He was a celebrity among the titled and the fashionable, but his particular appeal for women had a more solid cause. James understood women almost better than we understand ourselves: in Isabel Archer in The Portrait of a Lady he redefines a "lady" as a woman who can face up to an imprisoning marriage through an inward freedom to choose her path; in Catherine Sloper in Washington Square, he created a plain young woman who survives with dignity a bullying father and a captivating fortune-hunter; and in Milly Theale, he invented a woman who can transform a low plot to gain her fortune into a drama of her own which opens up a rare form of love at the end of The Wings of the Dove. Other perceptive men have shown us women such as Anna Karenina and Emma Bovary who are victims of their passions, but James shows us unfamiliar possibilities; not women as we are, but as we might be.
The insights didn't come just from intuition. James involved himself with two women who lived - precariously - on the evolutionary frontier. One was an ambitious writer, Constance Fenimore Woolson, great-niece of James Fenimore Cooper - privately, James called her "Fenimore". Among her works are three extraordinary stories of artists which precede James's pre-eminence in that genre. In fact, he took from her his title for the short story "The Figure in the Carpet", as well as the idea for "The Beast in the Jungle", a tale in which an ageing man fails to recognise a commanding experience for which he has waited all his life. Fenimore disarmed James with self-effacement, while her fictions challenged his scorn for women writers. She soothed editors with modest letters which went out of their way to stress how inferior was the lot of a single woman who must write for a living to that of a cherished wife. It is uncertain to what extent she believed this in the loneliness she certainly endured, but her best stories question marriage and feminine dependence. Her 14-year tie with James is filled with mystery: they had a pact to destroy their correspondence and kept their reunions secret: a shared house outside Florence in 1887, a spell in Geneva in 1888, and four days in Paris in the summer of 1893.
Fenimore's roaming life, her trophies of "Europe", and the psychological home she offered the expatriate in James, provided a model for the independent traveller, Maria Gostrey, in The Ambassadors. "You've recognised me - which is rather beautiful and rare," Maria remarks to the Jamesian man as they stroll along the old wall of Chester with its gaps and dips. "You see what I am."
Fenimore, who met James in 1880, was the second of the potent women in his life. The first was his orphaned cousin Minny Temple, who at 16 cut off her hair. "Could no one wrest the shears from her vandal hand?" asked Henry's brother William, excited by the bared contour of Minny's neck even as he called her "insane". Their mother deplored an unpolished girl who defied the norm of inanimate ladyhood and laughed in an open-mouthed way, showing all her teeth. But to Henry she was a free spirit, an "experiment of nature". In April 1863, when he was 20 and she 18, he asked her to tell him about a woman "body and mind". She confided to a friend: "I told him loads."
So, Minny and her unrealised dreams (one, a dream of joining James in Rome) became the prime source for his forward American girl. In 1870, after her death from tuberculosis at the age of 24, James promoted her to "pure fellowship" with his future thoughts and fancies, given her power to suggest "the reach and quality and capacity of human nature". In the same way, the Jamesian woman "affronts her destiny" when Isabel Archer turns down an English lord, the plum of romance. ("If she would not do this," Isabel thinks, "then she must do great things, she must do something greater.") The dying Milly Theale finds greatness through an act of generosity to a man who has not granted the experience she craves, but instead has made up to her with an eye to her fortune. All the same, as an evolving Jamesian man, he has the "reach" to meet her, after her death.
James, too, understood women better after their deaths. Fenimore's sudden death, when she fell or threw herself from a Venetian window in 1894, shocked James with a realisation that he, the master of the inward life, had failed to know a woman with whom he had been "extremely intimate". Her death exploded the comfy story he had told himself about "an angel of quiet virtue" who reserved for him her "infinite charity". Why was he convinced that it was suicide? What was the truth behind this woman's death? Why did James journey from London to her "death-house" in Venice and spend five weeks sorting her "things", and what do we make of his story of a surreal scene on the lagoon when he tried to drown her dresses and they came up around him like "black balloons"? And why, too, as an old man in 1914, did James not include Minny's dying pleas to him in his radiant memoir of her as the "heroine of the scene"? These are questions to do with living women before they became the material of art. James "preyed upon living beings", as Eliot recognised. To do this, he did involve himself (contrary to the legend of the detached master), but in the end his involvements were for readers, for us, and only in passing for women whose need for reciprocity remained active. Miss Loring, the companion of his sister, Alice, recalled his "horror of having responsibility about himself or his friends". For this reason, he was in his element with those who had died.
After Fenimore's death, James stayed in her rooms in Venice and Oxford where he set down his outline for "The Altar of the Dead", about a man who "cherishes for the silent ... dead, a tenderness in which all his private ... need finds a sacred, and almost secret expression". A year later he devised another tale in which a woman, so freshly dead that she still vibrates with human need, seeks out a man she has failed to meet in life. It's the start of a posthumous affair: she gives him back "passion for passion". These are ties more intimate than sex, leading to "inconceivable communion".
Alone, it seems, Minny Temple and Constance Fenimore Woolson were bold enough to cross the uncrossable boundary of "the private life" - James's phrase for the creative life. In doing so, they took him beyond the Woman Question of their age (issues of the vote and education in the 19th century; the issue of professional advance in the next century) to what is yet to come. Virginia Woolf said in 1915 it would take six generations for women to come into their own. If so, we're not there yet. Our unresolved future makes James increasingly pertinent, more than ever our contemporary as the 20th century recedes, now, into the past.
Lyndall Gordon's A Private Life of Henry James is published on Thursday by Chatto and Windus, pounds 20.