B♭dim7 chord
B♭ diminished seventh. The diminished seventh chord: four notes stacked in equal minor thirds. It has only three distinct forms, and each one has four names.
Click a note to hear it
- Notes
- B♭ D♭ F♭ A♭♭
- Formula
- 1 ♭3 ♭5 ♭♭7
- Intervals
- P1 m3 d5 d7
- Also written
- B♭°7 · B♭o7
- Enharmonic
- A♯dim7
Notes in B♭dim7
B♭dim7 is spelled B♭ D♭ F♭ A♭♭: four notes stacked from the root B♭.
| Note | Interval above B♭ | Role | Formula |
|---|---|---|---|
| P1 | root | 1 | |
| m3 | third | ♭3 | |
| d5 | fifth | ♭5 | |
| d7 | seventh | ♭♭7 |
Inversions
Putting a different chord tone in the bass gives each inversion. The chord is the same; the bass note changes how it sounds and what it can lead to.
| Position | Notes, low to high | Symbol | Hear it |
|---|---|---|---|
| Root position | B♭ D♭ F♭ A♭♭ | B♭dim7 | |
| First inversion | D♭ F♭ A♭♭ B♭ | B♭dim7/D♭ | |
| Second inversion | F♭ A♭♭ B♭ D♭ | B♭dim7/F♭ | |
| Third inversion | A♭♭ B♭ D♭ F♭ | B♭dim7/A♭♭ |
On the piano
The root position voicing, with every chord tone lit in its own colour. Click a key to hear it.
On the guitar
B♭dim7 in standard tuning. The barre shapes below slide anywhere on the neck, so the same fingers give you every root. Strings run from the lowest (left) to the highest (right); X means do not play that string.
A-shape barre at fret 1
What it sounds like
Cdim7 is C, E♭, G♭ and B♭♭, which sounds as A, so the chord is a stack of three minor thirds, the same interval at each step. The four notes divide the octave evenly, so no note sounds more like a root than another. The chord holds two tritones, C with G♭ and E♭ with A, which make its tension extreme. The ear hears it as intensely unstable, and it pulls strongly toward a consonant chord. Its symmetry is the main source of its unusual, hard-to-place colour.
How it is used
In minor keys the fully diminished seventh is the leading-tone chord vii°7 of harmonic minor. In A minor it is G♯, B, D and F, and its root usually rises a semitone to the tonic, A. In major keys it is not diatonic, so it appears as a secondary or passing chord before a chord whose root is a semitone away. Romantic piano music and jazz both use it, often as a dominant substitute that can move in several directions.
How it is built
The diminished seventh is a root with a minor third, a diminished fifth and a diminished seventh, 0, 3, 6 and 9 semitones above the root. Common symbols are Cdim7 and C°7. Its seventh is written B♭♭, a double flat, which sounds as A, so the chord is spelled C, E♭, G♭ and B♭♭. Because the chord repeats every three semitones, only three distinct diminished seventh chords exist. Each one has four inversions with the same notes, so every note can serve as the root.
Which keys contain B♭dim7
B♭dim7 is not built from any one major or minor key’s own notes. It appears through borrowing, alteration or chromatic voice leading, which is part of why it sounds coloured.
Scales that fit B♭dim7
Scales that contain every note of the chord, so they can be played over it:
Other B♭ chords
- B♭
- B♭m
- B♭dim
- B♭aug
- B♭sus2
- B♭sus4
- B♭5
- B♭6
- B♭m6
- B♭7
- B♭maj7
- B♭m7
- B♭m7♭5
- B♭m(maj7)
- B♭7♯5
- B♭7sus4
- B♭add9
- B♭9
- B♭maj9
- B♭m9
- B♭7♭9
- B♭7♯9
- B♭13
How to practise it
Play the three distinct diminished seventh chords, rooted on C, C♯ and D, and hear that each set repeats. Then play Cdim7 and move every note up one semitone to reach C♯dim7, which is C♯, E, G and B♭. Listen to the whole chord shift by one step, and use that shift as a bridge between keys.
Further reading
- Seventh Chords and How They Resolve in Tonal HarmonyHarmony · 7 min
- Modulation: How a Key Change Is ConfirmedHarmony · 8 min
Questions
What notes are in a B♭dim7 chord?
B♭dim7 contains B♭, D♭, F♭, A♭♭. That is the root, third, fifth, seventh of the chord.
How do you spell B♭ diminished seventh?
Stack the intervals P1, m3, d5, d7 above B♭: B♭, D♭, F♭, A♭♭.
What other symbols mean B♭dim7?
Lead sheets also write it B♭°7, B♭o7. They are the same chord.
What is the difference between Cdim7 and Cm7♭5?
Both contain the diminished triad C, E♭ and G♭. Cdim7 adds a diminished seventh, which sounds as A, nine semitones above the root. Cm7♭5 adds a minor seventh, B♭, ten semitones above the root. The seventh is one semitone lower in the fully diminished chord, which makes it more symmetrical and more unstable.
Why are there only three diminished seventh chords?
The chord is built from minor thirds, so naming the root a minor third higher gives the same four pitches. C, E♭, G♭ and A repeat as E♭, G♭, A and C, and so on. The chords rooted on C, C♯ and D are the three distinct sets, and each one has four names.
How is the diminished seventh chord used?
It is used as a dominant-function chord in classical, Romantic and jazz harmony. Its symmetry lets it lead to several keys, since any of its four notes can be heard as a leading tone. Composers place it before a tonic, often on the leading tone of a minor key, to create strong tension that the tonic then answers.