About Adim — triad voicings
Adim is A, C and Eb — Am 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.
Adim notes and formula
| A | C | Eb |
|---|---|---|
| 1 | ♭3 | ♭5 |
Unstable — it does not sit still.
Also written A°, Ao or A diminished. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Adim
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.
Adim has 47 of them, on the low-middle three, the high-middle three, the middle four strings, the top three strings, the bottom four strings, the bottom three strings, the top four strings, strings 6-4-3-2 and strings 5-3-2-1, from open position up to the 13th — every inversion the chord has: A in the bass, C in the bass and Eb in the bass. The one to learn first is the C shape at the nut, which is the easiest grip here.
6 of them sit on the middle 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 x0121x — 1 open string and only 3 fretted notes. 1 of the 5 shapes here sits in open position. None of them needs a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x0121x | open position | A, root position | C | 1 open string |
| 53x54x | 3rd fret | A, root position | Eb | all fretted |
| xx78x8 | 7th fret | A, root position | C | all fretted |
| x-12-10-x-10-11 | 10th fret | A, root position | Eb | all fretted |
| x-12-13-14-13-x | 12th fret | A, root position | C | all fretted |
Tensions. A shell of Adim, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (D) and the b13 (F).
How to use Adim
In which keys. Every note of Adim belongs to G minor (the ii°, the supertonic) and Bb major (the vii°, the leading tone).
What to play over Adim
Every note of Adim is in A blues, A locrian, A altered, A diminished and A half-whole diminished.
Chords near Adim
Change one note of Adim and you have Am (the flat fifth becomes a fifth), Adim7 (add the sixth), Am7b5 (add the flat seventh), AmMaj7b5 (add the major seventh), Am/C (the flat fifth becomes a fifth) or Am/E (the flat fifth becomes a fifth).
Adim is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Adim’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.