I find myself pondering a lunchtime talk I heard yesterday by Chris Leinberger, the developer and New Urbanist thinker who's currently involved in recreating downtown Albuquerque. It wasn't anything factually new in his speech that struck me--it was the tone of unalloyed optimism about downtowns in general and their future.

176192_6712_1 Leinberger sees all the signs as positive: In the 1980s, he estimates, there were probably four indisputably healthy and vibrant downtown areas in America: midtown Manhattan, the Michigan Avenue "Gold Coast" in Chicago (pictured here), Back Bay in Boston, and the area around Nob Hill in San Francisco. Now, Leinberger says, there are many more: Seattle, Portland, San Diego, Denver and perhaps a dozen others have become Class-A downtowns.

Even more remarkable, from his perspective, is the number of big-city downtowns that were utterly dead two decades ago--Newark, Baltimore, Cleveland--and now have sizeable residential populations and unmistakable signs of commercial life. In the past five years, he says, even downtown Detroit has ceased to be the basket-case most outsiders assume it to be.

One needn't accept every detail of this argument. A Newark or a Cleveland can look encouraging or depressing, depending on what angle you're viewing it from. But there's obviously some reality to the inner-city comeback Leinberger and others are talking about.

What interests me is that all this enthusiasm is coming to the surface at the same moment that a whole different crew of thinkers is promoting a much more pessimistic theory. According to their line of argument, downtowns are acquiring a patina of entertainment glitz and sophistication, but beneath the bright lights lurks systemic pathology: high crime rates, bad schools, strapped budgets, and high tax rates that are driving businesses out to the periphery.

Moreover, the downtown population gains of the 1990s have mostly melted away, they weren't very large anyway, and most important, they haven't included more than a tiny number of middle-class families. It's all singles, childless couples and empty-nesters, and the singles and the couples will move out to the suburbs when they start to have children. You can't build an urban revival on that sort of basis.

This is the argument that Joel Kotkin makes in his widely quoted new book, The City , and it's the opposite of Leinberger's view in every possible respect. They can't both be right. Or maybe they can. Perhaps the whole dispute is mostly a matter of definition.

Kotkin sees downtowns as they existed a half-century ago and says those will never exist again. That's true, of course. Leinberger sees a 21st-century downtown that doesn't perform the traditional functions but is growing ever more skillful at finding new ones. If I interpret him correctly, he's saying that a central city inhabited largely by young couples and empty-nesters can still be a magnet for stable and reassuring human relationships, and that if we insist on lamenting the absence of downtown, circa 1950, we'll never grasp the importance of what's beginning to happen.

It may be a close question, but I think Leinberger has the better of the argument.