What's a good place to go to ward off a mood of depression? I don't know the answer to that question, but Petula Clark had a solution many years ago:

"When you're alone and life is making you lonely," she sang, "you can always go — downtown. … No finer place for sure, downtown. Everything's waiting for you." That song sold 3 million records in the United States in 1965.

What's interesting is the moment when Downtown became a smash hit: In 1965, American downtowns were at a kind of tipping point. Some of their 1950s vitality had yet to wear off, but there were signs of coming decay. Downtown department stores were losing ground in almost every large American city; within a couple of decades most of them would be gone. Petula Clark's favorite place had begun a process of decline that left many of the storied city centers moribund and largely vacant by the 1980s. Going there didn't cure anyone's depression; it made it worse.

Then, as we all know, something totally unexpected happened. Downtown made a comeback, fueled by restaurants, entertainment and eventually, in many cases, a robust residential population. The song turned out to be prophetic after all. It just took a few decades.

Why did the revival of city centers take place? And what will happen to them now, in the aftermath of the coronavirus shutdown? Those are questions worth thinking about seriously.

There is no one reason why downtowns came back. There are many reasons. The decline of violent crime ranks near the top of the list. In the 1990s it was widely predicted that a rising generation of super-predator criminals would terrorize central cities as never before. Nothing like that happened. Crime plummeted, and except for some dangerous hot spots in Chicago, Baltimore and a few other cities, it has stayed low. There were 2,245 murders in New York City in 1990. In 2018 there were 389. The rate of crime on the city's subways followed the same downward trajectory. Would-be urbanites perceived the changes surprisingly quickly and began moving back in, at first to open businesses, then to rent apartments and buy condos. Between 1980 and 2018, the residential population of central-city Chicago grew from 18,000 people to 110,000. Even downtown St. Louis increased its population by 71 percent.

The empty storefronts of the 1980s attracted artists, immigrants and other young pioneers, generating a boom in bars and restaurants that eventually lured in a more conventional population. In many ways, the downtown revival can be labeled a restaurant revival.

Those are tangible things. The most intriguing aspect of the downtown resurgence is a much more amorphous one: the desire of millennials for a lively urban experience that had eluded them in their suburban childhoods. Some of this was a function of entertainment options, but much of it was related to the re-emergence of physical proximity and walkable streets. It can be argued that the numbers here weren't really very large, compared to the number of young people who remained in the suburbs. But that's beside the point. The downtown comeback didn't take huge numbers. In a city of 500,000, a downtown cohort of 25,000 (5 percent) was in nearly every case enough to bring life to the downtown streets. For the most part, it wasn't public transit that attracted them; transit use in gentrified downtowns didn't increase all that much in the revival years. What these people wanted to do was walk — to work and to the places they went for fun.

THERE ARE OTHER REASONS why downtowns began thriving again, but let's stick to those three: declining crime, entertainment and a desire for physical proximity. How likely is it that they will survive the coronavirus shutdown?

Let's start with crime. That should be easy. Violent criminal offenses have come down substantially in virtually every big city in the past couple of months: During the peak virus weeks from mid-March to mid-April, they were down 33 percent in San Francisco, 25 percent in New York and nearly 25 percent in Los Angeles.

It's not hard to figure out why. There aren't many innocent visitors for criminals to prey on in the downtown streets these days. And even predators worry about getting sick in public places. Will there be a spike in street crime after the virus subsides? Maybe a small one. Crime was ticking up in New York and a few other places before the pandemic hit. But is there any reason to expect a return to the 1990s levels that sent middle-class urbanites fleeing to the suburban fringes? I can't think of one.

Entertainment is a more complicated case. There is no doubt that a significant percentage of the independently owned downtown bars and restaurants will fail as a result of the current crisis. This will be a genuine loss to urban society that shouldn't be minimized. But the restaurant scene will change in other ways as well. Outdoor dining has boomed in the past decade, even in parts of the country where you wouldn't necessarily expect it. But it could expand a great deal more. Driven by safety concerns, dining can leap from sidewalks and patios to entire downtown streets. European cities are trying this. Berkeley, Calif., has already turned most of its downtown streets into open-air dining centers. I hesitate to treat Berkeley as a typical American town, but going big outdoors may be the future of fine dining in quite a few American downtowns.

Perhaps more important, the empty storefronts that will plague many of these city centers will generate some silver linings of their own. As Derek Thompson pointed out in The Atlantic recently, commercial rents are likely to decline substantially. Bars and restaurants will be better able to afford them; soaring rents and onerous leases are the main reason locally owned restaurants had begun disappearing from downtown in alarming numbers even before the coronavirus struck. Somewhere down the line, it is reasonable to expect a revival of mom-and-pop storefront restaurants run by immigrant cooks and entrepreneurs who have an appealing and affordable product to provide. It will take a while, but it seems destined to happen.

That leaves the most challenging of the three factors: physical proximity. One of the first assumptions of the pandemic period was that urban density was making people sick. New York, after all, was the American capital of COVID-19. But more complete figures don't really support this idea: Virus cases have been more prevalent in the New York suburbs than in the city itself: 47 percent more in nearby Westchester County, for example. Moving from Manhattan to Westchester or to northern New Jersey is no way to avoid getting sick. One would have to move far beyond the city — 50 or 60 miles, or to a small town in a different part of the country altogether — and I question how many families will even consider doing that. Some, but not a critical number.

What remains is the most troublesome long-run prospect for downtown life: people working at home rather than commuting to central offices for their daily jobs. The media are full of stories about employees who have come to enjoy working at home and plan to do it even as the crisis fades. We have to take this seriously — but not without a dash of skepticism. Pundits have been predicting an Internet-fueled explosion of at-home workers and a decline of downtown offices ever since Frances Cairncross's book, The Death of Distance, forecast it in 1997. That book became a best-seller, but there was no death of distance. The best available figures suggest that in the closing years of the last decade, employment at home hadn't reached 5 percent of the overall American workforce.

Will that number take a jump in the coronavirus aftermath? Of course. People who never worked at home are discovering that they can do it without feeling isolated, and appreciate not having to endure the daily commute. Does that mean they will avoid downtown offices altogether? It's hard to imagine that. What seems more likely is that employees who came downtown five days a week will now be doing it more like two or three days a week, and offices will be used more for meetings and conferences than for day-to-day labor at the computer.

But the offices will still need to be there; some businesses may even need more space if their workers must sit six feet apart. The things that have drawn people to be part of workplace communities are not going to disappear, any more than they did when the Internet first allowed them to work remotely. A recent Brookings study of downtowns concluded that "while diseases will come and go, we can always retrofit our cities to make us feel safe while still delivering the proximity we crave."

That conclusion is right. We do crave proximity. We always have. It's one reason why so many millennials who spend much of their lives on phones and laptops have found the physical community of downtown streets so attractive in recent years. My bet is that this desire ultimately proves stronger than the virus, and stronger than the challenges the virus forces upon us.