Serialism is a term applied to the twentieth- century revolution in composition whereby traditional melodic, harmonic, rhythmic and tonal rules and conventions were replaced. Serial music is that in which a structural "series" of notes of notes governs the total development of the composition. It originated in Schoenberg's atonality, leading to his system of composing with 12 notes (1923). This system is based on use of a series of intervals )(note-row) involving in turn all 12 notes of the chromatic scale in any order selected by the composer. In its strictest application, no note should be repeated until the other 11 have appeared and the order of the series remains unaltered throughout the work, with certain permitted modifications. Schoenberg later broke his own rules and other modifications were introduced by Berg and Webern. While the series in Schoenbergs hands remained comparable with a theme, in Weberns it was more subtly pervasive and often not perceptible as a given sequence of 12 notes.
From the 1940's through 1950's, figures such as Messiaen, Boulez and Stockhausen were developing serialist techniques, and the arrival of electronic media in the 1960's greatly enlarged its scope. By the end of the 1960's, many composers renounced serialism as too restrictive, others, including Boulez, questioned its continued necessity because aleatory developments and new sounds available through electronic means achieve by synthesis the ends of serialism. Whatever the future of serialism, it remains a development which radically altered the tenets of musical composition.