As reliably as autumn brings Orion to the night sky, spring each year sends a curious constellation to the multiplex: a minor cluster of romantic comedies and the couples who traipse through them, searching for love. These tend not to be people who have normal problems. She is poised, wildly successful in an ulcer-making job, lonely. He is sensitive, creative, equipped with a mysteriously vast apartment, unattached. For all these resources, nothing can allay their solitude. He tries to cook. She collects old LPs. He seeks love in the arms of chatty narcissists. She pulls all-nighters in her office. Eventually, her best friend, who may also be her divorced mother, tells her that something needs to change: she’s squandering her golden years; she’ll end up forlorn and alone. Across town, his stout buddy, who is married to someone named Debbee, rhapsodizes about the pleasures of cohabitation. None of this is helpful. As the movie’s first act nears its end point, we spy our heroine in the primal scene of rom-com solitude: curled up on her couch, wearing lounge pants, quaffing her third glass of wine, and excavating an enormous box of Dreyer’s. She is watching the same TV show that he is (whiskey half drained on his coffee table, Chinese takeout in his lap), and although this fact assures us of a destined romance, it is not so useful for the people on the screen. They are alone; their lives are grim. The show they’re watching seems, from the explosive flickering, to be about the invasion of Poland.

Today, half of U.S. residents are single, and a third of all households have one occupant. Illustration by Jean-François Martin

Few things are less welcome today than protracted solitude—a life style that, for many people, has the taint of loserdom and brings to mind such characters as Ted Kaczynski and Shrek. Does aloneness deserve a less untoward image? Aside from monastic seclusion, which is just another way of being together, it is hard to come up with a solitary life that doesn’t invite pity, or an enviable loner who’s not cheating the rules. (Even Henry David Thoreau, for all his bluster about solitude, ambled regularly into Concord for his mother’s cooking and the local bars.) Meanwhile, the culture’s data pool is filled with evidence of virtuous togetherness. “The Brady Bunch.” The March on Washington. The Yankees, in 2009. Alone, we’re told, is where you end up when these enterprises go south.

And yet the reputation of modern solitude is puzzling, because the traits enabling a solitary life—financial stability, spiritual autonomy, the wherewithal to buy more dishwashing detergent when the box runs out—are those our culture prizes. Plus, recent demographic shifts suggest that aloneness, far from fading out in our connected age, is on its way in. In 1950, four million people in this country lived alone. These days, there are almost eight times as many, thirty-one million. Americans are getting married later than ever (the average age of first marriage for men is twenty-eight), and bailing on domestic life with alacrity (half of modern unions are expected to end in divorce). Today, more than fifty per cent of U.S. residents are single, nearly a third of all households have just one resident, and five million adults younger than thirty-five live alone. This may or may not prove a useful thing to know on certain Saturday nights.

Eric Klinenberg, a sociologist at New York University, has spent the past several years studying aloneness, and in his new book, “Going Solo: The Extraordinary Rise and Surprising Appeal of Living Alone” (Penguin), he approaches his subject as someone baffled by these recent trends. Klinenberg’s initial encounter with the growing ranks of singletons, he explains, came while researching his first book, about the Chicago heat wave of 1995. During that crisis, hundreds of people living alone died, not just because of the heat but because their solitary lives left them without a support network. “Silently, and invisibly, they had developed what one city investigator who worked with them regularly called ‘a secret society of people who live and die alone,’ ” Klinenberg writes.

“Going Solo” is his attempt to see how this secret society fares outside the crucible of natural disaster. For seven years, Klinenberg and his research team interviewed more than three hundred people living alone, plus many of the caretakers, planners, and designers who help make that solitary life possible. Their sample included single people in everything from halfway hotels to elder-care facilities, and drew on fieldwork conducted primarily in seven cities: Austin, Texas; Chicago; Los Angeles; New York; San Francisco; Washington, D.C.; and Stockholm.

The results were surprising. Klinenberg’s data suggested that single living was not a social aberration but an inevitable outgrowth of mainstream liberal values. Women’s liberation, widespread urbanization, communications technology, and increased longevity—these four trends lend our era its cultural contours, and each gives rise to solo living. Women facing less pressure to stick to child care and housework can pursue careers, marry and conceive when they please, and divorce if they’re unhappy. The “communications revolution” that began with the telephone and continues with Facebook helps dissolve the boundary between social life and isolation. Urban culture caters heavily to autonomous singles, both in its social diversity and in its amenities: gyms, coffee shops, food deliveries, laundromats, and the like ease solo subsistence. Age, thanks to the uneven advances of modern medicine, makes loners of people who have not previously lived by themselves. By 2000, sixty-two per cent of the widowed elderly were living by themselves, a figure that’s unlikely to fall anytime soon.

What turns this shift from demographic accounting to a social question is the pursuit-of-happiness factor: as a rule, do people live alone because they want to or because they have to? At one point, Klinenberg suggests that living alone provides “restorative solitude”; it may be “exactly what we need to reconnect.” But most of the people he introduces seem neither especially restored nor vigorously connected. They are insecure, proud of their freedoms but hungry for contact, anxious, frisky, smug, occasionally scared—in short, they experience a mixture of emotions that many people, even those who do not live alone, are apt to recognize.

Take, for example, Kimberly, a New Yorker who’s in the film business, and who underwent a sort of crisis when she found herself past thirty and living alone. She threw herself into her work, but at night she numbed herself with epic sessions of TV. “It took me a long time to figure out that it wasn’t gonna happen the way it happened in college,” she tells Klinenberg. “People didn’t just drop by.”

Things changed when she made the decision to buy an apartment, committing to a future alone. She renovated, began hosting parties, went freelance, tried Internet dating, and made contact with Single Mothers by Choice, a support organization for unattached women hoping to raise a child. Was this self-realization or resignation? Kimberly confesses, “I didn’t want to hang curtains by myself. I’d always thought I would do it with a partner and a lover.” Yet autonomy as an ideal brought her happiness, she says, partly because it freed her from the shame of falling short.

Some people remain single out of a disinclination to settle. Elsewhere, we meet Justin, a young man who came to New York out of college and moved in with friends after he found that living alone made it hard to meet people. The less Justin relied on his roommates for social entrée and domestic support, though, the more they seemed to get in the way, imposing on his space, his privacy (“When you bring a girl home, not only will the girl notice your roommates, but your roommates will notice her”), and his capacity to live as he pleased. He’s been alone since.

Most people who were brought up in the past half century have been taught to live this way, by their own rules, building the world they want. That belief—Klinenberg calls it “the cult of the individual”—may be the closest thing American culture has to a common ideal, and it’s the premise on which a lot of single people base their lives. If you’re ambitious and you’ve had to navigate a tough job market, alone can seem the best way to approach adulthood. Those who live by themselves are light on their feet (they’re able to move as the work demands) and flexible with their time (they have no meals to come home for). They tend to be financially resilient, too, since no one else is relying on their income. They are free to climb. To a particular kind of hyper-ambitious young person, entering into a domestic commitment too early carries a risk: what if you end up yoked to somebody who lacks the stamina to keep up? “For a rising generation of aspiring professionals, the twenties and early thirties is precisely not the time to get married and have a family,” Klinenberg observes.

Klinenberg’s research suggests that our usual perceptions about life alone get things backward. Far from being a mark of social abandonment, the solo life tends to be a path for moving ahead, for taking control of one’s circumstances. And, rather than consigning individuals to suffer in their solitude, aloneness may come at a cost to the community. The single life is inherently self-interested: it calls for vigilance on matters of self-preservation both large (financial autonomy) and small (dish detergent), and, in many cases, it frees the solitary from the sorts of daily interaction that help craft a sense of shared responsibility.

For one person, that may be a good deal. But, multiplied across a population, it becomes problematic. In a landmark study, “Bowling Alone” (2000), the Harvard political scientist Robert D. Putnam noted a puzzling three-decade decline in what he called “social capital”: the networks of support and reciprocity that bind people together and help things get done collectively. His work considered the waning of everything from P.T.A. enrollment to dinner parties and card games, but the core of his argument was declining civic participation. Between 1973 and 1994, the number of people who held a leadership role in any local organization fell by more than half. Newspaper readership among people under thirty-five dropped during a similar period, as did voting rates. Why? Putnam pointed to cultural shifts among the post-Second World War generation; the privatization of leisure (for example, TV); and, to a smaller extent, the growth of a commuting culture and the time constraints of two-career, or single-parent, family life. “Older strands of social connection were being abraded—even destroyed—by technological and economic and social change,” he wrote.

Putnam, in other words, saw public institutions as a casualty of the same forces of individuation driving modern aloneness. And, unlike Klinenberg, who’s optimistic about solo life largely because he’s optimistic about the socializing effects of technology, Putnam believed that digital communication offers too weak a connection to reverse the loss of community skills. Good socialization is a prerequisite for life online, not an effect of it, he pointed out; without a real-world counterpart—the possibility of running into Web friends “at the grocery store”—Internet contact gets ranty, dishonest, and weird. What’s more, “real-world interactions often force us to deal with diversity, whereas the virtual world may be more homogeneous.” People lose the habit of reaching out to build bridges when they’re most needed. Technology may help us to feel less lonely, but it doesn’t really make us any less alone.

“Bowling Alone” appeared more than a decade ago—an eternity in technology years. And yet the intervening time has, if anything, intensified Putnam’s concerns. A couple of recent books re-articulate them for the Facebook age. One of these, “Alone Together: Why We Expect More from Technology and Less from Each Other” (2011), by the M.I.T. psychologist Sherry Turkle, takes issue with the basic promises of digital connection. She thinks that togetherness, far from being strengthened by technology, has been crowded out by “the half-light of virtual community.”

Turkle is an unlikely candidate for this genre of techno-skepticism. Two of her previous books, “The Second Self” (1984) and “Life on the Screen” (1995), looked to a future of digital connection. Since then, though, her enthusiasm has foundered. Today, she’s unsettled by kids who text in lieu of making phone calls, by adults who answer e-mail during lectures, by Furbies, and by a recent book called “Love and Sex with Robots.” She thinks that technology is simultaneously drawing us away from social fulfillment and keeping us from finding solace in being alone. “To experience solitude you must be able to summon yourself by yourself,” she writes. “Many find that, trained by the Net, they cannot find solitude even at a lake or beach or on a hike.”

Turkle’s research assumes that connecting through technology is, essentially, a choice. But what’s the alternative? There’s a wistfulness in her plea for face time that runs through several studies of this kind. In “Together: The Rituals, Pleasures, and Politics of Cooperation” (Yale), Richard Sennett argues that coöperation is a skill—one that, until recently, all adults were forced to learn. Now that we’re losing challenging, diverse forms of interaction in the workplace and at school, he worries, we’re growing up without this training. “A distinctive character type is emerging in modern society, the person who can’t manage demanding, complex forms of social engagement, and so withdraws,” he writes. It’s a compelling model, but a limited one—what if Sennett is simply looking for coöperation in the wrong places? “Together” is a book about messy, productive collaboration that makes no mention anywhere of Wikipedia.

Given our digital habits, the question isn’t whether we should use technology to ease our loneliness. It’s how. One day this past October, a New Yorker named Jeff Ragsdale, recently dumped and down on his luck, taped a flyer around Manhattan. It read, “If anyone wants to talk about anything, call me.” He included his cell-phone number. Within a day, he had received about a hundred calls and text messages. When people started posting pictures of the flyer on Reddit.com, the social-news Web site, that number jumped to seven hundred calls and a thousand text messages daily. The best—and worst—of these have been collected in a new book, “Jeff, One Lonely Guy” (Amazon), edited by David Shields and Michael Logan. Jeff’s contacts are variously melancholy (“I’m the Minister of Depression”), engaged (“I don’t fall in love. I love jazz”), and perplexing (“I went through a traumatic breakup. Now I want to work in finance”). But there’s an undertow of pathos that often comes starkly to the surface, as here:

Dad beat me, my sister, and my mom, and he finally got arrested. He went to prison and a mental institution. . . . I went through a bunch of foster homes. . . . He tried to contact me on Facebook, but I didn’t respond. . . . I tried to kill myself at 17 with an overdose of sleeping pills. The ambulance took me away.

Or here: