Consonance and dissonance
Why some intervals sound stable and others ask for movement, and how music uses that tension.
Applied
Content under musical review. It may contain inaccuracies.
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Why some intervals sound stable and others ask for movement, and how music uses that tension.
Applied
A consonant interval sounds stable, at rest. A dissonant one sounds tense and seems to ask for something to move. It isn't about "nice" or "ugly": music needs both, the way a sentence needs pauses and questions.
A perfect fifth, open and stable:
A major third, consonant but more colourful:
A minor second, very tense:
And the tritone, unstable, as if hanging in the air:
The purest consonances match simple frequency ratios. The octave vibrates at 2:1, the fifth at 3:2 and the fourth at 4:3. The more complex the ratio, the more beating and roughness the ear hears:
| Type | Intervals |
|---|---|
| Perfect consonances | unison, octave, perfect fifth |
| Imperfect consonances | major and minor thirds and sixths |
| Special case | perfect fourth (consonant alone, dissonant above the bass in tonal style) |
| Dissonances | seconds, sevenths, the tritone and every augmented or diminished interval |
Play the open fifth string (A) and, at the same time, walk up the fourth string from fret 0 to 7. Each fret makes a different interval with the bass. Note which ones feel at rest and which push you toward the next note.
Train harmonic intervalsTonal music moves between tension and release:
Try holding one note while the chord changes underneath. A high E is consonant over C (the third), consonant over Am (the fifth) and dissonant over F (a major seventh), even though that dissonance sounds soft and modern. That's the principle behind tension notes.
Ear & improvisationTarget tonesImprovise over a backing track aiming at a specific tone of each chord.The line between consonance and dissonance isn't fixed. In the Middle Ages thirds were treated as imperfect or doubtful; in twentieth-century harmony sevenths and ninths work as stable colours. Persichetti suggests ranking intervals by degrees of tension rather than splitting them into two groups.
Timbre matters too: with distortion, the overtones of each note clash, and a major third can sound harsh while the fifth stays clean.