First formally developed in the early twentieth century, and popularized by Charles Ives, Henry Cowell, and John Cage, aleatory music is any music in which some component of composition (but not necessarily performance) is left to chance. It is a related music subgenre to indeterminate music, which refers to music in which the performance (but not necessarily the composition) is left somewhat up to chance.

The word "aleatory" or "aleatoric" is derived from Latin alea, meaning "dice." Dice, tarot cards, and other random number generators can be used to provide the numerical base upon which the features of a song are selected. Dice games have been used to decide the qualities of a piece of music, since at least the late fifteenth century, and Wolfgang Amadeus Mozart has been cited as having used these games to inspire musical variations during live performances at social events. John Cage used the I-Ching to develop of system of diagrams which informed his Music of Changes.

Generative music and algorithmic music are both related to the indeterminate and aleatoric music genres. Iannis Xenakis coined the term stochastic music to refer to music produced by random and algorithmic or generative processes such as Markov chains. Likewise, atonal music and twelve-tone music are part of the same prevailing phenomenon of early twentieth century music, of striving to step away from pre-contemporary conventions of tonality and modality, exploring the boundaries of what can be defined as musical sound versus noise.

Noise is often defined by musicians as random sounds not directed by deliberate human action, or occurring as a contingent audible effect of human actions intended for nonmusical purpose. Aleatory music investigates the question of how much randomness can be deliberately involved in a composition (or in a performance, as is the case with indeterminate music), before it ceases to sound musical to the ear, and devolves purely into noise.

Iron Noder 2015, 31/30

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