C#dim7 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 C#dim7 — drop 3 voicings
C#dim7 is C#, E, G and Bb — C#dim 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.
C#dim7 notes and formula
| C# | E | G | Bb |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭♭7 |
Leading-tone or passing chord — it can resolve almost anywhere.
Also written C#°7, C#o7 or C# diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play C#dim7
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.
C#dim7 has 10 of them, on strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 14th — every inversion the chord has: C# in the bass, E in the bass, G in the bass and Bb in the bass. The one to learn first is the Bb shape at the nut.
5 of them sit on strings 5-3-2-1, 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 xx2323 — no barre and down at the nut. None of the shapes for C#dim7 uses an open string, so every one of them is movable; the lowest sits at the 2nd fret. 2 of the 6 need a barre. Together they cover the neck from the 2nd fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| xx2323 | 2nd fret | E, 1st inversion | G | all fretted |
| x45353 | 3rd fret | C#, root position | G | all fretted |
| xx5656 | 5th fret | G, 2nd inversion | Bb | all fretted |
| 9x8989 | 8th fret | C#, root position | C# | barred |
| 9-10-11-9-11-9 | 9th fret | C#, root position | C# | barred |
| x-x-11-12-11-12 | 11th fret | C#, root position | E | 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 C#dim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (D#), the 11 (F#), the b13 (A) and the maj7 (B#).
How to use C#dim7
A diminished seventh divides the octave evenly, so C#dim7 has no single root and no single destination: it can lead to F# or to D, and it is the same four notes either way.
What to play over C#dim7
Every note of C#dim7 is in C# diminished and C# half-whole diminished.
Chords near C#dim7
Change one note of C#dim7 and you have C#dim (drop the sixth), C#m6 (the flat fifth becomes a fifth), C#m7b5 (the sixth becomes a flat seventh) or C#mMaj7b5 (the sixth becomes a major seventh).
C#dim7 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On C#dim7’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.