Diminished fifth
The diminished fifth is a fifth reduced by a semitone, so six semitones instead of seven. It sounds like the tritone and counts as one of the most unstable intervals. You meet it in the diminished triad, the dominant seventh chord and the blue note.
- Size
- 6 semitones, three whole tones
- From the fifth
- perfect fifth (7 semitones) minus a semitone
- Sound
- tense, restless, demands resolution
- Sounds the same
- augmented fourth, tritone
- Example
- B–F
Six semitones
The page Interval Ear Training explains how intervals are named: you count the number of staff steps spanned. A qualifier is added: perfect for unison, fourth, fifth and octave, major or minor for second, third, sixth and seventh. Diminished and augmented are added when a note is altered chromatically. The diminished fifth is therefore a fifth whose upper note lies a semitone lower than the perfect fifth requires.
Perfect fifth: B to F♯
Five degrees counted from B, seven semitones: a perfect fifth. It sounds open and stable.
Diminished fifth: B to F
Also five degrees, but only six semitones: the F instead of F♯ makes the fifth a semitone smaller. It sounds tense and undecided. The two semitone steps B–C and E–F lie exactly at the ends.
On the piano every interval corresponds to a fixed number of semitone steps. The exercise page names the series: tritone six, perfect fifth seven. So does the diminished fifth sound the same as a tritone? On the piano yes, because both have six semitones. The name depends on how the interval is written: as a fifth (B–F) or as a fourth (F–B).
The tritone: undecided
The page Intervals describes the tritone as three whole tones on top of each other and calls it the notorious “diabolus in musica”. Medieval theorists considered it impure because of its tense, unstable sound and avoided it in sacred music. It divides the octave symmetrically into two equal halves, its ratio in equal temperament is the square root of two. On the guitar the tritone lies six frets apart.
Because it has no simple frequency ratio, according to the article Why the fifth sounds hollow it sounds floating and undecided: there is no common period of the two vibrations.
Where the diminished fifth occurs
- In the diminished triad: On the page Chords it says: diminished means two minor thirds (3 + 3 semitones), tense and restless, with a diminished fifth, for instance C–E♭–G♭. On the page Identify Chords it is explained how to tell it from minor: both have a minor third, the difference lies in the fifth. Minor has a perfect one, diminished a reduced one. Listen to the top note.
- On the seventh degree: The page Diatonic chords explains the small circle sign at vii°: a diminished triad, tense and restless, which mostly presses to the tonic. In C major that is B–D–F.
- In the dominant seventh chord: In G7 (G–B–D–F) the major third B and the minor seventh F form a tritone. The article The leading tone describes the resolution: B pulls a semitone up to C, F a semitone down to E.
- In the blues scale: The article The pentatonic as a first improvisation describes what happens if you add the diminished fifth to the minor pentatonic, in A minor the E♭: the blues scale arises. This added note is called the blue note, it is never held but passed through. It is the one deliberately placed friction in an otherwise frictionless system.
| Triad | Thirds | Fifth | Effect |
|---|---|---|---|
| Major | major + minor | perfect (7 semitones) | bright, stable |
| Minor | minor + major | perfect (7 semitones) | dark, stable |
| Diminished | minor + minor | diminished (6 semitones) | tense, restless |
| Augmented | major + major | augmented (8 semitones) | floating, hard to place |
Hearing the resolution
The diminished triad on B consists of B, D and F. It usually resolves to C major, because B wants to go to C and F to E. Listen:
Common mistakes
- Confusing diminished and perfect fifth: Both have five degrees. The diminished has six semitones, the perfect seven.
- Confusing minor and diminished: Both triads have a minor third. Only the fifth distinguishes them.
- Holding the blue note: It is never held, but passed through.
Continue on Maikstrings
Related terms
TritoneDiminished triadAugmented fourthDominant seventh chordBlue NotePerfect fifthIntervalBlues scaleDissonance
Editor: Maik Krohm · reviewed on 3 October 2026
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