Aleatoric music stands against totally ordered serialism by introducing controlled chance. Its radical pole is John Cage, who composed scores using the I Ching and wrote the conceptual piece 4′33″ of complete silence, in which the random sounds of the hall become the music.
A moderate, “controlled” version was developed by Witold Lutosławski: within precisely written episodes, players perform their parts unsynchronised, creating a shimmering sound mass. Aleatoric music gave the 20th century the notion of open form — a work that sounds different each time.
