Dominant 9th

Notes and formula

The formula is 1 – 3 – 5 – ♭7 – 9, or 0 – 4 – 7 – 10 – 14 in semitones. A dominant seventh with the ninth stacked above it.

The ninth changes the chord's manners, not its job. E and B♭ still form a tritone and still resolve to F and A, so C9 goes wherever C7 goes; the added D simply gives the chord more body while it does so.

How to play it

On guitar C9 is x32333, and the shape is famous in its own right: this is the chord James Brown's guitarists played on the ninth fret and the reason a single stab of it sounds like funk before any drum enters.

On piano the root usually goes to the bass and the right hand voices E–B♭–D, or B♭–D–E in a rootless form. As with every dominant, the fifth is expendable and the third and seventh are not.

What it does in a progression

A dominant ninth resolves like a plain dominant seventh — down a fifth, C9 to F — and can be substituted for one anywhere without changing the harmonic analysis. Arrangers use the substitution to thicken a bar rather than to alter it.

It also works where a seventh alone would be too plain: as the standing chord of a vamp. A funk or soul groove that sits on one chord for eight bars is usually sitting on a ninth, because the extra note keeps the harmony interesting while nothing moves.

Where you hear it

Funk, soul and blues use it constantly; big-band writing uses it as a default voicing for a dominant in the saxophone section; gospel piano treats it as the ordinary form of a V chord.

It is rare in classical music for the same reason it is common in these styles: common practice wants dominants to resolve promptly, and the ninth is a colour that rewards being held.

Dominant ninth, major ninth and the altered ninths

C9 and Cmaj9 differ by one semitone in the seventh — B♭ against B — and by everything in behaviour: one moves, the other rests. This is the most common misreading of a chord chart with extensions in it.

Alter the ninth itself and the chord changes character again. C7♭9 and C7♯9 are dominants with the same tritone and far more bite; C9 is the version that sounds smooth. All three resolve to the same place.

Scales that contain it

Mixolydian fits without alteration and is the standard choice. Over a vamp on a single dominant ninth, players stay in it and use the ninth as a landing note rather than a passing one.

In a blues the melody often ignores the chord's major third and uses the minor pentatonic instead. That clash is not an error — it is the sound of the style — and the ninth in the harmony is what keeps it from turning harsh.

Frequently asked questions