In music, heterophony is a type of texture created through the simultaneous variation of a melodic line. This can refer to a kind of complex monophony in which there is only one basic melody, but realized at the same time in multiple voices, each of which play the melody differently, either in a different rhythm or tempo, or with various embellishments and elaborations. The term (originally coined by Plato) was initially introduced into systematic musicology as a subcategory of polyphonic music, though is now regarded as a textural category in its own right.
Heterophony is often a characteristic feature of non-Western traditional musics - for example Japanese Gagaku, the gamelan music of Indonesia and the traditional music of Thailand. A remarkably vigorous European tradition of dissonant heterophony exists, however, in the form of Outer Hebridean Gaelic Psalmody.
Thai music is nonharmonic, melodic, or linear, and as is the case with all musics of this genre, its fundamental organization is horizontal... Thai music in its horizontal complex is made up of a main melody played simultaneously with variants of it which progress in relatively slower and faster rhythmic units... Individual lines of melody and variants sound in unison or octaves only at specific structural points, and the simultaneity of different pitches does not follow the Western system of organized chord progressions. Between the structural points where the pitches coincide (unison or octaves) each individual line follows the style idiomatic for the instrument playing it. The vertical complex at any given intermediary point follows no set progression; the linear adherence to style regulates. Thus several pitches that often create a highly complex simultaneous structure may occur at any point between the structural pitches. The music 'breathes' by contracting to one pitch, then expanding to a wide variety of pitches, then contracting again to another structural pitch, and so on throughout. Though these complexes of pitches between structural points may strike the Western listener as arbitrary and inconsequential, the individual lines are highly consequential and logical linearly. The pattern of pitches occurring at these structural points is the basis of the modal aspect of Thai music. (Morton 1978, p.21)
Heterophony is somewhat rare in Western Classical music prior to the twentieth century, but is frequently encountered in the music of early modernist composers such as Debussy and Stravinsky, who were directly influenced by non-Western (and largely heterophonic) music. Heterophony is a standard technique in the music of the post-war avant garde, however - for example Olivier Messiaen's Sept Haïkaï (1962), Pierre Boulez's Rituel: In Memoriam Bruno Maderna (1974-75) and Harrison Birtwistle's Pulse Shadows (1989-96). Benjamin Britten used it to great effect in many of his compositions, including parts of the War Requiem and especially his three Church Parables: Curlew River, The Burning Fiery Furnace and The Prodigal Son.