C Diminished Seventh Chord (Cdim7)

1Composition: what it contains

C – E♭ – G♭ – B𝄫

Symbol

Cdim7

Also written

Cdim7, C°7, Co7

Formula

1 ♭3 ♭5 ♭♭7

2Appearance: diagrams and sound

On the guitar

On the ukulele

On the piano

On the staff

On bass and as an arpeggio

3Indications: what it is used for

The vii°7 chord of harmonic minor, resolving to i (or to I in major as a borrowed chord). It acts like a V7♭9 without its root, so it is a dominant substitute. It is widely used as a passing chord between diatonic chords (I–♯I°7–ii, IV–♯IV°7–I/5), in classical music, ragtime, gospel, gypsy jazz and film scores. Because it divides the octave into four equal minor thirds, any of its four notes can be the root, and it can resolve to four different keys.

4Dosage: how to practise it

On guitar, learn one four-string shape and move it up three frets: it is the same chord in a new inversion. On piano, play it in all inversions and notice the identical spacing. Practise resolutions from vii°7 to i in minor keys, letting each voice move by step, at 60–90 BPM. Practise the passing progression I–♯I°7–ii7–V7. There are only three distinct dim7 chords; learn all three in five minutes a day.

5Warnings and common mistakes

Do not confuse dim7 with m7♭5: the seventh here is diminished (enharmonic to a major sixth). Many charts write just 'dim' or '°' for this four-note chord; check the context. Correct spelling uses stacked minor thirds with a double flat on the seventh, which can look strange but matters for reading. Overuse quickly sounds melodramatic. On guitar, avoid letting open strings ring that do not belong.

6Interactions with chords, scales and keys

Inversions

• Inversion 1 · Cdim7/E♭ · E♭ – G♭ – B𝄫 – C Play
• Inversion 2 · Cdim7/G♭ · G♭ – B𝄫 – C – E♭ Play
• Inversion 3 · Cdim7/B𝄫 · B𝄫 – C – E♭ – G♭ Play

Scales to play over Cdim7

• C Half-Whole Diminished Scale
• C Whole-Half Diminished Scale

7Other presentations available

The same chord from every note

C♯dim7 Ddim7 E♭dim7 Edim7 Fdim7 F♯dim7 Gdim7 A♭dim7 Adim7 B♭dim7 Bdim7

Other chords on C

C Cm Cdim Caug Csus2 Csus4 C5 C6 Cm6 C7 Cmaj7 Cm7 Cm7♭5 Cm(maj7) C7sus4 Cadd9 Cm(add9) C6/9 C9 Cmaj9 Cm9 C11 Cm11 C13 C7♭9 C7♯9 C7♯5 C7♭5