Every other week or so, another unfortunate New Yorker is killed or injured as bits of masonry fall from the sky, and another badly-maintained skyscraper starts to crumble. From time to time, a section of one of the great Manhattan avenues subsides and cars tumble into the abyss. Now and then, as you wait for a subway train which will take you under one of the rivers that split the city, your eye is caught by a notice telling you not to be alarmed if the air becomes thick with dust. It's only asbestos being removed from the tunnel.
The odd time, too, you witness a human collapse as someone explodes with rage or frustration. A wild-eyed man catches your eye on the train and starts to rant about the Emperor of Abyssinia. You pass an immigration office, see a crowd has gathered, and learn that a Russian man, unable to cope with New York and unable to get anyone to listen to his request to be sent home, has thrown himself from a 20th floor window. Your eye is caught by a tabloid headline announcing that terrorists are planning to release nerve gas in the subways. The asbestos suddenly seems friendly.
If any of these things happens and you are a New Yorker, you stop for half a second, give an inward shrug and move on. Something else is sure to happen soon. Any moment now, the vast kaleidoscope will take another turn, and some new, equally strange event will come into view. The thought that hovers over the city - that this crazy place cannot last much longer - is, for the billionth time, temporarily banished. New York seems impermanent because it scarcely belongs to anything so fixed as a nation or a state. Perched offshore, with only the grim fastness of The Bronx overflowing on to the mainland, the city is not quite in the United States. It is a weird, unnatural archipelago, rising from the fresh waters of the Hudson River and the salt waters of New York Bay, its scattered parts joined by ferries, tunnels and bridges. The stars and stripes fly over it, and American law holds sway, but it is really a global city, washed by wave after wave of migrants and refugees, adventurers and chancers.
The constant motion makes the place seem at once monumental and temporary. On the one hand, the city is continually torn down and rebuilt. The pace of change is such that New Yorkers get nostalgic for things that have only just disappeared, and that, when they were there, were actually despised. Times Square, for instance. A few years ago, the thing to say about Times Square was that it was a dirty disgrace, a sleazy slum and, at night, a war-zone. Now it has been cleaned up. Beautiful, turn-of-the century theatres such as the magnificent New Amsterdam have been lovingly restored. The junkies and hookers, the strip-joints and peep shows have been moved out. But now the thing to say, with as much snootiness as you can muster, is that Times Square has been "Disneyfied". People get misty-eyed for a place already transformed in the memory from a sordid, dangerous dump to a sexy, deliciously dangerous merry-go-round.
And yet, along with this frantic reinvention, there is also an extraordinarily conservative side to New York. In some respects, the texture of its everyday life is remarkably old-fashioned. It is full of the small shops and services that most modern cities have lost. There are chain stores such as The Gap and supermarkets like Gristede's and Food Emporium. But there are also, at street level, medieval food carts, cheap little diners, shoe repair shops, newsagents, greengrocers, bars, barber shops, antique stores, pet shops, delis, pharmacies and tobacconists.
They create what John Updike has called the "startling, steamy, rain-splotched intimacy of the side-streets" of New York. They also give the city a feeling of being a patchwork of times as well as peoples. The eye is drawn back and forth, from a monumental post-modern skyscraper to a little, 19th-century cubby-hole in which an immigrant family from God knows where is filling a tiny niche in the vast marketplace of the city.
And it is, after all, the immigrants who make the city. Since 1982, about 1.7 million new immigrants - as much as the entire populations of Dublin and Belfast put together - have settled in New York. If you move around the city now, there's an easy way to spot which part of the globe you've wandered into. Discount phone centres, offering cheap phone calls to specific international locations, have mushroomed. On Roosevelt Avenue in Queens, you can call Peru, Colombia and Ecuador at special rates. Off the Eastern Parkway in Brooklyn, West Indians call the Caribbean. To the east, along Utica Avenue, Haitians, Egyptians and Nigerians queue for the phones. Between the two airports, La Guardia and JFK, most of the calls are in Chinese.
In northern Manhattan, a new French Harlem has arisen, where Guineans, Ivorians, Malians and Senegalese phone home. Even on Staten Island, the most conservative and insular of the five boroughs, there is now a Liberian enclave, started by refugees from a terrible civil war. If you have breakfast in a diner, it will probably be served and cooked by Mexicans. If you want your jacket dry cleaned, you usually hand it over to a Korean. If you buy a paper at a street kiosk, you will expect to get it from a Gujarati Indian or a Pakistani. If you order a car to go the airport, you are likely to encounter an especially odd example of the enforced co-existence that is the essence of New York. So many of the car companies are owned by Israelis that if you forget who to call, you only have to think of a place in the Holy Land - Haifa, Tel Aviv, Jaffa, Carmel, Sinai - and call directory inquiries. But, when the car arrives, the driver will almost certainly be a Middle Eastern Muslim - a Jordanian, a Syrian, even an Iraqi.
No one in New York could ever mistake all this manic variety for a Utopia of equality and harmony. No one can miss the cruelty and indifference that are often the other side of the city's freedom and opportunity. Yet there is nowhere else that has survived in relative peace for a century while containing such a vast array of human differences. New York's equilibrium may be maintained only by frantic movement. Its more fortunate inhabitants may achieve serenity only by shutting out the human disasters that litter the streets. But the city itself flows on, as hopeful and despairing, as full of diversity and of similarity, as the world that feeds it.