SCIENTIFIC dictionaries define Brownian motion as the random movement of microscopic particles in a liquid or gas.
In the unfolding lexicon of modern dance, the term has come to denote a similarly unpredictable phenomenon: the choreography of Trisha Brown.
A founder of the Judson Dance Theater in the early 1960s - with choreographer Merce Cunningham, composer John Cage, and painter Robert Rauschenberg - Brown has traversed rooftops, walls, and lakes in pursuit of new ways of moving and performing.
What she found, and brought back to the stage, is a pageant of jarring collisions and chance encounters, thwarted expectations and subtle ironies, off-balance steps, and weighted gestures.
President Clinton nominated her to the National Council on the Arts in March, and on June 19 she will receive the $25,000 Samuel H. Scripps American Dance Festival Award for lifetime achievement. Her previous honors include a $325,000 ``genius'' grant from the MacArthur Foundation in 1991.
``Trisha is one of the few choreographers who, after reducing the art of dance during the 1960s, has been able to build it up again and put flesh around the bones,'' says Charles Reinhart, director of the American Dance Festival. ``She has originated new ways of moving and new ways of putting together dances.''
Brown's latest work, ``If you couldn't see me,'' exemplifies her commitment to charting new ground. Throughout the 10-minute solo, which premiered last week at New York's Joyce Theater and features a costume and score by Rauschenberg, she never faces the audience.
``It's astonishingly difficult, physically, because all of my communicative and expressive systems are on the front side of my body,'' she said over tea in her SoHo loft a week before the premiere. ``I didn't know what was on the back side, nor did I know how to combine gestures in a form that would be of interest. You can't just shake your hips.''
At times Brown's legs seem to unhinge themselves, exploring the air like vines. Her arms spread like cantilevers bearing unseen weights, or float with unknown purpose.
Her muscular back, exposed by the plunging line of a flowing white costume, ripples with momentum and energy. By allowing audiences to witness the workings of the back, the engine that drives a dancer's body, she and Rauschenberg infuse ``If you couldn't see me'' with a characteristic touch of irony.
Like much of her choreographic work, the dance evolved through a compositional technique Brown calls ``problem solving.'' She imposes a restriction on herself and relies on her imagination, intelligence, and wit to find a solution.
The premise of facing away from the audience not only sparked choreographic innovation, Brown says, but also mitigated the inherent narcissism of performing alone. ``If you couldn't see me'' is her first solo in 15 years.
Brown says she has found an unfailing source of theatrical energy in her lasting embrace of the ironic, the unconventional, and the unpredictable. ``Defying expectations is a dialogue I have with my audience,'' she says. ``Are you paying attention? I don't want to repeat what I know.''
Some of the most fascinating things that occur in her studio, and therefore on her stage, are errors, she says. Mistakes. ``The magnificent awkwardness that sometimes occurs when a dancer crosses her wires,'' she explains, ``is more beautiful than anything I could make.''
Modern dance, like poetry, derives much of its allure from an artist's ability to expand the vocabulary of movement. Few choreographers have proven themselves capable of turning new phrases and inventing new forms with such fluency and agility as Brown. She and her company move like subatomic particles, their motion governed by forces less predictable than gravity.
* The Trisha Brown Company will dance at Jacob's Pillow in Lee, Mass., from June 14-18. Upcoming appearances also include Macky Auditorium in Boulder, Colo., for the Colorado Dance Festival (July 16-30); and the Dance Aspen Festival Theater in Aspen, Colo. (Aug. 2-6). Brown will also perform her new solo June 19 at the American Dance Festival, in Durham, N.C., when she receives the Scripps ADF Award.