The career of avant-garde American composer John Cage holds a strange fascination. Musicians from all walks of life owe a debt to many of his ideas, even if the source often remains unacknowledged when those ideas are applied. And applied they have been, with increasing regularity in this post-Sgt. Pepper era - an era reverberating daily to the clatter of collapsing musical barriers.

But Cage was one of those 20th Century artistic pioneers whose goal-post-adjusting notions actually add up to more than the works themselves. Like Duchamp's urinal, the intrinsic, formal value of a given piece was less important than the gesture. For both artists, the shape thrown into relief was really the shape of things to come.

Take, for example, Cage's experiments with the 'prepared' piano from the late '30s. Metal or wood was placed inside the piano to alter the response from the strings and expand the timbres available to the keyboard player. In Cage's own words, the desire was "to place in the hands of a single pianist the equivalent of an entire percussion orchestra" - a sentiment that presages many of the concerns surrounding synthesizer development decades later.

Take also his exploration of 'found', or ambient sounds from the '40s onwards. Pieces such as Living Room (1940), Third Construction (1941), or Water Music (1952) feature doors banging, chairs knocking, wildlife sounds, pouring water or radio static - all constructed into thematic sound patterns as an alternative to conventional instruments. Even before the advent of sampling, we became quite used to bands such as Pink Floyd exploiting the surreal and emotive effects of noises of this kind, opening up the world to our ears and our ears to the world. The ultimate in ambience - total silence - was boldly declared by Cage in 1952 with a period of four minutes and fifty-three seconds of it, duly scored for piano (some 96 bars' rest), titled 4'33" and sparking a controversy that was to carve the composer a niche in artistic notoriety forever.

And what better pre-emption of the role of sequencers could there have been than Cage's use of carefully constructed backing tapes from the '50s, a technique directly employed by many musicians since. Probably the nearest thing to a 'cover version' of a John Cage number is the track 'Revolution #9' literally pieced together by George Martin and The Beatles for the 'White' album of 1968. This apparently random jumble of taped soundbites also draws on another of the composer's favourite muses: chance.

To give it its official title, 'aleatory' music basically just introduces opportunities for random departures, either by simply allowing for improvisation on the part of conductor or soloist, or by adopting more exotic methods during composition, such as dice-rolling, 'I Ching' throwing or even, as with Cage's 'Etudes Australes', laying constellation charts over a blank score to allow the heavens themselves to dictate the notes. 'Imaginary Landscapes', from 1951, consists of 12 radio sets whose frequencies are manipulated by 24 performers, a concept that neatly combines both ambient and aleatory factors in one fell swoop. It could be said that, in the search for ever more challenging techniques of composition and performance, Cage left few stones unturned. He certainly left nothing to chance.

Significantly, Cage's influence seems mostly to have been felt in the realms of pop. This may say something about the pretensions of those late '60s and early 70s 'pioneers' of progressive rock, but in the end, with so many of his techniques overtaken by developments in technology and taste, it actually serves to vindicate Cage's predilections with a force unlikely to be found in the 'serious' orbits from which he sprang. At any rate, hopefully time will finally demolish that most stubborn of barriers: the one between serious and popular music.