Minor 9th b5

Notes and formula

The formula is 1 – ♭3 – ♭5 – ♭7 – 9, or 0 – 3 – 6 – 10 – 14 in semitones. The half-diminished seventh with one note added.

The ninth is a whole tone above the root rather than a semitone. A lowered ninth over this chord would produce the Locrian sound in its harshest form; the natural one is what players actually want.

The scale it names

Locrian ♮2 — the sixth mode of melodic minor — is the scale with a lowered fifth and a natural second, and this chord is its tonic. Writing the chord is a way of asking for that scale.

Plain Locrian would give a flattened ninth instead, and the difference is audible immediately: one sounds like a chord, the other like a warning.

How to play it

On guitar the movable form is x–3–4–3–4–x with the ninth added where the hand allows; the compact version is x–3–x–3–4–3, sounding C–G♭–B♭–D and leaving the third to the bass or the piano.

On piano the useful voicing is C low, then E♭–B♭–D. The lowered fifth can be dropped when a bass player is outlining it, which is common.

Where it belongs

On the ii of a minor ii–V–i, in place of a plain half-diminished chord, whenever the arrangement has room for one more note.

The substitution is essentially free: it adds colour without altering function, in the same way that a minor ninth substitutes for a minor seventh in a major key.

Against the plain half-diminished

Cm7♭5 is four notes and slightly severe. Cm9♭5 adds the ninth and softens it without changing where it goes.

Arrangers writing for piano or guitar tend to use the larger chord; horn sections tend to leave it at four notes, since the ninth is easily supplied by whoever is comping.

Scales that contain it

Locrian ♮2, exactly. Plain Locrian contradicts the ninth, which is the chord's added note and its whole reason for existing.

This is one of the clearest chord-scale pairings in jazz: the symbol names the mode, and the mode names the chord.

Frequently asked questions