Parallel sevenths

What it means

Parallel sevenths occur when two voices of a polyphonic texture move together in the same direction while maintaining a constant interval of a seventh throughout.

Since the seventh is a dissonant interval, such parallel motion stands out particularly in classical tonal writing and was generally regarded as an error in traditional part-writing theory.

Musical use

Unlike parallel fifths or octaves, whose avoidance is mainly justified by the resulting loss of independence between the voices, parallel sevenths are additionally troubling because the ongoing dissonance is never resolved in the conventional sense but persists as continuous tension without progression.

In freer, especially impressionist or jazz-harmonic music, parallel sevenths are by contrast used deliberately as a coloristic device, for instance when entire chord blocks, sevenths included, are moved in parallel beneath a melody to create a modern, 'floating' sound quality.

Parallel sevenths should be distinguished from parallel fifths and octaves, the classic basic cases of forbidden parallel motion, and from the mere use of individual seventh chords, in which the seventh is not carried through in parallel motion but used within a single chord.

Performance practice

In polyphonic writing, listen deliberately for whether two voices move in parallel at a constant interval of a seventh over several notes, so you can consciously recognize this effect. If you use parallel sevenths compositionally, deploy them deliberately for a particular coloristic effect rather than letting them arise unintentionally.