Avant-garde composer John Cage wrote hundreds of pieces of music, many of them controversial, but none more so than 4'33' - a work in three movements, all of them silent. Although normally played - or not played - by a pianist, it can be performed by any combination of instruments, the only essential one being a stopwatch.
Cage first publicly discussed the concept of silent music in flippant terms in a 1947 lecture in which he announced that he intended to 'compose a piece of uninterrupted silence and sell it to Muzak Co. It will be three or four and a half minutes long - those being the standard lengths of canned music - and its title will be Silent Prayer.'
The idea was not wholly original. Fifty years before Cage's lecture, French humourist Alphonse Allais published the sheet music for a silent composition called Funeral March for the Obsequies of a Deaf Man - a work very much in the spirit of the blank sheet of paper he exhibited at the Galerie Vivienne in 1883 entitled First Communion of Anaemic Young Girls in the Snow.
Czech composer and pianist Erwin Schulhoff also beat Cage to the punch in 1919 with a silent composition entitled In Futurum, in which complicated silent rhythms are meticulously notated.
Cage wasn't alone in believing that music that didn't exist could be sold in the same way as music that did. It has been asserted that the reason he formalised his 1947 Silent Prayer concept as the 1952 4'33' concert work was that he had heard 'silent' records were to be placed in jukeboxes to offer those prepared to pay a short respite from music they disliked.
However, his achievement was to persuade concert audiences to sit still for just over four and a half minutes and listen to nothing but ambient sound. Cage's point was that for those who could hear, there was no such thing as silence, and that any combination of sounds could constitute music - an idea derived from his studies of Zen Buddhism and the I Ching.
Not all audiences have played along. When pianist David Tudor gave the piece its first performance at Woodstock on August 29, 1952, many of those attending muttered mutinously through the three short movements, and some walked out.
Cage was undismayed. 'What they thought was silence, because they didn't know how to listen, was full of accidental sounds. You could hear the wind stirring outside during the first movement. During the second, raindrops began pattering on the roof, and during the third the people themselves made all kinds of interesting sounds as they talked or walked out,' he later recalled.
Today, performances of the piece are usually received, if not in literal silence, at least with a reverential hush. People know what to expect.
Cage, who died in 1992, continued to experiment with silence in his works, one of which, entitled As Slow as Possible, is being played on a church organ in Germany in a performance scheduled to last 639 years.
The concert, which can be heard at www.john-cage.halberstadt.de, began, appropriately, with a 17-month rest before the first note was played, and chords change at intervals of months or years. The rest is silence.