New Yorkers who love the Upper West Side can get a little spooked by how much Jane Jacobs disliked it. After all, doesn’t the West Side have the stretches of old buildings she so admired usefully recycled for new and different purposes? And isn’t it endowed with wide sidewalks and mixtures of street uses, especially on the commercial corridors?

Well, she designated it one of her “areas of city failure.” She even called Morningside Heights “a surly kind of slum.”

The West Side functioned as one of her many urban labs. Indeed, she developed her famous principle about the necessity of short blocks from the overly long blocks of West 86th Street, the location of her family dentist. So mundane did she consider the neighborhood that she dreaded the visits, even when they were topped off by a side trip to the Hayden Planetarium on 81st Street.

To many West Siders, West 86th Street is a great boulevard, akin to a residential Champs-Elysées. To Jacobs, it was a dreary stretch of dull residential buildings divided by four lanes of cars.

In the famous Chapter 9 of her “The Death & Life of Great American Cities,” titled “The Need for Small Blocks,” she singled out 86th Street between Columbus Avenue and Central Park West as the paradigm of the self-isolating street. Because much of the West Side is on a grid, rigid and unyielding compared to her beloved Greenwich Village, she categorized the dozens of streets parallel to 86th Street as “stagnant, long, backwater blocks.” She said someone living on the long blocks of 86th Street would have no reason for entering adjacent blocks such as 87th or 89th. Instead, a “mutual isolation of path” inevitably develops, keeping people apart.

A City Council member who represents the West Side, Gale Brewer, sniffs at this characterization, pointing out that West Siders are among the most gregarious of New Yorkers. “This neighborhood is never sterile,” she says. “We have more people out on the streets and benches of some of these blocks than live in most cities.”

Although Columbus Avenue has for much of its history been a retail street, Jacobs called it “an abrupt garish gash” amid the “Great Blight of Dullness.” Perhaps, but a real estate broker for Brown Harris Stevens, Julie Maxey-Allison, who has lived on 86th Street for more than 30 years, says the West Side is now the most sought-after part of the city, especially for families with children. “All the kids stuff is here,” Ms. Maxey-Allison says. “This has become the suburban area of New York because this neighborhood has the parks, Central and Riverside, which is what keeps people uptown.”

Apartments that sold 20 years ago for $35,000 now command $3 million, she notes. Condominiums, a form that barely existed in New York 20 years ago, routinely sell for “$4, $5, $6 million, all cash, even though you can borrow 90%,” she says. The Europeans and Israelis in particular love the West Side.

But does the West Side’s current economic success mean Jacobs was wrong or her analysis flawed? One must remember what it was like back then, Ms. Maxey-Allison says. “People went to 87th Street, bought the brownstones cheap, and fixed them up. But they were scared,” she says, talking about one of the streets Jacobs explicitly criticized.

Violent crime was high, breakins and muggings were common, street people were aggressive. The state and city governments dumped troubled people, including former felons and drug users, into welfare hotels on side streets. The West Side was not only a mess, it was a dangerous mess.

“Then 275 W. 96th St. happened, and it changed everything,” Ms. Maxey-Allison says, referring to the huge yellow Zeckendorf building, called the Columbia, which runs the length of the west side of Broadway between 96th and 97th streets. Opened in 1983, its importance lay in pushing the boundary northward for ordinary New Yorkers. “The apartment buildings between 86th and 96th streets are simply beautiful,” she says. “There’s nothing wrong with them, but nobody went up there in the old days. Suddenly the boundary moved north of 96th Street, and buyers realized all the great space that was available. Especially families that had been cramping their children into maids’ rooms on the Upper East Side, looked at the barns on the Upper West Side and realized this space is just better.”

Or as activist Aaron Biller, president of Neighborhood in the Nineties, argues,”.Still, whenitopened, the Columbia was an outpost.”

Condos in that outpost now sell for a great deal of money, though may remain a bargain compared with buildings farther south. A Corcoran senior vice president, Samantha Reiss, calls the $2.19 million price tag on a four-bedroom, three-bath, 1,800-squarefoot condo with balcony and full city view “a great value.”

Ms. Maxey-Allison calls the apartment a combo — combined from two distinct units — that will require first board approval and then time and money to make it work. Otherwise, it’s being offered at “not too bad a price,” she says. The Columbia profits from the kind of public transportation Jacobs thought was essential. It sits on the 96th Street West Side IRT subway stop, benefits from frequent 96th Street crosstown buses, and, for car owners, has a direct shot to the West Side Highway.

Would Jacobs have regarded the building as yet another “massive anti-city project” or as a neighborhood asset? It has made some attempts to conform to her principles by providing ground-floor retail on most of its streetscape — but the retail remains pretty dull by her standards. Nor is the Columbia really connected to the rest of the neighborhood, Mr. Biller says, noting that it is self-contained, with its own health club and Olympic-size swimming pool. Certainly it is not an example of the “mending that is all but invisible” that Ms. Jacobs thought was appropriate for new buildings in old urban neighborhoods. But in planting the flag, its presence encouraged new development and rehabilitation all around it — development that ironically now offers it serious competition.

Ms. Maxey-Allison points out that the West Side has many more condos being built, and that many buyers prefer the newest buildings — except when compared to pre-war buildings or those with absolutely perfect locations, neither of which really applies to the Columbia.

Yet the shrewdly named Columbia performs another Jacobs function — it links disparate neighborhoods, acting as a self-designated southern border to Columbia University’s academic community. “Zeckendorf started a trend that connected the affluent areas of Columbia University, which came down at that point very tentatively to 110th Street and only very spotty below that, to the rest of the West Side,” Mr. Biller says.

A Columbia University professor of urban affairs, Ester Fuchs, who moved to Morningside Heights in 1980, says she thinks Jacobs was just plain wrong in much of her assessment of the West Side. “This neighborhood was always beautiful, but it was caught in a decline caused by forces way beyond the city’s control — cheap mortgages encouraging the middle class to leave, for one. If Columbia University hadn’t intervened early to buy up property and stabilize the market, things would have been far worse.” She adds, however: “We did have serious crime, and the safety issue trumps everything else. Now we’re benefiting from years and years of low crime rates. But look how long it took for people to accept that crime was really down.”