Jeffrey Rosen is president and chief executive of the National Constitution Center and a law professor at George Washington University. His new book, “Conversations With RBG: Ruth Bader Ginsburg on Life, Love, Liberty and Law,” will be published in November.

The reputation of Justice Oliver Wendell Holmes, who lived from 1841 to 1935, has fluctuated along with the political and constitutional battles of every generation since he was appointed to the Supreme Court in 1902. At the beginning of the 20th century, Holmes was lionized as the greatest legal thinker of his time by progressives who celebrated his dissenting opinions arguing for the protection of free speech and the upholding of economic regulations. After World War II, he was criticized by Catholic legal scholars and civil-libertarian liberals who were alarmed to discover his enthusiasm for eugenics, which he displayed in upholding mandatory-sterilization laws. Christian theologians and conservative political activists denounced Holmes’s moral relativism in insisting that law could be separated from God’s will. More recently, Holmes has been out of fashion among both conservative originalists and progressive living-constitutionalists, who dislike his rejection of the idea that the Constitution contains absolute principles that can be invoked to protect minorities against mob rule.

In “Oliver Wendell Holmes: A Life in War, Law, and Ideas,” Stephen Budiansky sets out to revive Holmes’s reputation and relevance as a model of intellectual humility for our polarized age. And his readable, lively and engaging biography is so successful that it persuaded me, a Holmes skeptic, to give the Yankee from Olympus a second look. Budiansky emphasizes that Holmes learned from his service in the Civil War that moralism leads to intolerance — “when you know that you know, persecution comes easy,” he wrote. More than most judges, Holmes managed to set aside his prejudices and partisan loyalties because of his philosophical skepticism about the impossibility of ever being confident that one is right. “To have doubted one’s own first principles,” as he put it, “is a mark of a civilized man.”

This philosophical skepticism led him to uphold most laws against constitutional challenges; as he put it in his most famous dissenting opinion, “A constitution is not intended to embody a particular economic theory . . . it is made for people of fundamentally differing views.” The same philosophical skepticism, however, eventually persuaded him to write some of the greatest defenses of free speech of his time, on the grounds that a functioning democracy needs broad tolerance for what he famously called “the thought we hate.”

Holmes’s skepticism about absolute moral principles came from his time in the Union Army, where he was wounded three times and almost died at Antietam, the bloodiest battle in American history. Holmes took from his service in the Army, which Budiansky describes in vivid detail, the idea that fighting for ideals was senseless; as Louis Menand famously wrote, the war “made him lose his belief in beliefs.” The war made Holmes suspicious of moral certitude, zealotry and ideologues of the right and the left. “I don’t care to boss my neighbors and to require them to want something different from what they do,” he told Harold Laski, “even when, as frequently, I think their wishes more or less suicidal.” Holmes came to believe that life is a struggle and the only thing that can redeem it is ceaseless hard work — mastery of a subject, a discipline or a job for its own sake, without being able to control the result.

The subject Holmes chose to master was law, and he worked harder at it than anyone else of his generation. He told a cousin that he had resolved to write a classic work on the law before the age of 40 and that he hoped after that to become a Supreme Court justice. Holmes achieved both ambitions, writing a book, “The Common Law,” that revolutionized legal thinking by arguing that judges made policy rather than simply applying the law, and that rather than embodying absolute moral principles, law reflected changing social norms.

This view, which conservatives today denounce as sociological jurisprudence, led Holmes to a constitutional philosophy not of judicial activism but of radical judicial restraint. In his two decades as a judge in Massachusetts, he voted to strike down a law as unconstitutional only once. A constitution, he wrote, “is a frame of government for men of opposite opinions and for the future, and therefore [we should] not hastily import into it our own views, or unexpressed limitations derived merely from the practices of the past.” He followed the same philosophy on the U.S. Supreme Court, asking not whether the Constitution specifically authorized the federal or state governments to act but whether it specifically forbade them from doing so. He rejected the idea of the conservative textualists and originalists of his day, who argued that the Constitution should be strictly enforced according to its original public meaning. In his view, they were simply substituting their own political preferences and ascribing them to the Constitution’s framers.

Holmes’s radical devotion to judicial restraint led him to vote to uphold not only progressive economic legislation but also some of the most illiberal laws of his day, including mandatory-sterilization laws and laws disenfranchising African American voters in the Jim Crow South. But he was not indifferent to all violations of constitutional rights. In 1914, he began to write the dissents that would define his judicial legacy, and they included cases where Holmes was outraged by what he viewed as clear violations of the rule of law by racist mobs. In the Leo Frank case, in which a Jewish factory manager was almost certainly wrongly convicted of murdering a 13-year-old factory worker in Atlanta, Holmes dissented from the Supreme Court’s refusal to review the case. “Mob law does not become due process of law by securing the assent of a terrorized jury,” Holmes wrote. His warning against “lynch law” administered by a jury or “by a mob intent on death” was vindicated when Frank was, in fact, lynched by an anti-Semitic mob.

And then there are Holmes’s free-speech dissents, in particular his shining dissent in Abrams v. U.S. (1919), which ranks with Louis Brandeis’s concurring opinion in Whitney v. California (1927) as one of the greatest defenses of the need to protect free speech in American history. While Brandeis emphasized his faith that truth would emerge from thoughtful deliberation, Holmes emphasized what Budiansky calls “the importance of tolerance for opposing views, not just as a bedrock foundation of democracy but as a reflection of fundamental skepticism about certainty.” “Certitude is not the test of certainty,” Holmes wrote in developing his mature view on free speech. “We have been cocksure of many things that were not so.”

The most inspiring sign of Holmes’s intellectual humility was that, throughout his long life, from his 20s through his 90s, he never stopped cultivating his faculties of reason and set aside time every day for learning. At age 21, he began keeping a list of every book he read for pleasure and self-improvement. At the time of his death, the range was inspiring — more than 4,000 books, ranging from philosophy, sociology, religion, economics and science to murder mysteries. In the course of reading more than a book a week, he had a rule that a book had to be finished once started, no matter how arduous.

Today, when progressives, conservatives and libertarians are all turning to the courts to overturn the judgments of legislatures, and when Twitter mobs on the right and the left attack each other with the moralistic certainty that Holmes deplored, Holmes’s intellectual humility, and his willingness to question even his own deeply held premises — he called them his “can’t helps” — are humbling and inspiring. And at a time when progressives and conservatives alike are so sure of their own premises that America is more polarized than at any time since the Civil War, the “skeptical humility,” as Budiansky puts it, that Holmes took from the war seems more elusive, and more urgently needed, than ever.

Oliver Wendell Holmes

A Life in War, Law, and Ideas

By Stephen Budiansky

579 pp. $29.95