Chords
Diminished seventh chord
A diminished seventh chord (dim7) stacks three minor thirds: 1 ♭3 ♭5 ♭♭7, as in Bdim7 = B D F A♭. It is symmetrical and repeats every 3 frets.
What is a diminished seventh chord?
It is a diminished chord (1 ♭3 ♭5) with a diminished seventh (♭♭7) added on top, 9 semitones above the root, which sounds like a major sixth. Formula: 1 ♭3 ♭5 ♭♭7. Bdim7 = B D F A♭, C#dim7 = C# E G B♭, G#dim7 = G# B D F.
Symbols: dim7, °7, and in jazz often just °. Do not confuse it with the half-diminished chord (Bm7♭5 = B D F A), whose seventh is minor.
Why is the dim7 chord symmetrical?
Every note sits a minor third (3 semitones) from the next, and four minor thirds make exactly one octave (4 × 3 = 12). The result: Bdim7, Ddim7, Fdim7 and A♭dim7 contain the same notes. Any of the four can act as the root.
So there are only three different dim7 chords: Cdim7, C#dim7 and Ddim7. Every other name is one of these three spelled from another note. The chord also contains two tritones (B-F and D-A♭), which explains its strong tension.
How do you play a dim7 chord on guitar?
Shapes from the low E string to the high E string (x = string not played):
| Chord | Fingering | Notes |
|---|---|---|
| Ddim7 (open) | xx0101 | D G# B F |
| Cdim7 (5th string) | x3424x | C G♭ A E♭ |
| C#dim7 (5th string) | x4535x | C# G B♭ E |
| Gdim7 (6th string) | 3x232x | G E B♭ D♭ |
| G#dim7 (6th string) | 4x343x | G# F B D |
Thanks to the symmetry, each shape moves up 3 frets without changing the chord. Try it on strings 4 to 1: xx0101, xx3434, xx6767, then frets 9-10-9-10. It is always the same dim7, in four inversions. The chord identifier shows all four possible names for it.
What is the diminished seventh chord used for?
1. Dominant of harmonic minor. In A harmonic minor, the 7th degree gives G#dim7 (G# B D F), which is an E7♭9 without its root. Play Am x02210, Dm xx0231, G#dim7 4x343x, Am: the G# rises to A, the F falls to E.
2. Passing chord. C x32010, C#dim7 x4535x, Dm7 x5756x, G7 3x343x. The C#dim7 works as a rootless A7♭9, in other words a secondary dominant of Dm.
3. For improvising, the whole-half diminished scale (over Cdim7: C D E♭ F G♭ A♭ A B) contains all four notes of the chord.
Key takeaways
- Formula: 1 ♭3 ♭5 ♭♭7, three stacked minor thirds.
- Symmetrical: Bdim7 = Ddim7 = Fdim7 = A♭dim7, only three different dim7 chords.
- Every shape repeats every 3 frets (
xx0101,xx3434,xx6767). - Uses: vii°7 of harmonic minor, passing chord, rootless dominant.
Frequently asked questions
What is the difference between dim and dim7?
Dim is a triad (Bdim = B D F), dim7 adds a fourth note, the diminished seventh (Bdim7 = B D F A♭). In jazz, the symbol ° on its own usually means the full dim7.
Why can a dim7 chord lead to so many different chords?
Because each of its four notes can act as a leading tone, one dim7 can resolve to four different tonics. Bdim7 (B D F A♭) leads to C, Ddim7 to E♭, Fdim7 to G♭, A♭dim7 to A. That makes it a classic tool for modulation.
Why is it written A♭ and not G# in Bdim7?
Because the chord is built in thirds: B, D, F, and the next third up is some kind of A. It sounds identical to G#, but spelling it A♭ shows that it is a diminished seventh and not a sixth.
Related terms
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