About Fdim — triad voicings
Fdim is F, Ab and Cb — Fm 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.
Fdim notes and formula
| F | Ab | Cb |
|---|---|---|
| 1 | ♭3 | ♭5 |
Unstable — it does not sit still.
Also written F°, Fo or F diminished. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Fdim
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.
Fdim has 48 of them, on the high-middle three, the top three strings, the low-middle three, the top four strings, the bottom four strings, the middle four strings, the bottom three strings, strings 6-4-3-2 and strings 5-3-2-1, from open position up to the 13th — every inversion the chord has: F in the bass, Ab in the bass and Cb in the bass. The one to learn first is the F shape at the nut, which is the easiest grip here.
6 of them sit on the top 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 xx34x4 — only 3 fretted notes and low, at the 3rd fret. None of the shapes for Fdim uses an open string, so every one of them is movable; the lowest sits at the 3rd fret. None of them needs a barre. Together they cover the neck from the 3rd fret to the 13th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| xx34x4 | 3rd fret | F, root position | Ab | all fretted |
| x86x67 | 6th fret | F, root position | Cb | all fretted |
| x-8-9-10-9-x | 8th fret | F, root position | Ab | all fretted |
| 13-11-x-13-12-x | 11th fret | F, root position | Cb | all fretted |
Tensions. A shell of Fdim, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (Bb) and the b13 (Db).
How to use Fdim
In which keys. Every note of Fdim belongs to Eb minor (the ii°, the supertonic) and F# major (the vii°, the leading tone).
What to play over Fdim
Every note of Fdim is in F blues, F locrian, F altered, F diminished and F half-whole diminished.
Chords near Fdim
Change one note of Fdim and you have Fm (the flat fifth becomes a fifth), Fdim7 (add the sixth), Fm7b5 (add the flat seventh), FmMaj7b5 (add the major seventh) or Fm/C (the flat fifth becomes a fifth).
Fdim is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Fdim’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.