By Elijah Anderson

Flash mobs have reappeared on the streets of Center City. These groups of mostly black youths gravitate to a designated location at an appointed time. Once there, they become a mob that gathers force as it roams the streets, wreaking havoc on businesses while terrifying and sometimes attacking pedestrians.

As quickly as these storms appear, they're over. But the effects are lasting, powerfully rending the diverse, civil public spaces we might call cosmopolitan canopies.

Historically, despite William Penn's vision of a City of Brotherly Love that accepts all kinds of people, most Philadelphians have lived in racial and ethnic enclaves. This segregation persists today.

Yet Center City is dotted with cosmopolitan canopies such as the Reading Terminal Market and Rittenhouse Square. These are usually calm and relatively pleasant places where a diverse mix of people go about their business, at times self-consciously on good "downtown" behavior. They come to "know" each other without having met, and they can be helpful to complete strangers. Such settings, which no one group expressly owns but which all are encouraged to share - situated under a protective umbrella, or canopy - are a special type of urban space that every visitor seems to recognize, appreciate, and enjoy.

The canopy allows people who identify strongly with class or ethnic groups to work toward a more cosmopolitan appreciation of difference. They discover people who are strangers not just as individuals, but also as representatives of other groups. The canopy can thus be a profoundly humanizing experience.

As canopies proliferate, their qualities become elements of the city. The resulting social sophistication helps diverse people get along.

After violent incidents such as the recent flash mobs, the canopy must recover its reputation as an oasis of comity. Media coverage of these events is unrelenting. As a result, young black men become more defined as people to fear, even though the mobs may be sprinkled with whites. People warily watch for those who might engage in this sort of activity; the figures that readily come to mind are young, black, and male.

These disturbing incidents reinforce the profoundly negative reputation of the iconic ghetto. For many Philadelphians, black and white, the black ghetto invokes what the sociologist Everett Hughes called a "master status," which defines a person regardless of individual characteristics. For many, especially whites, black male strangers are the chief symbols of the ghetto. When encountered in public, their master status - their race - supersedes all other characteristics.

The young black man starts at a deficit: He must prove himself to be trustworthy, which he is seldom able to do to the satisfaction of his white counterparts in the short time allowed. So they opt to distance themselves from him.

From time to time in the city, young black males make the news by committing dramatic crimes that shock both blacks and whites, as with the flash mobs. Despite frequent reports of mayhem in the ghetto, the crimes that most upset the city's collective conscience might be called "racial crossover" crimes, in which a white person is the victim of a black perpetrator. Philadelphians take notice, and the stereotype of the dangerous young black man becomes more salient. The victim, a white person who was minding his or her own business, is regarded as particularly undeserving of this fate.

What responsibility do those who interact under the canopy have for ensuring it covers everyone, and for extending it across the city? Keeping an open mind means giving others the benefit of the doubt. It means trying to make others comfortable rather than withdrawing. And it requires treating what happens under the canopy not as "time out" from life, but as a model for it. Ultimately, lessons learned under the canopy can be carried into neighborhoods across the city.

Philadelphia's canopies do not yet encompass the whole city or all its people. Much of it remains segregated, reinforcing boundaries. And even under the canopy, those personifying the ghetto are often met with suspicion. A more inclusive civility that extends beyond the magical but bounded canopies requires changing what transpires in neighborhoods and workplaces as well as in public.

The canopy offers a taste of how inclusive and civil we can be. Even amid bad news, it speaks to the positive possibilities of urban life.