1 IDEAS     The École des Beaux-Arts in Paris, which dominated architectural education in the nineteenth and the early twentieth centuries, developed a strict method of teaching building design. After being assigned a problem, the student was isolated in a cubicle without the benefit of books or external advice, and given twelve hours to produce an esquisse , or preliminary design sketch. The chief purpose of this exercise was to decide on a parti , the governing idea that the student would turn into a detailed design over the next two months. A student handbook advised, "Selecting a parti for a problem is to take an attitude toward a solution in the hope that a building developed on the lines indicated by it will give the best solution of the problem." Although the esquisse is a thing of the past, the term parti has survived, for it embodies an enduring truth: great buildings are often the result of a single-and sometimes very simple-idea. When you enter the Pantheon in Rome, you take it all in at a single glance: a vast drum supporting a coffered dome, illuminated from above by an oculus, or circular aperture. Nothing could be simpler, yet no one would describe the Pantheon as a one-liner. Finished by Hadrian in the first century A.

D., it is one of the most influential buildings of Western architecture, having inspired Bramante at St. Peter's, Christopher Wren at St. Paul's, and Thomas Ustick Walter at the U.S. Capitol. King's College Chapel of Cambridge University, begun by Henry VI in 1446, is another building whose design expresses a singular idea: a tall space whose dematerialized walls are almost entirely stained glass. Modeled on a cathedral choir, the narrow chapel is eighty feet high and almost three hundred feet long.

There is no apse, no crossing, no rose window, just a numinous, soaring space. In buildings, the idea also informs the details. While the coffers of the Pantheon emphasize the solidity and weight of the dome and lead the eye up to the oculus, the lacy fan vaults of the Perpendicular Gothic chapel harmonize with the delicate tracery of the windows. A more recent example of a building whose design is driven by an idea is Frank Lloyd Wright's Solomon R. Guggenheim Museum in New York. Wright started with the insight that, given the high cost of Manhattan real estate, the museum had to be vertical. He explored four schemes, one of them octagonal, and settled on a spiral ramp coiling around a tall skylit space. The museumgoer would take the elevator to the top of the ramp, viewing the art as he descended.

Uncomplicated in conception, yet no matter how often I go there I am always surprised-and delighted-anew. Wright kept the details in the background: the spiraling balustrade, for example, is a plain concrete parapet with a rounded top; the ramp floor is simply painted concrete. "The eye encounters no abrupt change," he explained, "but is gently led and treated as if at the edge of a shore watching an unbreaking wave." Another modern museum that is based on a simple idea is the Sainsbury Centre for Visual Arts at the University of East Anglia in Norwich, a building designed by Norman Foster in the mid-1970s. Although the building was to house a variety of uses-exhibition spaces, a school of art history, a student cafeteria, and a faculty club-Foster accommodated them in what was basically an extremely long shed that recalls an elegant aircraft hangar. The long space, glazed at each end, does not feel tunnel-like, thanks to the daylight that filters down from skylights. The Sainsbury Centre has no architectural antecedents, it is as if Foster had asked himself: What if many different university functions were contained in one large space? CONCEPT HOUSES Ludwig Mies van der Rohe's house for Dr. Edith Farnsworth in Plano, Illinois, and Philip Johnson's own residence in New Canaan, Connecticut, are single spaces that ask an unusual question: What if all the walls of a house were glass? Both houses were designed as weekend retreats in the late 1940s; both are one-story boxes, the Farnsworth twenty-eight by seventy-seven feet, the Johnson thirty-two by fifty-six feet; and both are constructed of steel I-beams.

A transparent house should be as open as possible, and in both cases the interior is a column-free space divided only by freestanding elements containing closets, kitchen counters, bathrooms, and other necessities. There are no conventional rooms. Although Johnson finished his house first, he always credited Mies with the original idea.1 Johnson considered the German architect his model: "I have been called Mies van der Johnson," he once told Yale students; "it doesn't bother me in the slightest." But of his own house he said, "I won't say it's imitation Mies, because it's quite different." Johnson was not just being defensive-Mies's house sits in a floodplain and is elevated five feet in the air, which makes it appear to hover, while Johnson's house is planted firmly on the ground. And there are other differences. While Mies uses luxurious materials-travertine floors and tropical hardwood paneling-Johnson uses plain red brick.

The bathroom is a cylinder, "which would of course be anathema to Mies," said Johnson. Mies purposely designed the exterior of his glass house to be unsymmetrical-the roof and floor extend at one end to form a covered terrace-while Johnson made his four façades essentially identical, each with a door in the center. A final telling difference: Mies's steel is painted glossy white, the traditional color of garden pavilions, while Johnson's I-beams are matte black, making his house a machinelike presence in the natural landscape. The architect and writer Peter Blake observed that Johnson's house is European in conception, like a small classical palazzo, while the Farnsworth House is free, light, and airy in a way that makes it more American-despite that Mies had arrived in Chicago from Berlin only a decade earlier. Mies visited Johnson's glass house several times when they were working together on the Seagram Building. Johnson recounted that during his last visit, although Mies was supposed to stay overnight in the guesthouse, late in the evening he announced, "I'm not staying here tonight. Find me another place to stay." Johnson said that he didn't know what had set Mies off, whether it was a small disagreement that they had had earlier, or whether he simply didn't like the architecture.

Philip Johnson was an art collector and his house contained two freestanding works of art: Nicolas Poussin's landscape painting Burial of Phocion and a sculpture by Elie Nadelman. Mies, on the other hand, specified that no art was to be hung on the Primavera-paneled walls. My friend Martin Pawley spent a night in the Farnsworth House and recounted that the owner, Peter Palumbo, a London developer, respected the architect's wishes and hung paintings (I think they were by Paul Klee) only inside the bathroom. A sign asked guests to make sure to leave the bathroom door open after showering to avoid creating condensation that would damage the art. Martin described a memorable episode that occurred during his visit. The Fox River had overflowed its banks, as it did annually, and in the morning he was greeted by the sight of the butler bringing breakfast from the nearby main house (where Palumbo stayed) in a canoe. On that occasion, the terrace did double duty as a boat dock. Of the Farnsworth House, Mies's biographer Franz Schulze observed that it "is more nearly a temple than a dwelling, and it rewards aesthetic contemplation before it fulfills domestic necessity.

" That's a scholarly way of saying that a glass house is not very practical. Privacy was not the problem, since the Farnsworth House, like Johnson's home, is in the country, without close neighbors. Nor was the absence of separate rooms an issue, as both houses had only one occupant. The chief practical drawback of these glass houses was environmental: with unshaded plate glass and no air-conditioning, the interiors overheated in the summer, and were difficult to keep warm in the winter.2 Mies and Johnson made minimal provisions for ventilation: the Farnsworth House has two hopper windows at the bedroom end; the Johnson house has no openable windows at all, and is ventilated by opening one or more of the four doors. Since neither of the houses had insect screens, mosquitoes and flies were a problem, especially at night, when they were attracted by the light. In the 1920s, Mies had designed a residence in Czechoslovakia-the Tugendhat House-in which large sections of a glass wall were lowered into the floor to open the living room to the outdoors, without the benefit of insect screens. Are mosquitoes, moths, and flies a lesser nuisance in Europe than in America? Perhaps, for woven-wire insect screens are an American invention that came into widespread use in the second half of the nineteenth century when the screened porch became a domestic fixture.

The most elegant solution I have seen to accommodate insect screens in a modern house is in a Vero Beach, Florida, residence designed by Hugh Newell Jacobsen, in which windows and insect screens both slide out of sight into wall pockets, allowing the tall openings to be glazed, screened, or fully open. There is no place for wall pockets in a glass house. Of course, Mies and Johnson could easily have installed screens but they faced an aesthetic problem: metal screens app.