Tritone
The tritone spans six semitones with a just ratio of 45:32, a dissonance spelled as an augmented fourth or a diminished fifth.
From C
- Size
- 6 semitones
- Abbreviation
- TT
- Just ratio
- 45:32 (590.22 cents)
- Equal-tempered
- 600 cents (+9.78 from just)
- Inversion
- Tritone
What it sounds like
The tritone is a dissonance, and in tonal harmony it is the most unstable interval in common use. Its just ratio, 45:32, is complex, so the two notes clash and sound unresolved. Melodically it is awkward to sing, a leap of three whole tones that the ear wants to close. Harmonically it sits between the third and seventh of a dominant seventh chord, where it drives the pull toward the tonic. Equal temperament makes it exactly six semitones, half the octave, and its name refers to the three whole tones it spans.
How to recognise it by ear
The first two notes of 'Maria' from West Side Story form a tritone. Without that tune, use fa to ti in C, F up to B: the two notes sound unstable, and the pair seems to want to resolve to a neighbouring consonance. Sing both notes before playing them, since the pull is easier to feel in the voice. Practice: play F and then B, then move the B up a semitone to C, and listen for the tension releasing into a perfect fifth, F to C.
Theory
The tritone is its own inversion: an augmented fourth inverts to a diminished fifth, and both are six semitones. F to B is an augmented fourth, and B to F is a diminished fifth, so the spelling decides the name and the direction of resolution. A diminished triad, B D F, contains a diminished fifth, and the dominant seventh chord G B D F contains B to F. Its just ratio is 45:32, which measures 590.22 cents. The equal-tempered tritone is 600 cents, so the just size is 9.78 cents narrower.
The tritone above every note
Spelled by letter name, so the interval’s number is always right: a tritone above E♭ is not the same spelling as above D♯.
| From | To | Hear it |
|---|---|---|
On the piano
Further reading
- Tritone Substitution: The subV7 Chord That Still ResolvesHarmony · 6 min
- Seventh Chords and How They Resolve in Tonal HarmonyHarmony · 7 min
- Reading Intervals at Sight: Generic and SpecificFundamentals · 6 min
Questions
Why is it called the tritone?
The name means three whole tones. In equal temperament, six semitones equal three whole steps of two semitones each, and the interval from F to B spans F, G, A and B: three whole tones. The name describes the size of the interval, not its tuning, so it applies in both systems.
How do I tell an augmented fourth from a diminished fifth?
Count the letter names. F to B spans four letter names, F G A B, so it is an augmented fourth. B to F spans five, B C D E F, so it is a diminished fifth. The two sound identical on a keyboard, but the spelling shows which way the interval wants to resolve.
Why do tritones sound so tense in tonal music?
The ratio 45:32 is complex, so the partials of the two notes rarely line up, and the ear hears friction. In tonal music the tritone also points toward a specific resolution. In a dominant seventh chord, the tritone between the third and seventh pulls toward the tonic chord, which is why the dominant sounds unstable.