Harlem is changing so quickly these days that you have only to visit it at monthly intervals to feel how swift the transformation has been. In a month, a building is razed and becomes an empty lot; an empty lot is filled with a steel frame; a steel frame is fleshed out into a building. Indeed, walking along Manhattan Avenue and Frederick Douglass Boulevard, a classically inclined pedestrian may well be reminded of Virgil’s description of the building of Carthage. The air resounds with the clamor of jackhammers, of men building, renovating, surveying. It is a hive of never-ceasing work.Turn your back, it seems, and everything is new.

To a degree unimaginable only a few years ago, gentrification is making itself comfortable throughout Harlem, especially in West Harlem around 118th Street. Nothing drives this home more than the gleaming new premises of some of New York’s most renowned realtors – Prudential Douglas Elliman, Corcoran, and Warburg. At the same time, however, these forces are converging to conserve, to re-create, or, where necessary, to invent an older Harlem, one that predates the arrival of large numbers of blacks in the neighborhood, and was built for and by wealthy whites like those who are now beginning to move in.

It is ironic that Harlem, which suffered more from bad Modernist planning and design than any other part of Manhattan, should now emerge as one of the largest beneficiaries of what is referred to as “contextual” housing. In practice that usually means something classical and, as such, something impossible without the tectonic shift in taste that took place 20 years ago.

Certainly you can find examples of contemporary Modernism in Harlem. The silvery boxes of the building that houses Nine West at 124th Street and Saint Nicholas Avenue, with their intermittently smooth and corrugated walls, are evocative reinterpretations of the machine aesthetic. Also good is the recently completed 314 W. 115th at the corner of Frederick Douglass Boulevard, a large volumetric mass whose flattened white and rose surfaces have turned to graphite gray.

But most of the work now being done in Harlem is vernacular, and here a paradox arises. Have we not all been told that the classical postmodernism of the 1980s is so thoroughly dead that no self-respecting architect designs that way anymore? Is it not evident, from all the design magazines, that we are witnessing a resurgent modernism whose unadorned angles and parsimonious curves are fashioned into gray and black monoliths?

That at least is the official story. But all over the country, the default mode of architecture is precisely the neoclassical architecture about which no one who counts has anything good to say these days. Once forged by architectural rebels, this style has now worked its way into the mainstream.

One especially powerful example of the style is the eight brownstone row houses and their imposing paired stoops on 118th Street between Manhattan Avenue and Frederick Douglass Boulevard.With the possible exception of the enlargement of the Jewish Museum a few years back, this is the only instance I know of a re-creation so successful as to seem thoroughly authentic to the period it imitates (in this case, the 1880s). For some time, I assumed that these structures – despite their pristineness – were more than 100 years old, until a local assured me that this site was a vacant lot only a few years back.

What is so impressive about this development is that, despite its contextualism, there is no easy historicism to it. The architecture does not slavishly imitate its models but enters into the logic of an earlier style and creates it anew. The architect has even achieved originality, applying to these spare, flattened facades, with their long, elegantly rectangular windows, the spirit, though not the letter, of that ultra-cool neo-Modernist vocabulary that is all the rage these days.

Far more typical of institutionalized neoclassicism, unfortunately, are the four row houses west of Frederick Douglass Boulevard at 120th Street. In these dull brick structures, with their rusticated base and oriel windows, you sense no personal input or initiative, only a clumsy amalgam of slightly ill-assorted parts. And like most neoclassical or contextual buildings, these houses’ great weakness, compared with the older architecture they imitate, is a feeling of ticky-tacky insufficiency.

You see this even more emphatically in much larger buildings like the Douglass at 279 W. 117th Street and 444 Manhattan Avenue at 118th Street. Both are huge and ungainly blocks of red and paler brick, with an assortment of fussy details that look so slight that a strong wind or a well-directed kick could topple them. They are not lovely, and their wrought-iron window grills are not fooling anyone into believing they are 100 years old. But for all their meretricious impurity, they are still better than the Modernist projects of 30 years back; with a little good will, we can allow ourselves to be gathered into their genteel illusions.

jgardner@nysun.com