Aleatoric Music

Aleatoric music involves the use of chance in either the composition or performance of the piece. John Cage became a strong proponent of aleatoric techniques, even going so far as to use them in lectures as well as musical compositions. To be clear, the Sonatas and Interludes are not aleatoric works, so the John Cage piece on our playlist does not incorporate aleatoric elements. However, John Cage is so associated with chance music that it would seem odd not to study this important 20th century technique in connection with Cage.


Aleatoric music (also aleatory music or chance music; from the Latin word alea, meaning “dice”) is music in which some element of the composition is left to chance, and/or some primary element of a composed work’s realization is left to the determination of its performer(s). The term is most often associated with procedures in which the chance element involves a relatively limited number of possibilities.

Types of Indeterminate Music

Some writers do not make a distinction between aleatory, chance, and indeterminancy in music, and use the terms interchangeably. From this point of view, indeterminate or chance music can be divided into three groups: (1) the use of random procedures to produce a determinate, fixed score, (2) mobile form, and (3) indeterminate notation, including graphic notation and texts.

The first group includes scores in which the chance element is involved only in the process of composition, so that every parameter is fixed before their performance. In John Cage’sMusic of Changes (1951), for example, the composer selected duration, tempo, and dynamics by using the I Ching, an ancient Chinese book which prescribes methods for arriving at random numbers. Because this work is absolutely fixed from performance to performance, Cage regarded it as an entirely determinate work made using chance procedures. On the level of detail, Iannis Xenakis used probability theories to define some microscopic aspects of Pithoprakta (1955–56), which is Greek for “actions by means of probability.” This work contains four sections, characterized by textural and timbral attributes, such as glissandi and pizzicati. At the macroscopic level, the sections are designed and controlled by the composer while the single components of sound are controlled by mathematical theories.