These are, in some ways, very good times for the Bechdel test. Recent movies have offered up nuanced, celebratory portrayals of women’s friendship. Recent TV shows have provided pairings of friends—Abbi and Ilana, Meredith and Cristina, Lucca and Maia, Leslie and Ann, Hannah and Jessa, Pennsatucky and Big Boo—whose friendships have taken on the tensions that Hollywood has traditionally reserved for romantic couplings. Books, too, in both fiction and nonfiction, have considered—and in many ways re-considered—the female friendship. Rebecca Traister’s All the Single Ladies, Kate Bolick’s Spinster, and Jill Filipovic’s The H-Spot have all made cases that American culture, and indeed American politics, should find ways to institutionalize the female friendship, giving good friends the same kinds of benefits that have traditionally come with marriage.

Their arguments are politically complicated, but otherwise extremely elegant. After all, as Deborah Tannen puts it in her new book You’re the Only One I Can Tell: Inside the Language of Women’s Friendships, “Having a friend means feeling less alone in the world.”

Tannen, a professor at Georgetown University, is a linguist (specifically, she is an expert in the field of interactional sociolinguistics, which emphasizes the case-study method to study language as it’s used in real-life contexts), and her latest book functions in one way as a language-oriented supplement to all these other current explorations of women’s friendship. The book is by turns fascinated with friendship and frustrated by it. (As to the latter, Tannen points out that, according to a Carnegie Mellon study, negative social encounters with their friends raised women’s blood pressures, while leaving men’s unaffected.)

You’re the Only One I Can Tell—the title comes from a phrase many young girls utter to each other, and a sentiment that is replicated, figuratively if not literally, throughout their lives—is on the whole a thorough exploration of the way women, across ages and races and classes and geographies and gender identities, relate to each other. In it, Tannen has put to use her typical methodology, arriving at the book’s insights through interviews, literature reviews, anecdotes, and her own experience as a woman and a friend. Most strikingly, though, the linguist’s latest book explores the same thing those current works of pop culture imply, as well: the notion that friendship and romance are not as mutually exclusive as American culture has portrayed them to be. That the language of romance can mirror the language of friendship—and vice versa. The book’s title, after all, also evokes the stuff of romantic love, and of traditional monogamy, and of soul mates: You’re the Only One.

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Romance is what it is, in literature and in life, in large part because of the conflicts it represents. There is passion colliding with reason, most stereotypically—the heart wants what it wants—but there is also, even more importantly, the known colliding with the unknown: Does he return your feelings? Will she say yes? Do they still love you, after all these years?

These are precisely the tensions, You’re the Only One I Can Tell suggests, that can animate women’s friendships: Friendships, like romance, can be fraught because of the same interplay between confidence and confusion that can make romance both exciting and, occasionally, excruciating. Does she like me? Will she call me back? Does she still love me, after all these years? Tannen tells the stories of women who have spent years mourning lost friendships, and, too, of women whose friendships have seen them through marriages and children, joys and losses—that have, indeed, brought a new meaning to the term “‘til death do us part.” The love in the platonic relationships Tannen describes, just like their romantic counterparts, can be passionate, and comforting, and life-defining, and occasionally heart-breaking.

And also: confusing. A recurrent theme of You’re the Only One I Can Tell is the extent to which misunderstandings can both complicate friendship and, in the rough manner of romance, make it more exciting. One of Tannen’s core concepts in it, adapted from the linguist Robin Lakoff’s notion of “communicative style,” is the “conversational style”—the “how” of language that complements the “what.” Conversational style, Tannen notes, can involve the tone of voice one uses to speak, and the pitch of speech, and the volume, and the distance one keeps from one’s conversational partner, and whether one interrupts or lets pauses linger, and whether one communicates directly or indirectly (“Does it seem cold in here to you?” versus “Could you turn down the AC?”)—and the many, many other choices people make when they engage in conversation.

And in much the same way that, for example, love languages can help or hinder the compatibility of romantic partners, conversational styles can create, by turns, friction and interest in platonic pairings. While talking, one friend might interject often, her way of indicating engagement (a high-involvement style of conversation); her conversation partner, though, who prefers a high-considerateness style, might bristle at the interruptions. One friend might make her opinions known indirectly; the recipient of those opinions might consider that approach to be a little bit, or a very lot, passive-aggressive. One friend, believing in bluntness, might comment on her friend’s weight gain; that friend, believing in tact, might be offended.

And on and on. “‘Do unto others as you would have others do unto you,’” Tannen notes of the old adage—“if your conversational styles differ, what you would have others do unto you may be the very thing that bugs them when you do it unto them.” And that extends beyond conversation itself to broader assumptions about what should shape platonic interactions and relationships. If a friend is going through a hard time, what is the best way to comfort her—to talk directly about the problem, or to distract her from it? If a friend gets a bad haircut, should that be acknowledged or ignored? They’re small questions, in one way, whose answers will be determined in part by cultural differences and assumptions (Americans, Tannen points out, tend to be much more blunt than people in other countries); they’re also big ones, though, that come down to the personalities of the friends in question.

And they are, too, questions that suggest how fundamentally fragile friendship can be—and how much patience and work can be required of friendships that hope to last in the long term. The cliché, at least the one suggested in the pop culture that preceded the relatively Bechdel-friendly offerings of the current moment, has been that female friendships are reliable and, above all, easy: comforting and constant, as women have gone about the (passionate, exhilarating, occasionally painful) search for their romantic partners. The women of Sex and the City occasionally argued, sure, but their ecosystemic purpose—to be there for their friends as they date and search and marry—was always extremely clear. “Dreams change, trends come and go,” Carrie muses, “but friendships never go out of style.”

Here, though, via a book about language, is a subtle challenge to that idea: Friendships, in Tannen’s treatment, are comforting, yes, and constant, ideally, but definitely not easy. Many of the friendships Tannen considers in the book—her own, occasionally, but most often the ones lived by the women she interviews—are ones that have ended, for both grand and petty reasons. And the ones that carry on do so in part because the people in them have committed to their upkeep—to overcome the differences of perspective and action that might otherwise make them fraught.

You’re the Only One I Can Tell is a somewhat unlikely sequel to Tannen’s first book, 1990’s You Just Don’t Understand, her treatise on the differing communicative styles between women and men. (In it, Tannen made the observation that has now become the stuff of sitcom truism: that men, when navigating the world, are uniquely—and extremely—reluctant to ask for directions.) There have been many books in between, to be sure; You’re the Only One I Can Tell, however, is a book about friendship that is also interested in the miscommunication that can so complicate it. “Avoiding Conflict—and Escalating It” is one chapter subhead. “It’s How I Feel When I’m With You” is another. “Like Family—For Better, for Worse” is another. The language, in this book about language, is saturated with concepts that apply equally well to romance in its more traditional forms. The language, too, celebrates friendship in its frustrations and its rewards and, above all, its wonderful complexity. It is promoting friendship from a supporting character into a starring role.

A few years ago, the writer Emily Rapp argued that “friendships between women are often the deepest and most profound love stories, but they are often discussed as if they are ancillary, ‘bonus’ relationships to the truly important ones.” They are still, too often, discussed in that way. But not always. Not anymore. And here, through Tannen’s consideration of the communication that informs those relationships, is further evidence of that. The loves that the linguist explores in her romantically named book are not merely ones that comfort and sustain women until, one day, the real thing comes along. They are the real thing.