About Gdim — triad voicings
Gdim is G, Bb and Db — Gm with the fifth lowered as well.
It sounds compressed and unstable in every direction. Rarely a destination; it is where a line passes through on the way somewhere.
Gdim notes and formula
| G | Bb | Db |
|---|---|---|
| 1 | ♭3 | ♭5 |
Unstable — it does not sit still.
Also written G°, Go or G diminished. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Gdim
Three notes on one string set. No seventh, so nothing is claimed about the chord beyond its quality.
Thin on their own, excellent over a bass line or against someone else’s harmony.
Gdim has 48 of them, on the top three strings, the low-middle three, the bottom four strings, the bottom three strings, the high-middle three, the top four strings, the middle four strings, strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 14th — every inversion the chord has: G in the bass, Bb in the bass and Db in the bass. The one to learn first is the Bb shape at the 2nd fret, which is the easiest grip here.
6 of them sit on the bottom four strings, 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 xx56x6 — only 3 fretted notes and low, at the 5th fret. None of the shapes for Gdim uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 15th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 31x32x | 1st fret | G, root position | Db | all fretted |
| xx56x6 | 5th fret | G, root position | Bb | all fretted |
| x-10-8-x-8-9 | 8th fret | G, root position | Db | all fretted |
| x-10-11-12-11-x | 10th fret | G, root position | Bb | all fretted |
| 15-13-x-15-14-x | 13th fret | G, root position | Db | all fretted |
Tensions. A shell of Gdim, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (C) and the b13 (Eb).
How to use Gdim
In which keys. Every note of Gdim belongs to F minor (the ii°, the supertonic) and Ab major (the vii°, the leading tone).
What to play over Gdim
Every note of Gdim is in G blues, G locrian, G altered, G diminished and G half-whole diminished.
Chords near Gdim
Change one note of Gdim and you have Gm (the flat fifth becomes a fifth), Gdim7 (add the sixth), Gm7b5 (add the flat seventh) or GmMaj7b5 (add the major seventh).
Gdim is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Gdim’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.