It is a hard thing, being right about everything all the time. Nobody likes a know-it-all, and we wait for the moment when the know-it-all is wrong to insist that he never really knew anything in the first place. The know-it-all, far from living in smug superiority, has the burden of being right the next time, too. Certainly no one has ever been so right about so many things so much of the time as John Stuart Mill, the nineteenth-century English philosopher, politician, and know-it-all nonpareil who is the subject of a fine new biography by the British journalist Richard Reeves, “John Stuart Mill: Victorian Firebrand” (Overlook; $40). The book’s subtitle, meant to be excitingly commercial, is ill chosen; a firebrand should flame and then die out, while Mill burned for half a century with a steady heat so well regulated that it continues to warm his causes today—“Victorian Low-Simmering Hot Plate” might be closer to it.

Mill credited his lover, Harriet Taylor, as the co-creator of his best-known works. Illustration by Ralph Steadman

Mill believed in complete equality between the sexes, not just women’s colleges and, someday, female suffrage but absolute parity; he believed in equal process for all, the end of slavery, votes for the working classes, and the right to birth control (he was arrested at seventeen for helping poor people obtain contraception), and in the common intelligence of all the races of mankind. He led the fight for due process for detainees accused of terrorism; argued for teaching Arabic, in order not to alienate potential native radicals; and opposed adulterating Anglo-American liberalism with too much systematic French theory—all this along with an intelligent acceptance of the free market as an engine of prosperity and a desire to see its excesses and inequalities curbed. He was right about nearly everything, even when contemplating what was wrong: open-minded and magnanimous to a fault, he saw through Thomas Carlyle’s reactionary politics to his genius, and his essay on Coleridge, a leading conservative of the previous generation, is a model appreciation of a writer whose views are all wrong but whose writing is still wonderful. Mill was an enemy of religious bigotry and superstition, and a friend of toleration and free thought, without overdoing either. (No one has ever been more eloquent about the ethical virtues of Jesus of Nazareth.)

All of which makes trouble for a biographer. Every time we turn a corner, there is Mill, smiling just a touch too complacently at having got there first. Admiration for intelligence and truth easily turns into resentment at the person who has them; Aristides the Just was banished from Athens because people were fed up with hearing him called Aristides the Just. It is one of the many virtues of Reeves’s funny, humane biography that it brings Mill to life in the only way sententious great men can be brought to life, and that is by showing us what he was like when he lost his heart and when he lost his reason. Both happened to him just once, but that was sufficient. Mill’s is a story of a man out in the pure sun of reason and rational inquiry, lit at night by the romantic moonlight of a little bit of love and just enough madness.

Mill’s boyhood was one of the strangest of the nineteenth century, and is one subject of his own matchless memoir, published posthumously. He was born in 1806 to a driven Scottish writer, James Mill, and a passive and mostly invisible mother. Chosen for an experiment in education, he was crammed with learning by his father and his father’s mentor, the utilitarian philosopher Jeremy Bentham. The aim was to produce a mind distended out of all proportion—force-fed facts, as unlucky geese are force-fed corn. The foie gras of the boy’s mind was then to be dined on by a grateful nation; the boy’s life, like the goose’s comfort, was secondary. Latin, Greek, ancient history, political economy: “By the age of six,” Reeves notes, “young Mill had written a history of Rome; by seven he was reading Plato in Greek; at eight soaking up Sophocles.” By twelve, he more or less sat his examinations for university entrance.

The curriculum had no room for new poetry, and not much for old music. It was nothing but history, math, economics, the classics, and the Benthamite axioms: actions could lead to pleasure or pain, happiness or distress, and the right action was the one that led to the most happiness for the most people. In hard hands, the principle could seem like a mechanical parody of ethics, but it had its points. Bentham’s real achievement was to squeeze the piety out of Enlightenment talk of “rights.” People didn’t have rights because their creator endowed them with rights; they had them because rights were useful to have.

Mill’s odd education became one of the nightmares of the nineteenth century; in “Little Men,” Louisa May Alcott imagines a child who is so stuffed with learning by an ambitious father that he blows his circuits and becomes permanently feebleminded. But Mill emerged as the prodigy he was meant to be. At the age of seventeen, he became a clerk at the East India Company, the private corporation that then ran India, and remained at its headquarters in London for thirty-five years, administering Indian affairs at a distance—a servant of British imperialism, but a benevolent kind. (When, later, the government tried to cut funds for Indian colonial colleges teaching Arabic and Sanskrit, Mill fought to keep the practice going, for fear of losing all contact with the élites. “Without knowing the language of a people, we never really know their thoughts, their feelings, and their type of character,” he wrote.) He was such a demon for work that, growing overheated through feverish memo-writing, he would gradually strip off his clothes and work gravely at his stool without waistcoat or pants, as his colleagues watched in prim Victorian wonder.

More important for his thought, Mill became, before he was twenty, a popular writer out on the radical edge of journalism. He plunged into the new world of professional writing in newspapers and magazines that was as much a part of the early Victorian scene as the booming railroad. He became a leading contributor to, and by far the most effective polemicist for, the Westminster Review, which Bentham had started in 1823 as a counterpart to the conservative Quarterly Review and Edinburgh Review. “Journalism is to modern Europe what political oratory was to Athens and Rome,” the young Mill announced grandly. While some of the great minds of the previous century, Samuel Johnson most memorably, had begun as journalists, where the money was, and had been promoted in the popular mind to the dignity of philosophers, Mill began in philosophy, where ideas were found, and chose to write for the magazines and papers, where the fighting was.

Through the eighteen-twenties, Mill attacked David Hume’s history (Hume, though philosophically radical, was politically conservative), William Cobbett’s sentimental populism, the false idea of “balance” in the British constitution (if a government was indeed perfectly “balanced,” then “the machine must stand still”), and discrimination against Catholics. In all of it, he was still following his mentors’ ideas, and affecting his mentors’ chilly mien. “The description so often given of a Benthamite, as a mere reasoning machine . . . was during two or three years of my life not altogether untrue of me,” he confessed much later.

Reasoning machines, as we all know, have a high failure rate; sooner or later, the hard drive just stops spinning. Mill’s did, too: in 1826, he was plunged into a black depression. His description in his memoir of his breakdown, which lasted for about two years, is among the best in English: “I sought no comfort by speaking to others of what I felt. If I had loved anyone sufficiently to make confiding my griefs a necessity, I should not have been in the condition I was.” Though he was able to continue working, he could no longer write. With his quick intelligence, he recognized that the problem lay somewhere in his formation, in things that had been given too little attention. He turned to music for solace. It helped for a while, until he grew obsessed with the thought that there are only so many notes, and so many combinations of notes, and that, sooner or later, they would be used up, and all melody exhausted.

Poetry saved him. He read the early romantics, Coleridge and Wordsworth in particular, and by the end of the decade was cured, or at least better. He began to see a new light. It couldn’t change his affect: he remained a tight, mild, buttoned-down man. But it changed his affections. From that time on, he was as evangelical for the arts as any Ruskinian. (“He was most emphatically a philosopher, but then he read Wordsworth,” a disappointed utilitarian friend remarked in 1840.) He toured Italy regularly, making rounds of the churches to see the pictures. He became an aesthete—a dutiful and systematic one, but an aesthete all the same.

His love of poetry and music and art also led him toward conservative thought. Aesthetes always bend to the right, in part because the best music and the best buildings were made in the past, and become an argument for its qualities. Someone entering Chartres becomes, for a moment, a medieval Catholic, and a person looking at Bellini or Titian has to admit that an unequal society can make unequalled pictures. To love old art is to honor old arrangements. But even new and progressive art is, as Mill knew, a product of imagination and inspiration, not of fair dealing and transparent processes; the central concerns of liberalism—fairness, equity, individual rights—really don’t enter into it. Mozart, whom Mill loved, would have benefitted as a person had he lived in a world that gave him the right to vote for his congressman, collect an old-age pension, and write letters to the editor on general subjects, and that gave his older sister her chance at composing, too. But not a note of his music would have been any better. Art is a product of eccentric genius, which we can protect, but which no theory of utility can explain.

So when, in 1834, Mill—having been chastened by madness and instructed by art (and having mourned, and been emancipated by, the death of Bentham, two years earlier)—began a new journal, the London Review, the contributor he sought most eagerly was no utilitarian but the great Scottish reactionary prose-poet Thomas Carlyle. (The keen friendship between these two utterly unlike men would itself be a good subject for a book.) Mill revered Carlyle’s originality of vision and soul, while Carlyle, though he mocked Mill’s pensive faith in rational argument, recognized that the younger man had the far more finished and exact mind. The friendship survived even the most scarifying incident in the history of letters, when Mill’s housemaid accidentally burned the only manuscript of Carlyle’s history of the French Revolution in the kitchen fire. (Carlyle was goodhumored about it, perhaps because, like many writers, he really preferred having the project to brood on to the brief melodrama of publication.) Throughout the eighteen-thirties, the give-and-take between Carlyle’s deeply pessimistic sense of the primal violence that lay beneath the surface of civilization and Mill’s insistence that the cure for the primal illness was more civilization was one of the creative engines of English thought.

Beginning in the late eighteen-twenties, Mill took on a great deal of Continental philosophy that, then as now, was regarded as just this side of charlatanism by his bread-and-butter Anglo-Saxon colleagues. He borrowed the term “self-development” from the German Romantic philosopher Wilhelm von Humboldt, and considered that, rather than utilitarian pleasure, to be the end of life. A good life for Mill, post-madness, is not one where you have queued before the slot machine of utility and got the candy it dispenses. It is one where you have gone out into the world to build the best self you can—travelled where you wanted and seen what you could and said what you had to, sung your own songs and heard your own poems. Mill was a romantic and an epicurean in a gray tweed suit, and his mature liberalism is both what a narrow historian means by liberalism—a theory of free conduct justified by its good results—and what the rest of us mean when we say that someone is liberal-minded: open to all the pleasures of life and generous in their enjoyment.

Like every intelligent Englishman of an epicurean cast, he spent as much time as he could in France. Though he was quietly Francophile from early on, his illness and recovery made him declaratively so. He bought a little house in the papal town of Avignon, in the South of France; it became the home of his heart, where, in his later years, he lived and wrote, and where, eventually, he died. He always condescended to the French, as even Francophile Englishmen will: “Whenever anything goes amiss, the habitual impulse of French people is to say, ‘Il faut de la patience’ ”—One must be patient—“and of English people, ‘What a shame.’ The people who think it a shame when anything goes wrong—who rush to the conclusion that the evil could and ought to have been prevented, are those who, in the long run, do most to make the world better.” The hopes that had been raised and then ruined by the 1848 revolution in France played the same role for Mill’s generation that the fall of the Iron Curtain and the rise of Putin have played in our time: inspiring proof that liberalism might win after all, followed by the crushing realization that it was no match for authoritarian, strongman nationalism, which, in France, took the form of the papier-mâché emperor Louis-Napoleon. (The French experience burned Mill badly. It led him, for a while, to propose, in the ideal republic, giving educated voters more votes than uneducated ones—it was a nation of peasants who had voted in Louis-Napoleon.)

Yet France, even after Mill’s disappointments with its politics, remained for him the great good place. The humanizing influence of French civilization—“the free and genial atmosphere of Continental life,” as he called it—tempered his drier certainties. The mature Mill is a stable thinker but not a systematic one. He recognizes the existence of half-truths alongside near-truths, and of “almost so”s right by “yes, nearly”s. “Truth, in the great practical concerns of life, is so much a question of the reconciling and combining of opposites,” he once wrote. “Even progress, which ought to superadd, for the most part only substitutes, one partial and incomplete truth for another.”

Throughout the thirties and forties in early-Victorian England, no one was more attended to than the radical Mill. We can only envy his public, for he would have been a terrible pundit for our sound-bite age. He isn’t an aphorist; his stuff takes space. Mill’s sentences sway and ponder with the heavy grace of elephants, and are often about the same size. Defending a philosophy of hedonism, he writes sentences that contain more philosophy than hedonism: “The happiness which they meant was not a life of rapture; but moments of such, in an existence made up of few and transitory pains, many and various pleasures, with a decided predominance of the active over the passive, and having as the foundation of the whole, not to expect more from life than it is capable of bestowing.” “Gather ye rosebuds while ye may,” in other words, but no rosebuds fall on the page. Whatever the subject, Mill surveys the ground, clears it of underbrush, builds a house of straw to demonstrate what a shoddy house looks like, sets it on fire, and in its place builds a house of brick, which he dares you to knock down. The house of brick is, as Victorian brick houses usually were, lacking in grace and lightness and charm, but it still stands. You don’t come away from Mill dazzled, as you do with Ruskin or Carlyle, but you come away with a place to live your life.

Mill had an allergy to dogma, including his own—which makes him an occasional friend to the dogmatist. When someone says that proof of God’s existence can be found in Nature, he doesn’t say it’s bosh. He asks what this would actually entail if it were true, and infers that such a creator would have to be limited, inept, well-meaning, forgetful, and in a daily contest with another power: “A Being of great but limited power . . . who desires, and pays some regard to, the happiness of his creatures, but who seems to have some other motives of action which he cares more for, and who can hardly be supposed to have created the universe for that purpose alone.” What natural theology, taken seriously, shows is not the great Watchmaker or the All-Seeing Jove but the absent-minded Landlord, a sort of eternal Lord Emsworth, who, though he helps the young lovers, cares mainly about his pig.

But Mill really means it: take the argument for God’s existence seriously, and that’s where it leads you. That’s the key thing about Mill, hustling between London and Avignon, climbing mountains and administering India and surveying churches: he always really means it. When, in the eighteen-sixties, the English-appointed governor of Jamaica punished a native uprising with hideous cruelty—the accused were tortured and many hanged, after trumpery trials—Mill led the fight in England against him, chairing a committee to have him tried not for maladministration but for murder. (A committee formed in defense of the governor included Dickens and Carlyle.) When Mill said that his rights were worthless unless everyone else had them, too, he really meant it. His friendship with Carlyle broke only when the Scotsman’s racism became too much for Mill, a passionate abolitionist, to bear.

Of all Mill’s causes, his championing of the rights of women is still the most heroic, and its heroism turns out to be rooted in a passionate love for another person. Mill said that he had always been a feminist, but there isn’t any doubt that the engine of his feminism was his friend, love, collaborator, and eventual wife, Harriet Taylor. They met at her home, in Finsbury, in the summer of 1830, over dinner among liberal friends. Harriet, a year younger than Mill, was married, to a slow-witted, well-meaning pharmacist named John Taylor; they had two children. She was smart and pretty—“a small head, a swan-like throat, and a complexion like a pearl,” the daughter of someone present at the momentous dinner wrote later—and already oppressed by her very unequal marriage. If you see her pictures, and make allowances for the cosmetic conventions of the portraiture of the time, she still looks pretty wonderful: big Natalie Portman eyes and that fine long neck. She and Mill fell for each other quickly, and began working together. Within a year, someone was writing to her to ask, of a new review of Byron, “Did you or Mill do it?”

For the rest of the decade, theirs was a complicated lobster quadrille of love. If the lovers were just a touch less fierce-looking, Mill and Taylor would make as good a Victorian love story as Robert Browning and Elizabeth Barrett. They were seen everywhere together. Carlyle’s wife, Jane, gossiped that “Mrs. Taylor, tho’ encumbered with a husband and children, has ogled John Mill so successfully that he was desperately in love.” After years of intrigue, the Taylors finally decided on a separation. To test Mill’s love, Harriet went to Paris, and invited him to spend six weeks with her there. The interlude was splendid—but then Harriet, with a rather sweet imperiousness, allowed her husband to come to Paris for his own audition. Harriet ultimately decided—with mingled propriety, uncertainty, and something like flirtatiousness—that they could share her, on an alternating schedule, at the Taylor house, her husband entertaining guests with her on some days, and Mill on others. Taylor paid the bills, while Mill stocked the wine cellar. When John and Harriet were pining for each other, they held secret meetings at the London zoo, by the cage of their “old friend Rhino,” whose horn—as they perhaps knew, perhaps did not—was an Asian agent of erotic love.

The gossips gossiped all the more. The gawking Carlyle reported that in France they had “eatin’ grapes off o’ one bunch, like two love-birds.” Though in his memoir Mill denied that they had had sex before they were married, there are purring letters that suggest the contrary. “While you can love me as you so sweetly & beautifully shewed in that hour yesterday, I have all I care for or desire,” he wrote in one letter. “The influence of that dear little hour has kept me in spirits ever since.” An earlier biographer of Mill, Bruce Mazlish, makes the point that Mill’s mother was the real missing presence in his life, and that Harriet (as Yoko Ono did for John Lennon) helped fill his need for a woman who was both an intellectual match and thoroughly maternal. The romance in Mill’s life helped turn him from a thinking machine into a feeling mensch; the know-it-all became an anything-for-love.

Harriet’s own writing of the eighteen-thirties and forties on the oppression of marriage has the urgency of immediate experience. A smart woman who had been obliged to be someone’s idea of a wife, she had been at that table with the dumb little dictator: “The most insignificant of men, the man who can obtain influence or consideration nowhere else, finds one place where he is chief and head. There is one person, often greatly his superior in understanding, who is obliged to consult him, and whom he is not obliged to consult. He is judge, magistrate, ruler, over their joint concerns.” Mill and Taylor, in their later writing, most famously in the 1869 “The Subjection of Women,” aren’t content to show that women would be happier if freer; they go right to the ground and ask what reason we have for thinking that any restraint on women’s freedom is just. The arguments against women’s liberty have to do with what is natural for women to do, or what women are capable of doing, or what some men would be offended by. They take each case and show that its only rationale is our slavery to custom. Women are naturally passive? Go tell Queen Elizabeth. They are happy in their lot? All slaves say as much to the slave master. They are “designed” to have children? No argument from nature can ever alter an argument from ethics: if women want to raise children, excellent; if they don’t, there is no natural reason to think they must any more than there is a reason to think that male philosophers should all put down their pens and go out hunting for mammoths.

Mill makes the point again and again that no one can possibly know what women are or are not “naturally” good at, since their opportunities have been so vanishingly small compared with the length of their oppression. Arguing against the notion that women have no talent for the fine arts, Mill makes the shrewd point that in the one liberal art where women are encouraged as much as men, acting on the stage, everyone admits that they’re just as good or better. In any case, nature has nothing to do with what should be done. In his essay on “Nature,” he writes, “Nature cannot be a proper model for us to imitate. Either it is right that we should kill because nature kills; torture because nature tortures; ruin and devastate because nature does the like; or we ought not to consider what nature does, but what it is good to do.” Mill’s rejection of a natural case isn’t that anything goes; it’s that nobody can really know what goes until someone goes farther. He doesn’t believe in a blank slate on which anything can be inscribed; he believes in the power of the chalk-holding hand to change the sum on the blackboard.

On a list of modern words that changed the most lives, those which Harriet and John wrought together in “The Subjection of Women” must rank high. Before it, women were for all intents and purposes chattel; afterward, they would sooner or later have to be made citizens. You could argue against it, try to unmake it, but you couldn’t ignore it. The beach was taken, and the cautious odd couple by the rhino’s cage had taken it.

John and Harriet’s intellectual idyll was long-lived in shadow, short-lived in sunlight. Mr. Taylor died in 1849, and in 1851 John and Harriet were married. But after only seven and a half years Harriet died of one of those sad, unnamed wasting diseases that blighted the period. Mill had a monument—of the same Carrara marble as Michelangelo’s David—constructed for her in Avignon, with an inscription that included the lines “Were there but a few hearts and intellects like hers / this earth would already become the hoped-for heaven.” That same month, Mill sent off to the publisher the finished manuscript of “On Liberty,” dedicating it to the memory of “the friend and wife whose exalted sense of truth and right was my strongest incitement.” (Darwin was finishing “On the Origin of Species” that same year, and also saw it published the next; the two books remain the bedrock of the liberal age.)

Reeves rightly calls “On Liberty” “the greatest celebration of the value of human freedom ever written.” Mill has a principle of liberty, but far more important is that he starts a practice of liberal thought. The utility principle is installed, as one might install a piece of software, but is employed only fitfully. No shrewd new proof is proposed. It is the negative side of Mill’s claim that changes everything. He reverses figure and ground in the argument. When he asks us to think about liberty, he doesn’t want us to ask, Can this odd thing people are doing be deduced from some ethical axiom that lets me call it “good,” and permits them to go on doing it? He wants us to ask something simpler: Is this practice causing me any real harm? Not potential harm to my feelings, not social harm to my idea of right, not damage to the great precepts of religion or to my stuffy uncle’s sense of propriety. Unless the speaker is actually about to cut your throat, you have to let him work his jaw.

And, by really meaning it, this essentially conservative and tradition-loving man showed that all kinds of practices can stand scrutiny and not be damaged, and that the authoritarian position is not the strongest one but merely the most frightened. Nothing is worse for being looked at. No idea is good enough to exist unopposed. Fundamental differences lie even at the heart of religion and must be freely aired. Christianity is not against argument; it is an argument—should one follow the Greek morality of St. Paul (which includes slavery) or the Jewish morality of St. Mark (which implies the Seder)? The usual objection to Mill’s argument is that free societies will still differ radically about what they want to be free for: my idea of fun is not yours, or Genghis Khan’s. Mill knew this—he knew that you couldn’t prove that good things were good. But he also knew that questions not decidable by proof were still amenable to argument, and that he would rather have the side of the argument that suggested that health, prosperity, and pleasure were good things than the side that said they weren’t.