Parallel fourths
Parallel fourths arise when two voices move at the same time in the same direction a perfect fourth apart. Older harmony teaching judges them unfavourable in sound, above all against the bass. In early organum, by contrast, they were the building principle, and in the music of the 20th century they are a deliberate sound.
- Distance
- perfect fourth (5 semitones)
- Early organum
- building principle, parallel fourths and fifths
- Harmony teaching
- against the bass judged unfavourable in sound
- Today
- tone colour in jazz and modern music
The same motion a fourth apart
The perfect fourth has a frequency ratio of 4:3 and counts as a perfect consonance, which however is treated like a dissonance above the bass. Two voices running in parallel a fourth apart therefore sound peculiar: empty and archaic, at the same time less resolved than parallel octaves. Older harmony teaching judges them unfavourable in sound.
Parallel fourths on the white keys
Two voices a fourth apart, rising by step. The first three fourths are perfect. The fourth, F–B (marked), is augmented: on the white keys alone parallel fourths stay perfect only up to E–A.
All fourths perfect, with B♭ instead of B
With the B♭ the fourth fourth too is perfect (F–B♭, five semitones). The sound stays empty and hard; the voices hardly fuse, but they do not seem properly separate either.
In the glossary: Parallel octaves · Quartal harmony · Interval inversion
A question of period
| Period | Treatment of parallel fourths |
|---|---|
| 9th–11th century | organum: parallel fourths and fifths as the principle of writing |
| Harmony teaching (counterpoint, figured bass) | the fourth above the bass counts as a dissonance, parallels are avoided |
| 20th century | chords in fourths and parallel fourths as a means of sound |
In early polyphonic singing, organum, fourths and fifths were the framework of the writing. The voices ran in parallel a fourth or fifth apart. With the development of harmony teaching the judgement changed. The distinction between consonance and dissonance led to the fourth above the bass being treated as dissonant and its parallels being avoided. In the 20th century they reappeared as a deliberate means of sound.
Why the fourth works differently
The fourth is the inversion of the fifth. Both complete each other to the octave. That is why it shares some properties of the fifth. Unlike parallel fifths, however, parallel fourths between upper voices are not forbidden in harmony teaching: they occur in chains of six-three chords, see Parallel motion. Only the fourth to the bass is delicate. In a purely diatonic sequence the size of the fourth changes: between the white keys F and B lies an augmented fourth. Led in parallel on the white keys the fourths are therefore not all perfect.
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Related terms
Parallel octavesQuartal harmonyParallel seventhsTetrachordInterval inversionPerfect intervalsUnison
Editor: Maik Krohm · reviewed on 3 October 2026
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