The earliest significant use of music
indeterminacy features is found in many of the compositions of American composer
Charles Ives in the early 20th century.
Henry Cowell adopted Ives’s ideas during the 1930s, in such works as the
Mosaic Quartet (String Quartet No. 3, 1934), which allows the players to arrange the fragments of music in a number of different possible sequences. Cowell also used specially devised notations to introduce variability into the performance of a work, sometimes instructing the performers to improvise a short passage or play
ad libitum. John Cage is regarded as a pioneer of indeterminacy in music. Beginning in the early 1950s, came to refer to the (mostly American) movement which grew up around Cage. This group included the other members of the so-called
New York School:
Earle Brown,
Morton Feldman and
Christian Wolff. Others working in this way included the
Scratch Orchestra in the United Kingdom (1968 until the early 1970s) and the Japanese composer
Toshi Ichiyanagi (born 1933). In Europe, following the introduction of the expression "aleatory music" by Meyer-Eppler, the French composer Pierre Boulez was largely responsible for popularizing the term (Boulez 1957).