Half-Diminished Seventh Chord
A half-diminished seventh chord combines a diminished triad with a minor seventh. Cm7 flat 5 contains C, E flat, G flat and B flat. It appears diatonically as vii in major and as ii in natural minor, where tonal harmony often sends it to V and i.
- 1-flat 3-flat 5-flat 7
- diminished triad
- minor seventh
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Which notes are in Cm7 flat 5?
Use the formula 1-flat 3-flat 5-flat 7:
- C: root
- E flat: minor third
- G flat: diminished fifth
- B flat: minor seventh
Symbols include Cm7 flat 5 and the half-diminished symbol, a slashed circle followed by 7.
Why is it called half-diminished?
The bottom triad C-E flat-G flat is diminished.
The seventh C-B flat is minor, not diminished. A fully diminished seventh chord lowers B flat to B double flat.
Half describes the combination of diminished triad and minor seventh; it does not mean that only half the notes are altered.
How do you build it from Cm7?
Cm7 is C-E flat-G-B flat.
Lower G to G flat. The root, minor third and minor seventh remain fixed.
This one-semitone change introduces the tritone C-G flat.
Where does it occur in a major key?
The half-diminished seventh occurs on degree vii.
In D-flat major, degree 7 is C. Stacking C-E flat-G flat-B flat gives Cm7 flat 5.
As vii, it commonly leads toward the tonic D flat through C-D flat and G-flat-F motion.
Where does it occur in minor?
Natural minor produces a half-diminished chord on degree ii.
In C minor, degree ii is D. D-F-A flat-C forms Dm7 flat 5.
Tonal minor often follows it with G7 and Cm: ii half-diminished-V7-i.
How does the minor ii-V-i resolve?
In Dm7 flat 5-G7-Cm:
- D can remain as the fifth of G7, then move to E flat or C.
- F remains the seventh of G7, then falls to E flat.
- A flat can fall to G.
- C can fall to B, the leading tone in G7, then rise to C.
Voicings choose which of these lines are present. Practice each voice separately.
What is the difference from Cdim7?
Cm7 flat 5 is C-E flat-G flat-B flat.
Cdim7 lowers the seventh to B double flat, sounding as A on an equal-tempered piano.
The fully diminished chord stacks equal minor thirds and is symmetrical. The half-diminished chord has a major third from G flat to B flat and keeps a clearer root.
What is the difference from Cm7?
Cm7 uses G natural. Cm7 flat 5 uses G flat.
Cm7 contains a perfect fifth and no tritone from root to fifth. Lowering the fifth changes the chord symbol and common function.
Compare both over a C bass so the root remains unambiguous.
Which scales fit it?
C Locrian matches Cm7 flat 5 and adds D flat, F and A flat.
C Locrian natural 2 uses D natural and comes from melodic minor. Jazz players often use it when the natural 9 fits the melody and progression.
The chord symbol alone does not specify which second to use. Check the key and surrounding voices.
How do inversions work?
There are four bass positions: C, E flat, G flat and B flat.
The chord retains its pitch classes, while inversion changes bass direction and spacing.
In ensemble writing, keep the tritone and seventh clear. The root may be supplied by bass.
How should you practice it?
Build Cm7, then lower G to G flat. Next lower B flat to B double flat for Cdim7.
Play Dm7 flat 5-G7-Cm in several voicings. Sing F-F-E flat and A-flat-G-G over the progression.
Transpose the ii-V-i to F minor: Gm7 flat 5-C7-Fm.
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Everything in chords
- Major Seventh Chord
- Dominant Seventh Chord
- Minor Seventh Chord
- Half-Diminished Seventh Chord
- Diminished Seventh Chord
- Minor-Major Seventh Chord