The Selected Letters of John Cage edited by Laura Kuhn Wesleyan University Press, 651 pp., $40.00

There are certain creative figures whose mature works are almost tangential to their enduring artistic influence. Marcel Duchamp falls into this group, as does Andy Warhol. And so, certainly, does John Cage (1912–1992). He opened doors—floodgates, really—and dissolved definitions; if most of his own compositions now seem less interesting than the ramifications of his ideas, there can be little doubt that his oceanic spirit changed the topography.

It is fitting, perhaps, that the son of a Los Angeles inventor should have attracted initial public attention with his own homemade instrument—the “prepared piano,” a standard-issue piano transfigured with the help of nut bolts, screws, erasers, rubber bands, and other material placed between its strings. Described so dryly, the idea calls to mind some sort of Dada stunt (“C’mon kids, let’s see what we can squeeze into this piano!”), but the resulting sound was specific, exotic, and euphonious, a percussion orchestra in a box.

A 1943 concert at the Museum of Modern Art made Cage famous—and controversial. “About forty kinds of instruments were employed, ranging from thunder sheets and a ‘string piano’ to cowbells, flower pots and even an audio-frequency generator,” Noel Straus reported in The New York Times. “But practically all the ‘music’ produced by the various combinations of them had an inescapable resemblance to the meaningless sounds made by children amusing themselves by banging on tin pans and other resonant kitchen utensils.”

Other listeners were there to cheer, of course, and the resulting debate, once launched, would continue for almost half a century. Today, the very early Cage pieces (mostly for percussion, piano, or prepared piano as well as an almost medieval-sounding string quartet) seem fanciful and engaging. But they are his only pieces that are still played with any regularity in the concert hall because, after the early 1950s, Cage became drawn to exploring new concepts of music, rather than the traditional compositional disciplines of arranging specific pitches, rhythms, and sounds into an exact and convincing artistic statement.

And so he changed course and continued to change for the rest of his life. Imaginary Landscape No. 4 (1951) was written for twelve radios and two performers, one manipulating the frequency knobs while the other played with the volume controls. Although the notation was precise, the resulting sounds necessarily varied from performance to performance, as most of their substance came from what was on the air at any given time.

Atlas Eclipticalis (1961) was a compilation of eighty-six instrumental parts that were created by tracing astronomical charts onto scored music paper, to be played in whole or part by any ensemble, chamber or orchestra. HPSCHD (1969; created with Lejaran Hiller) included parts for seven amplified harpsichords, mostly playing a tangle of Mozart, and fifty-two computer-generated tapes.

Stimulating as these compositions may be to…