You probably would claim to know a modern building when you see one. Yet there are unquestionably many different modern styles. What, then, makes a modern building modern if there is no stylistic uniformity? What are modernism's diversities?

During the last decade or so, critics of modern architecture have tended to treat modernism in design as if it were a singular style. And the particular style often cited to illustrate the failure of modern design is that inspired by the work and polemics of Mies Van der Rohe, the ultimate modern, "corporate box" architect.

What latter-day critics, and presumbly much of the public, found lacking in many modern buildings were traditional architectural conventions, motifs and symbols. Having stripped away classical ornament, modern designers allegedly neglected to invent acceptable substitutes for these historic, culturally based elements. Tom Wolfe's "From Bauhaus to Our House" asserts that modern architects condemned such elements as bourgeois.

Compare Mies' Martin Luther King Memorial Library at 9th and G streets NW, a black steel and glass package built in 1972, with the Beau Arts Renaissance revival library at 8th and K streets NW, designed by Ackerman and Ross at the beginning of the century. Is there any doubt as to which would be considered visually the richest and most meaningful by today's historicist standards?

But further looking reveals that such simplistic, polarizing, black/white contrasts are misleading. The purity and potential sterility of orthodox Bauhaus and international-style design were not blindly embraced by all post-World War II architects, despite their having studied under the European masters.

Other branches of modernism sprouted as many architects abandoned the exclusive strictures of the Bauhaus in search of new iconography. Tom Wolfe labeled some of these renegades "apostates," and they included such unlikely bedfellows as Eero Saarinen, Edward Durell Stone, Louis Kahn, I. M. Pei and even old Bauhauser Marcel Breuer.

One alternative to the minimalist, slick buildings cleanly enveloped in glass, metal or smooth masonry was to design buildings that "broke the box." They derived their primary expressive imagery from manipulation of building mass, volumetric complexity and surface texture or relief.

Their architects took many design cues from Le Corbusier's extraordinary work in which he harmoniously combined seemingly abstract, three-dimensional geometric composition with two-dimensional, almost classical proportioning and systematization.

Whole buildings, as well as building facades, offered dynamic sculptural opportunities for the play of solid against void, of light against shade. The chosen material for structure and finishes often was concrete. Notable advocates -- among them Yale's Paul Rudolph and Harvard's Jose Luis Sert -- believed that modern buildings should be shaped to show on the exterior specific internal functions, spaces and service networks.

Such expressional architects likely would prefer the Arena Stage, designed by Harry Weese in 1960, or John Johnsen's 1960s Mechanic Theatre in Baltimore, over the Kennedy Center, which discloses nothing of its contents. Or they might have admired John Carl Warnecke's brutalistic library building (1970) on the campus of Georgetown University or Pei's softer, sand-colored Christian Science church (1972) at 16th and I streets NW.

Maybe other heroic, boldly expressive D.C. buildings would have been found appealing: the FBI Building (1975, after 10 years of construction) on Pennsylvania Avenue by Chicago's C. F. Murphy Associates; the Forrestal complex (1970) on Independence Avenue by Curtis and Davis; Marcel Breuer's HUD Building on 7th Street SW (1968) and Hubert Humphrey Building for Health and Human Services (1978) at Independence Avenue and 3rd Street SW, and L'Enfant Plaza (1970), designed by Pei and Vlastimil Koubek.

During this same era, another kind of Washington modernism evolved, exemplified by the Kennedy Center, completed in 1969. Designed by Stone, it is clearly a modern building smoothy packaged. But this slightly decorated, massive white marble box ringed by slender gold columns alludes in its vaguely classical way to a Greek temple or perhaps the Lincoln Memorial.

Next door is the enigmatic Watergate complex, designed by Italian architect Luigi Moretti in 1965. Its neo-Baroque forms, stop-and-start balconies and appended details disguise somewhat its massiveness and ribboned horizontality. Someone has said that "the Watergate Apartments are a wedding cake, and the Kennedy Center is the box it came in."

In 1964, Stone's new building for the National Geographic Society was completed at 17th and M streets NW. It had a lid-like top, a colonnaded base and a skin of mullions and vertical-strip windows running from base to lid.

In Southwest D.C. a few years later, Stone's Nassif Building, housing the Department of Transportation, appeared like an inflated version of its predecessor. Had Stone found a formula for being modern and traditional at the same time? He used it again at Prince George's Plaza and the Georgetown University Law Center.

The Museum of American History (formerly History and Technology) opened in 1964, the first new Mall building since Pope's 1941 National Gallery. The successor firm to McKim, Mead and White designed this blockbuster sheathed in pink marble, aspiring to relate its ornament-free mass to the Federal Triangle across Constitution Avenue. The Air and Space Museum, designed in the early 1970s by Hellmuth, Obata and Kassabaum, exhibits similar gestures.

While white boxes and concrete crates were being built, still another brand of modernism appeared in Washington. More humane and pluralistic in detailing, material and color, these buildings typically made use of brick as well as concrete, metal, glass, wood and other materials. They generally displayed more scale-giving elements on their facades: railings, balconies, screens and trim.

Examples include buildings by Keyes, Lethbridge and Condon such as Columbia Plaza (1962) between Virginia Avenue and E Street NW, and Tiber Island (1965) in redeveloped Southwest. The German Chancery (1964) on Reservoir Road northwest of Georgetown was designed by Egon Eiermann and is a particularly good example of a large but finely scaled, decorated modern building.

Then there was Saarinen, a stylistic chameleon capable of out-Miesing Mies, as he did in his high-tech General Motors Technical Center in Michigan, while indulging in metaphoric romanticism with his bird-like TWA terminal at Kennedy Airport and his unprecedented, wing-like Dulles Airport. Conceived in the 1950s, Dulles remains one of the capital area's most memorable and admired structures.