Aleatoric music is music in which either the composing process or its performance is determined at least in part by chance rather than predetermined by the composer. It is also referred to as indeterminate music or chance music. The term derives from the Latin word alea, which means "gambling" or "dice."
The chance element can be introduced in any of three ways. One is the use of random procedures to produce a determinate, fixed score. An example is the throwing of dice to determine the sequence of previously written measures and/or to determine which of two or more versions of each measure to use.
A second way is the providing of sections of music composed and notated in a conventional way but with their sequence determined by the performer(s) spontaneously during the performance.
A third, and the most indeterminate, is the replacement of some or all of conventional notation by other indicators, visual or verbal, to merely suggest how a work can be performed. For example, such indicators could be rectangles or other geometric forms to indicate relative pitches and to suggest rhythms.
Aleatoric music has a long history, dating back to at least the latter part of the 15th century, and there was a resurgence of interest from the early 20th century by composers of experimental art music. Moreover, aleatoric techniques have also become widely used in other art forms.