Dominant 9th b5
9b5
0 - 4 - 6 - 10 - 14Dom7b5 + major 9th
About Dominant 9th b5
A dominant ninth flat five chord is a dominant ninth whose fifth has been lowered — in C that is C, E, G♭, B♭ and D, written C9♭5. It combines the symmetry of a flat-five dominant with the warmth of a natural ninth, and the two properties pull in opposite directions, which is exactly why the chord is used.
Notes and formula
The formula is 1 – 3 – ♭5 – ♭7 – 9, or 0 – 4 – 6 – 10 – 14 in semitones. One alteration, and it removes the chord's anchor.
Every note belongs to the whole-tone scale: C, D, E, G♭ and B♭ are all a whole tone apart or a multiple thereof. That is unusual — most altered dominants require a scale with semitones in it.
Why the whole-tone connection matters
A scale of six equal steps has no leading tone and no perfect fifth, so nothing in it establishes a key. A chord drawn entirely from it inherits that weightlessness.
The natural ninth is what keeps the chord from sounding merely strange. It is a consonance, and it gives the ear something ordinary to hold while the rest of the chord floats.
How to play it
On guitar the movable form is x–3–4–3–3–x, sounding C–G♭–B♭–D. The third is dropped, which is tolerable because the chord's identity rests on the tritone and the ninth.
On piano the chord fits comfortably in one hand: C–E–G♭–B♭–D from the bottom up, with no note needing to be moved.
Where it appears
In impressionist writing, where whole-tone harmony is a stylistic signature. In jazz, as one of the milder altered dominants — one alteration only, and a consonant one on top.
It is common in arranged music and rare in improvised comping, because a player free to choose usually reaches for a sharper alteration.
Against 7♭5 and 9♯11
C7♭5 is this chord without the ninth: four notes, starker. C9♯11 keeps the perfect fifth and adds the raised fourth above it — six notes, anchored.
The three are often written interchangeably by people who should know better. The presence or absence of the perfect fifth is what actually decides the sound.
Scales that contain it
The whole-tone scale contains every note, which makes it the obvious and the most characteristic choice.
The altered scale fits too and adds altered ninths the chord does not have, so it changes the colour rather than matching it. Lydian dominant contains the natural fifth the chord lacks.
Frequently asked questions
What notes are in a C9♭5 chord?
C, E, G♭, B♭ and D. On guitar, x–3–4–3–3–x.
Why does the whole-tone scale fit it exactly?
Because every note of the chord is a whole tone or a multiple of one away from the root. There is no note in it that requires a semitone step.
Is it the same as 9♯11?
No. This chord replaces the fifth; 9♯11 keeps it and adds the raised fourth above. One is symmetrical and rootless, the other anchored.