Romantic friendship is a term historians use to describe a recognized form of intense, affectionate, sometimes physically expressive relationship between people of the same sex that flourished in the eighteenth and nineteenth centuries, particularly in the anglophone world. It was not a subculture, not a secret, and not confined to people we would now identify as gay or lesbian. It was mainstream, and it was considered honorable.

The relationships took different forms. Women wrote to women in language that sounds, to twenty-first century ears, indistinguishable from love letters. They described themselves as "wedded" to their friends, swore undying devotion, shared beds as a matter of course, and grieved their separations with intensity that their families validated and recorded. Men did this too — perhaps with somewhat less frequency, but the phenomenon was not exclusively female. Walt Whitman wrote poems about male comradeship (calamus love) with a physical warmth that his contemporaries found moving rather than suspicious. Daniel Webster wrote to a male friend that he had shed tears on the road to Boston, thinking of their separation.

What made this possible? Historians disagree about emphasis. Carroll Smith-Rosenberg's influential 1975 essay argued that nineteenth-century gender arrangements — the strict separation of male and female social worlds — drove women into intimate female networks as a matter of structural necessity. Women's lives were organized around other women: they prepared each other for childbirth, nursed each other's sick, kept each other company across the long separations marriage might impose. The intensity of these bonds was not aberrant; it was the expected output of the system.

Lillian Faderman, writing in 1981, extended this analysis and argued that romantic friendships were not perceived as sexual by their participants or observers because the nineteenth century largely did not have a concept of female sexuality that extended beyond heterosexual reproduction. Women simply were not thought to have the kind of active sexual desire that could be directed toward other women in a problematic way. The innocence of the friendships was, in part, a function of this conceptual vacuum.

The historical question of whether romantic friendships were "really" sexual — whether the women (and men) involved experienced them erotically — is in some respects unanswerable and in other respects misframed. The question smuggles in a modern insistence on categorization (was this "really" friendship or "really" love?) that the nineteenth century did not apply. The better question is what romantic friendship did — what it provided, what it meant, what it made possible — and what changed when the concept became unavailable.

What changed was the emergence of a medical and psychological discourse around sexual inversion and homosexuality in the last quarter of the nineteenth century. The sexologists (Krafft-Ebing, Havelock Ellis, later Freud) created a vocabulary and a framework that made intense same-sex attachment legible as a symptom or an identity. Once that framework existed, the old innocence was no longer available. The behaviors that had been "romantic friendship" could now be read as signs of pathology. The space contracted. The freedom that had existed in the absence of a category was foreclosed by the category's arrival.

What romantic friendship demonstrates, most clearly, is that the organization of intimacy is contingent. The lines we now draw — between friendship and love, between affection and desire, between appropriate and suspicious — were not always drawn where they are now, and were not drawn by nature.