by JULIET WATERS

We first meet Ethan Watters in the studio of Good Morning America, about to be interviewed on the new term he coined in an article for the New York Times Magazine. Problem is he's not sure how to define his new term, "urban tribes." A self-described "reluctant trend setter," he's sweating over whether or not he's going to make any sense. Personally, I'd be sweating over the prospect of a hundred thousand people thinking, "Trend? Haven't you noticed Friends is in its last season?"

Fortunately, before throwing Urban Tribes back into the slush pile I skipped to the epilogue where we find Watters on his honeymoon in Hawaii. "I have spent exactly twenty years," he writes, "living outside a family unit. It's hard not to look for a message in such a fact. One thing is clear: it is impossible to see such a large chunk of time (what will likely turn out to be more than a quarter of my life) as a transitional phase between youth and adulthood. Twenty years is an era - a goddamned epoch of one's existence."

If Watters has detected a trend, it's the trend of no longer seeing delayed marriage and family as a trend. What used to be called young adulthood is getting longer and longer, as urbanites increasingly hit middle age before they settle down and start families. Backlash against this reality is inevitable. Smug editorialists have been suggesting for years that this period of open-ended friendship and community is a rut, not a groove. It's the reason why women in their 30s and 40s are finding themselves alone and couples are finding themselves barren. No good can come, the dire warnings tell us, from a good time that might last 10 to 20 years.

Essentially, Watters' book is a counter-argument. From his own experience and a lot of casual research he concludes that urban tribes can nurture the kind of life experience that makes better partners, better parents, and better people ultimately. His argument, however, is pretty theoretical, since he's only recently married and is expecting a child. As a result this book is largely a nostalgic, somewhat idealized narrative of urban tribes from across the spectrum in the '80s and '90s. From Burning Man to dot-com lofts to junior-banker BBQs, he explores happy single life in the post-Mary Tyler Moore era.

At the same time, it's not all dancing with torn sheets in the rain. There are potential ruts, which Watters travels as well. Tribes can nurture self-esteem and self-reliance. They can also nurture drug addiction and denial and, frankly, loneliness. Who hasn't encountered a Queen Bee situation, where a strong woman resents and alienates the potential new girlfriends of her male tribesmen? Who hasn't met a Cockblocker, that guy who comes on so strong to any new girl who enters a tribe that he virtually guarantees the single life for all his friends? In one particularly instructive and insightful anecdote, Watters shows how a tribe, in its zeal to discourage a female member from continuing a bad relationship, ends up pushing her even farther into the arms of an abusive boyfriend. Sure it's great to have those friends who are always there for you break-up after break-up - until you realize that the day will probably come when you'll be breaking up with them too. Cutting ties with a friend you've had a few years can be painful. Dumping, or being dumped by friends you've had for decades can be traumatic.

Ultimately Watters is a soothing voice in the wilderness, but he is a traditionalist. His tendency to assure us that this is probably all leading up to marriage and family eventually will be irritating to anyone whose life isn't necessarily going there. Still if you're trying to figure out whether your tribe is a rut, a groove, or something you even want at all, Watters' book is a reasonably helpful start.

Urban Tribes by Ethan Watters, Bloomsbury, hc, 213pp, $24.95