Hold onto your seats -- the New York Guggenheim had motorcycles, now the San Francisco Museum of Modern Art has chairs. Organized by Aaron Betsky, "Sitting on the Edge" features more than 100 chairs (plus tables, a clock, some flatware and other objects) collected by San Franciscans Michael and Gabrielle Boyd.

The items on view range from a 1903 side chair by Peter Behrens to work made during the 1980s. All are modern or, as the exhibition subtitle has it, ''Modernist." Michael Boyd characterizes the collection by noting that "each object is a minimal expression of some sort." That's not minimal in the sense of Minimal art (although four furniture designs by Minimalist sculptor Donald Judd are included), but minimal in the general sense of "paring down…to only meaningful elements -- the minimum needed to capture and sustain interest." Eliminated therefore are the efforts of the Postmodernists and latter-day ornamentalists. No neo-Biedermeier from Michael Graves, no bookproof bookcases from the Memphis group.

Also required for inclusion in the collection, of course, is that the object has the minimum structure needed to support the human bottom. These are not "art" chairs, with a look-don't-touch attitude, such as some of Shiro Kuramata's chair-shaped objects seen at the S.F. MOMA in the fall of '97. The Boyd chairs are all designed to be sat in.

The exhibition also investigates the ergonomics of chairs -- a term not yet invented when most of the pieces were being designed. Each work is viewed in relation to the human body, and how it may or may not promote comfort and health. Dr. Galen Cranz examines many from the Boyd collection, modern classics by Aalto, Breuer, Mies van der Rohe, the Eameses and others in her new book The Chair: Rethinking Culture, Body, and Design (1998,W.W. Norton) and finds almost all of them ergonomic disasters. She gives passing marks to only two both of them on view here: Le Corbusier's 1928 Chaise-lounge Basculant and Rietveld's 1918 stiff-as-a-board Red/Blue Chair. Who knew? She claims that the Neo-Plasticist masterpiece supports the head and gives "the rib cage and pelvic bowl an opportunity to open out."

Although designed for use, the chairs are necessarily displayed on platforms that preclude our opening our pelvic bowls in public. As a wall-mounted note by Betsky explains, the platforms also prompt us to see them as artistic rather than utilitarian objects. But, of course, we see them as artistic objects shaped by utility. For this reason, the chairs express not only the respect for function but also the earnest work ethic and utopian goals of Modernism -- and perhaps do so more clearly than most of the fine art of the same period.

The exhibition is accompanied by an excellent catalogue with several essays and over 100 full-page color images, priced at $24.95 (paper) and $40 (hardcover).