Parallel Motion
Two voices moving the same way at a fixed interval — watch the fifths and octaves
Related
Parallel motion has two voices moving in the same direction while keeping the same interval. Parallel thirds and sixths are common and thicken the harmony; parallel fifths and octaves are avoided in traditional counterpoint because the two parts stop sounding independent and become one line doubled.
Its difference from similar motion: similar looks only at direction, parallel also requires the interval to stay. The usual mistake is to treat parallel fifths and octaves as absolutely forbidden — in planing, Impressionism and pop arranging they are legitimate colour; the rule depends on style, not physics.
Read deeper → voice leading
Sources
- 平行五度/八度的限制与例外，参 The New Grove Dictionary of Music and Musicians, "Voice leading" 与 "Parallel fifths"；本文为原创表述
Used for fact-checking only; all prose is original.