Let's cut to the chase on the architectural merits of 10 Rittenhouse, the poshly proper apartment house that has lately assumed its place on Rittenhouse Square's northeast corner, as if the location were its birthright:

It's no Symphony House, not by an urban mile.

But, then, the 400-foot-tall, traditionally styled redbrick tower is not nearly as good as the diminutive, traditionally styled redbrick apartment house that it eyeballs directly across the square. Known as 250 S. 18th St., that early 20th-century high-rise is so unassuming, you've probably never bothered to look at it.

And therein lies the problem with 10 Rittenhouse, the latest offering from the office of New York architect Robert A.M. Stern. The luxury condo tower commits no cardinal sins against conventional taste, unlike its pink-rouged cousin on Broad Street. But neither does Stern's building make much of an effort to incorporate into its public face the craftsmanship that is the lifeblood of classical architecture.

The 33-story tower, which expects several units to sell for more than $15 million each, sports a facade so anorexically flat that it might be confused with a two-dimensional rendering. It's the ultimate social X-ray.

While the cream-colored, metal-trimmed bay windows provide a modicum of textural relief, they also look as if they were screwed into place at the last minute. What does it matter that the brand is the best that money can buy when nothing is done to weave the windows into the overall composition? If you want to see how real bays are done, take yourself over to 17th and Walnut Streets, and examine the routine 1920s office building on the corner.

An almost cynical absence of detailing has become the hallmark of Stern's Philadelphia work, a tally that includes the successful Comcast tower, the schematic McNeil Center for Early American Studies at 34th and Walnut Streets, and a strangely bipolar office design at the Navy Yard. Increasingly, I find that looking at a Stern building is like gazing into the eyes of someone who has undergone a lobotomy. There is an emptiness.

Stern, who moonlights as dean of Yale University's architecture school while overseeing a hugely successful design practice, has positioned himself as the Ralph Lauren of architecture. He may now be the profession's most prominent advocate for traditional styles.

There's nothing wrong with such architecture. This world has room for all tastes. But I'm not sure that Stern's large buildings are doing anything to further the traditionalists' cause. It's not enough for them to argue that bad classicism is better than bad modernism. Poor design knows no style.

It's often been said that Lauren's clothes enable their wearers to indulge fantasies about belonging to some polo-playing elite. In the same way, 10 Rittenhouse trots out just enough classical allusions to suggest it is the successor to the great prewar apartment houses. But the conceit is exposed by the proximity of the real thing.

The irony in all this is that the traditionalists claim the moral high ground by arguing that their buildings reflect their specific context. Stern says that 10 Rittenhouse was inspired by Philadelphia's Federal-style townhouses, yet the generic result feels no less placeless than a modernist glass tower. The design is a weak variation on Stern's Chatham, built nearly a decade ago on Manhattan's upper east side, down to its heavily marbled oval lobby.

For all these disappointments, there are a great many things that 10 Rittenhouse does right. The project went through a contentious zoning hearing, and four townhouses were sacrificed on 18th Street to make room for the tower. Stern's design pays back the city with great sensitivity at the ground level.

Not only is the garage hidden underground, it avoids the usual cavernous and unattractive entrance ramp by utilizing an elevator. The developers, Robert Ambrosi and Hal Wheeler, of ARC Wheeler, had the ground floor wrapped with retail spaces, and have found excellent tenants. It helps that the 18th Street shop windows are large and crisply designed.

The developers also restored the gorgeous facade of Walnut Street's beaux-arts Rittenhouse Club, a yearlong labor that cost close to $1 million. That building, together with the handsome Allison Building next door, forms the base in a classical sense for 10 Rittenhouse's shaft, and some of that beauty rubs off.

The tower's facade may want for detailing, but at least the brick is the real deal, even if the veneer on the panels is a mere half-inch thick. After a while, the mortar joints separating the square panels no longer matter.

Stern's office saved its real skill for the apartments, designed with Ismael Leyva. With their generous hallways, foyers and laundry rooms, the condos - the salespeople prefer to call them "homes" - really do match prewar standards. And the bay windows that look so awkward on the outside provide residents with fabulous views and staggering amounts of light. The experience, incidentally, is not unlike being inside a contemporary tower.

Stern's design isn't the first on Rittenhouse Square to fall short of what that great public park deserves. The square is now entirely ringed by high-rises, one for virtually every decade of the last century. Most of the clunkers are modern designs, it's true. But the postwar Dorchester and 220 W. Rittenhouse Square are looking pretty good, especially in comparison with 10 Rittenhouse.

And that raises the question: If Philadelphia could build the sexy, modern Dorchester in 1964, why can't it build its equivalent today? Why have wealthy Philadelphians lost faith in modern design, and the optimistic future it still promises, to the extent that they prefer a traditionalist pretender?

Stern's other recent homage to the great prewar apartment houses, Manhattan's 15 Central Park West, is far more convincing because the craftsmanship is better. Those condos, however, sell for double and triple the prices of 10 Rittenhouse, located on the most desirable piece of real estate in Philadelphia.

The economics of construction make it hard enough to create a decent modern building in Philadelphia, never mind a credible, well-crafted traditional one. When the real estate market comes back, it will be worth asking ourselves if there is a better way.

Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com.