A friendship is a relationship without ceremony. Unlike marriage, friends don’t announce their commitment to each other before an assembly of loved ones. If a friendship ends, it’s likely to do so unceremoniously. Friends may never even directly discuss the painful decision to extract themselves from the other’s life, let alone fight for the relationship to survive. They can simply explain to themselves and others, “We grew apart.”

At each step of their decade-long friendship, Ann Friedman and Aminatou Sow refused to accept the norm that a close friendship is expendable and peripheral to adult life. They named each other as emergency contacts and got matching tattoos. When years of physical distance and miscommunication left them feeling estranged from each other, they signed up for couples therapy. Their friendship, they insisted, was “too big to fail.”

In their vibrant book, “Big Friendship: How We Keep Each Other Close,” Friedman, a journalist, and Sow, a digital strategist, seek to give friendship the serious treatment they believe it deserves. The mission to elevate the status of friendship has been central to their popular podcast, “Call Your Girlfriend,” and their efforts led journalist and author Jill Filipovic to deem the pair in her 2017 book, “The H-Spot,” “Modern feminism’s grandes dames of female friendship.”

After Friedman moved across the country, she and Sow started the podcast to keep up with each other’s thoughts on politics and pop culture — the twin interests that drew the women together when they met as recent college graduates in D.C. An episode is likely to feature a conversation about police abolition, an interview with Hillary Clinton or a commentary on reality TV.

The same wit and chatty style of the podcast infuse the book. A hybrid of memoir, cultural criticism and advice, “Big Friendship” describes experiences that are common in deep friendships but rarely acknowledged. For instance, Friedman and Sow explain that they “have changed each other in countless ways,” so much so that they have trouble remembering who they were before they met because it’s now “impossible to untangle us.” In their first encounter, they write, “we began the process of making each other into the people we are today.”

Friedman and Sow have long felt that they’ve “lacked a vocabulary for the dynamics and milestones and ups and downs of our relationship.” This linguistic drought — a reflection of the scant attention friendship is paid compared with romantic and familial relationships — extends to the type of friendship Friedman and Sow have. The authors dismiss expressions like “best friend” or “BFF” because they “don’t capture the adult emotional work we’ve put into this relationship”: the work of keeping the friendship afloat from a distance, tending to the relationship when Sow was weighed down by an undiagnosed chronic illness, navigating the tripwires in an interracial friendship (Friedman is White; Sow is Black). “Big Friendship” is their neologism for an enduring, life-altering relationship like theirs.

“Big Friendship” is dappled with novel terms and concepts for common tensions in friendships. The terms would have been useful for Friedman and Sow to have had when their friendship was sputtering. Without the language to pinpoint their problems, they couldn’t spot, for instance, the dynamic of withdrawing from a friend even as they longed to restore closeness. Like a doctor trying to diagnose and treat an unnamed illness, Friedman and Sow were at a disadvantage in identifying or solving what ailed their friendship. It was only with the help of their couples therapist and their research for this book that they could see and repair what had gone wrong. After a linguistics scholar told them about the concept of “complementary schismogenesis,” Friedman and Sow had language (albeit clunky) for why they’d fallen into a feedback loop of misunderstanding: They had reacted to their divergent ways of communication by ramping up the aspects of their different styles.

What most distinguishes this book from other recent writing on friendship is Friedman and Sow’s keen analysis of how politics figures into the practice of friendship. Whereas we have no say in the family that raises us or where we grow up, we get to choose our friends. Those choices, Friedman and Sow argue, “say something about the kind of world you want for yourself.” For instance, a White person may profess anti-racism, but if there’s not a trace of melanin among her close friends, her behavior indicates otherwise. In friendships, the personal is political.

In this way, “Big Friendship” recalls a declaration by literature scholar Phyllis Rose in her study of Victorian marriages, “Parallel Lives.” Rose writes that marriage is “the primary political experience in which most of us engage as adults” because spouses must regularly negotiate power and inequalities. Friedman and Sow’s account suggests that Rose’s argument can apply to close friendships as well. In a bracing chapter on the threats to intimacy in interracial friendships, the authors conclude that such friendships stretch both parties, but asymmetrically. The White person will learn about a life experience outside her own; the person of color may feel burdened by being enlisted as a “personal racial-education service,” or stung by feeling reduced to a stereotype.

The authors also encourage readers to carry out feminism within friendships. Friedman and Sow note that women and other marginalized people often buy into a scarcity mind-set, believing that there are limited slots for those who look like them. The authors call on women to follow what they’ve deemed “Shine Theory”: to channel feelings of competition against other women into support; to share power rather than hog it. It’s an idea that they first laid out in 2013 and that now permeates pop culture. In 2018, after Rep. Alexandria Ocasio-Cortez praised Rep. Ayanna Pressley on Twitter, Pressley thanked her for “living #shinetheory out loud.”

“Big Friendship” arrives in a world destabilized by a global pandemic, financial insecurity and flagrant racism. These are what Friedman and Sow call the “hurricanes of life,” against which friendship is a “real-deal insurance policy.” But we have to pay into insurance before we can draw on it. “Big Friendship” is the guide we need to make that investment.

Big Friendship

How We Keep Each Other Close

By Aminatou Sow and Ann Friedman

Simon & Schuster.

232 pp. $26