Cdim7 guitar chord
The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped.
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About Cdim7 — drop 3 voicings
Cdim7 is C, Eb, Gb and A — Cdim with a diminished seventh stacked on top.
It sounds suspenseful and rootless. Three stacked minor thirds divide the octave evenly, so the same four notes spell four dim7 chords and the shape repeats every three frets.
Cdim7 notes and formula
| C | Eb | Gb | A |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭♭7 |
Leading-tone or passing chord — it can resolve almost anywhere.
Also written C°7, Co7 or C diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Cdim7
The same operation one voice further down: the third voice from the top falls an octave and becomes the bass.
That leaves a bigger hole under the top three notes, so a string gets skipped: the muted string in the middle is the shape, not a mistake.
Cdim7 has 9 of them, on strings 6-4-3-2 and strings 5-3-2-1, from open position up to the 13th — every inversion the chord has: C in the bass, Eb in the bass, Gb in the bass and Bbb in the bass. The one to learn first is the Gb shape at the nut.
5 of them sit on strings 6-4-3-2, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Start with xx1212 — no barre and down at the nut. None of the shapes for Cdim7 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 2 of the 7 need a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| xx1212 | 1st fret | Eb, 1st inversion | Gb | all fretted |
| x34242 | 2nd fret | C, root position | Gb | all fretted |
| xx4545 | 4th fret | Gb, 2nd inversion | A | all fretted |
| 8x7878 | 7th fret | C, root position | C | barred |
| 8-9-10-8-10-8 | 8th fret | C, root position | C | barred |
| x-x-10-11-10-11 | 10th fret | C, root position | Eb | all fretted |
| x-x-13-14-13-14 | 13th fret | Eb, 1st inversion | Gb | all fretted |
The same notes rebuilt from scratch give 5 shell, 14 drop 2 and 1 open string voicings, each on its own page.
Tensions. A shell of Cdim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (D), the 11 (F), the b13 (Ab) and the maj7 (B).
How to use Cdim7
A diminished seventh divides the octave evenly, so Cdim7 has no single root and no single destination: it can lead to F or to Db, and it is the same four notes either way.
What to play over Cdim7
Every note of Cdim7 is in C diminished and C half-whole diminished.
Chords near Cdim7
Change one note of Cdim7 and you have Cdim (drop the sixth), Cm6 (the flat fifth becomes a fifth), Cm7b5 (the sixth becomes a flat seventh) or CmMaj7b5 (the sixth becomes a major seventh).
Cdim7 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Cdim7’s sound and use this page follows Stefan Kostka, Dorothy Payne & Byron Almén, Tonal Harmony (McGraw-Hill, 8th ed., 2018). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.