Liberty, published in 1859, which famously argued that unless there is harm to others, people should have the freedom to do as they like. A strong advocate for freedom of speech, Mill offered enduring arguments against censorship. He also had a great deal to say about, and on behalf of, representative government.

Friedrich Hayek was the twentieth century’s greatest critic of socialism, and he won the Nobel Prize in economics. A lifelong defender of individual liberty, he argued that central planning is bound to fail, even if the planners are well motivated, because they cannot possibly assemble the information that is ultimately incorporated in the price system. Hayek described that system as a “marvel,” because it registers the knowledge, the preferences, and the values of countless people. Hayek used this insight as the foundation for a series of works on freedom and liberalism. Committed to free markets and deeply skeptical of the idea of “social justice,” he is a far more polarizing figure than Mill, beloved on the political right but regarded with ambivalence by many others. Nonetheless, Hayek belongs on any list of the most important liberal thinkers of the twentieth century.

Mill and Hayek help to define the liberal tradition, but in both temperament and orientation, they could not be further apart. Mill was a progressive, a social reformer, an optimist about change, in some ways a radical. He believed that, properly understood, liberalism calls for significant revisions in the existing economic order, which he saw as palpably unjust: “The most powerful of all the determining circumstances is birth. The great majority are what they were born to be.” Hayek was not exactly a conservative—in fact he was sharply critical of conservatism on the ground that it was largely oppositional and did not offer an affirmative position—but he generally venerated traditions and long-standing practices, seeing them as embodying the views and knowledge of countless people over long periods. Hayek admired Edmund Burke, who attacked the idea that self-styled reformers, equipped with an abstract theory, should feel free to override social practices that had stood the test of time. Mill had an abstract theory, one based on a conception of liberty from both government and oppressive social customs, and he thought that society could be evaluated by reference to it.

Against this background, there is every reason to be intrigued by…