One weakness of modernist architecture that was not recognized at first was the question of the addition. For the great buildings of the past this was not a problem. Organized along a lattice of monumental axes, they could simply thrust those axes farther into space, and grow. Both the Louvre and the Metropolitan Museum of Art grew in this manner, and transformed themselves from compact blocks into leviathans with no loss of legibility or coherence. Strangely enough, modern architecture—for all its celebration of the free plan—is not so free, at least not in this respect. The free plan might indeed be polished to a kind of crystalline perfection, as in Mies van der Rohe’s Barcelona Pavilion, but the moment one tries to add to it, and alter the invisible calculus of its equilibrium, the building falls apart. If one extends the axes of movement, it becomes a pinwheel; if one multiplies them, it becomes a labyrinth. Things are no better on the exterior. To the extent that a modernist building is also a work of abstract sculpture, then every addition is a disfigurement—or so recent controversy over proposed additions to Louis Kahn’s Kimbell Museum and Marcel Breuer’s Whitney Museum has shown.

Strangely, the museum most intimately associated with the course of modern architecture, the Museum of Modern Art in New York, has never been embarrassed by additions. MOMAitself, after all, is nothing but a loose congeries of additions, huddling companionably around its sculpture garden. It has never