The Utilitarian philosopher John Stuart Mill was a 24-year-old bachelor when he met Harriet Taylor in 1830. She was a 23-year-old wife, the mother of two small children. Their attraction to one another was immediate, and the relationship developed into a grand passion. Eventually her husband, John Taylor, demanded that Harriet break off all contact with Mill, but she flatly refused. Instead, she went to Paris, where Mill had arranged to join her. Away from London society, they had their Define the Relationship talk. Even then the situation was still retrievable, but in France they made the fatal decision: their relationship would be a chaste one.

As men of the cloth are wont to do, Harriet's pastor, the Reverend W. J. Fox , felt it was his duty to rebuke her for setting a bad moral example: she and Mill, the minister of South Place Chapel pontificated, ought to have the common decency to let love win and forthrightly set up house together. Mill had to write to this popular London preacher and guiltily explain that although they would defy his pastoral counsel he still hoped that Fox would not despair of his soul: "I know you disapprove & cannot enter with the present relation between her & me & him, but a time perhaps is coming when I shall need your kindness more than ever."

Mill's friend, the budding sage Thomas Carlyle, was all ready to settle down into some good-natured gossiping, but when the sordid reality dawned on him, he was truly scandalized. In letter after letter he confided in hushed tones the horrid truth: "I do believe the whole thing is strictly Platonic still!" Carlyle eventually decided that Mill was slowly killing himself through this unnatural commitment to celibacy: "His eyes go twinkling and jerking with wild lights and twitches; his head is bald, his face brown and dry." (This is a description of Mill when he was barely 30 years old!)

John Taylor lived for another 16 years, and during all that time Harriet's relationship with Mill never became a physical one. The Taylors had had another child shortly after Harriet first met Mill, and her decision for chastity was based on the Utilitarian principle of the greatest happiness for the greatest number: "I should spoil four lives & injure others." Indeed, although Harriet and John Taylor were now merely Seelenfreudin (soulmates) as well, she never formally separated from her husband, retained genuine affection for him, sought to do her social and practical duties as a wife and mother, and, when John Taylor was struck down by cancer, nursed him devotedly during the gruesome last three months of his life.

As an empirical philosopher, John Stuart Mill was preoccupied with precise and accurate definitions. In his celebrated A System of Logic (1843), he even included an entire chapter which sought to define "definition." Nevertheless, he found, to his deep frustration, that the most important relationship of his life could not be defined and therefore could not be spoken of and therefore did not have a social existence. Celibacy is the love that dares not speak its name. When confronted by his father about his relationship with Harriet, Mill replied that "he had no other feelings towards her, than he would have towards an equally able man." This statement hardly accords with his letters to her, in which he would address her as "She to whom my life is devoted"; "O my own love"; "my only & most precious"; and so on.

But what to call it? One acquaintance settled on a "violent friendship." You could fill a whole book with the names of the widely known lovers of fashionable Victorian married ladies and gentlemen. Despite (perhaps even because of) their reputation for respectability, the Victorians knew how to accommodate a good, old-fashioned sexual affair: it could even make one more popular in society.

Some things, however, are so perverse as to be beyond the pale, and unrepentant chastity is a prime example. Harriet and Mill found themselves social outcasts, walled off into a private world all their own. And, of course, our own age is even more prudishly disapproving: of all the types of sexual deviants who offend against modern sensibilities, few are more viscerally abhorrent than the celibates. The philosopher Jo Ellen Jacobs became the leading expert on Harriet, even editing The Complete Works of Harriet Taylor Mill (1998). Doing her best to defend her subject, Jacobs (without any direct or compelling evidence) put forward a theory that John Taylor infected Harriet with syphilis, and that this must have been the real reason why she and Mill did not have sex: it was reassuring to imagine that Harriet had not brazenly chosen celibacy, but merely acquiesced in the interests of public health.

Nevertheless, Mill and Harriet stubbornly refused to accept how shameful chastity is. Freethinkers though they were, they comforted each other with the biblical truth that "to the pure all things are pure." They protested that there was another way to have a passionate relationship which was not imaginable to "sensualists." Once they were married, they worked together on Mill's autobiography, which they arranged to have published posthumously. Harriet insisted that they should just defiantly acknowledge their twenty long years in the Victorian chastity underworld: "This ought to be done in its genuine truth and simplicity—strong affection, intimacy of friendship, & no impropriety. It seems to me an edifying picture for those poor wretches who cannot conceive friendship but in sex—nor believe that expediency and the consideration for feelings of others can conquer sensuality."

The details of this indescribable relationship were first aired in a book published in 1951, John Stuart Mill and Harriet Taylor: Their Correspondence and Subsequent Marriage, by F. A. Hayek, who would go on to win a Nobel Prize in Economics. It has now been republished, along with ten occasional pieces (one previously unpublished) and some correspondence, as Hayek on Mill: The Mill-Taylor Friendship and Related Writings.

Harriet's relations and descendants could never quite bring themselves to expose this platonic relationship to public view. Her last surviving grandchild died in 1939. Hayek on Mill attests to Hayek's heroic efforts during World War II to track down all the surviving Mill correspondence, much of which had been haphazardly scattered across the globe. The direct results of Hayek's dedication to this task were the first scholarly biography, Michael St. John Packe's The Life of John Stuart Mill (1954), and the 33 volumes of The Collected Works of John Stuart Mill (John M. Robson, general editor). Hayek himself had the privilege of cherry-picking the correspondence between Mill and Harriet. Determined to let this seemingly sui generis relationship speak for itself, Hayek put so many of their letters to each other into the heart of John Stuart Mill and Harriet Taylor that it sometimes feels like one is reading an epistolary novel.

As if it were not bad enough that they refused to make their relationship sexual and thus comprehensible, Mill added offense to offense by praising Harriet's intellect extravagantly. Although he had known many of the great men of his age, Mill insisted in both public and private, year upon year, that Harriet was "the profoundest thinker & most consummate reasoner I had ever known." The Great Men, of course, assumed that this judgment was "sheer delusion."

It particularly got up people's noses that Mill and Harriet, cocooned in their John Lennon-Yoko Ono relationship, manifestly felt no need for anyone else's society. Indeed, the letters are laced with their contempt for every eminent Victorian in sight. The French thinker Auguste Comte was a "dry sort of man," barely even worth refuting; J. G. Holyoake, the leader of the Secularist movement, was "this foolish creature"; Archbishop Trench was "that base & imbecile animal"; the celebrated historian T. B. Macaulay was "an intellectual dwarf"; Thomas Carlyle and Alexis de Tocqueville are dismissed in one sweep as "weak in moral, narrow in intellect, timid, infinitely conceited"; and even Queen Victoria herself is pronounced to be a "great baby."

Despite their withdrawal into their own private world, Mill longed for the public to know of Harriet's genius. During their long, chaste affair, she had worked closely with him on the book that was published to wide acclaim as Principles of Political Economy (1848). They hatched a plan that he would dedicate it to her, but when she solicited her husband's opinion he replied that, since she had asked, he thought it would demonstrate "a want of taste & tact which I could not have believed possible." They compromised by pasting the dedication into a select number of gift copies. In perfect tragicomic propriety, she is referred to as "Mrs. John Taylor." Mill asserted in this wordy, convoluted dedication that Harriet, of all the people he has ever known, had "the most eminently qualified" mind to speculate on such matters.

Mill had a disquieting sense that people would not be convinced, but the only way he could think to compensate for this was to keep churning out encomiums in ever more startling language until, in Harriet's gravestone inscription, he more or less claimed that if she had lived she could have brought in the millennium ("the earth would already become the hoped-for heaven").

Hayek himself shocked readers by insisting that Harriet had been a major shaper of the thoughts of the brilliant John Stuart Mill. Maybe it is now time for everyone to learn how to forgive Mill for flagrantly choosing celibacy, for wantonly admiring Harriet's intellect, and for shamelessly being influenced by her opinions.

Timothy Larsen is McManis Professor of Christian Thought, Wheaton College. His sixth monograph, The Slain God: Anthropologists and the Christian Faith, was published by Oxford University Press in 2014.

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