The dominant ninth chord in harmonic writing: major, minor and incomplete · Harmony lessons

Definition

The dominant ninth chord is obtained by adding to the V7 a third above the seventh: in C major G–B–D–F–A (major ninth). With the minor ninth (Ab) you get the dominant minor ninth, proper to the minor mode but also used in major as a borrowed chord. In classical and Romantic music the ninth is treated as a dissonance with precise rules; in jazz and funk it becomes a stable color.

Four-voice spacing

Since there are five notes, in four voices the fifth is omitted (D):

Bass: G (root)
Upper voices: B (third), F (seventh), A (ninth)

Spacing rules:

the ninth must lie at least a ninth above the root (never at the distance of a second);
the ninth is preferably placed in the soprano;
the ninth must not be placed below the third (the leading tone), so as not to create a dissonant seventh with it.

Resolution

Ninth → fifth of the tonic by descending step (A → G), together with the rest of the chord: B → C, F → E.
Ninth → octave before the chord change (A → G over the same G in the bass): the ninth behaves like an appoggiatura or a 9-8 suspension and the chord becomes a V7 that then resolves normally.
The minor ninth (Ab) falls in the same way toward G.
Inversions of the ninth are rare in the classical style; the ninth never goes in the bass.

The incomplete ninth: vii°7 and viiø7

Removing the root from the V9 gives two chords you already know:

from the major V9 (G–B–D–F–A): B–D–F–A = viiø7, the half-diminished seventh of the major mode;
from the minor V9 (G–B–D–F–Ab): B–D–F–Ab = vii°7, the diminished seventh.

This is why the leading-tone seventh chord behaves like a dominant: it is a dominant ninth without the root.

Practical rules

Prepare the ninth by step or as a common tone; entering by leap is typical of the 19th century and gives emphasis.
In major the minor ninth (Ab) brings a dramatic, dark color, very Romantic.
In orchestration the ninth in a high, isolated register (flute, violins) sounds brighter; doubled low it becomes heavy.

Typical mistakes

Placing the ninth at the distance of a second from the root: it becomes a cluster, not a ninth.
Letting the ninth rise.
Omitting the third instead of the fifth: you lose the leading tone and therefore the function.

Examples

Chopin, Waltz Op. 64 No. 1 (“Minute Waltz”): the first phrase culminates on a dominant ninth chord.
Franck, Sonata for Violin and Piano: the piano opens with a dominant ninth chord, and the violin's entrance arpeggiates its notes.
Debussy, “Hommage à Rameau” (Images, I): the climax is a broad dominant ninth, in chord and in arpeggio.
Funk and soul: dominant ninth chords as stable tonic chords, for example in “Play That Funky Music” by Wild Cherry and in many James Brown tracks.

How to use it in composition

In a Romantic ending, replace the V7 with the V9 (ninth in the soprano) for a more expressive climax.
The minor ninth in major is ideal for a moment of shadow before the bright resolution.
In pop and film music, the suspended dominant ninth (left unresolved) creates an “open” expectation.

Exercise

Write in four voices in D major: ii6 – V9 – I, with the ninth in the soprano falling to the fifth of the tonic.
Write the same in D minor with the minor ninth.
Play V9 and viiø7 in C major and verify that the second is the first without the root.

Ninth chords: maj9, 9, m9, b9, #9, add9; Extensions and tensions; Dominant seventh chord; Half-diminished seventh chord; Diminished seventh chord; Eleventh and thirteenth chords.

Sources

en.wikipedia.org