Ninth chord
Chord with an added ninth.
What it means
A ninth chord arises when a further third is added to a seventh chord, so that a ninth lies above the root. It thus comprises five different notes. The ninth can be major or minor, which considerably changes the sound.
Musical use
Most often the ninth chord appears as a dominant: the dominant seventh chord with an added major ninth sounds full and colourful in major, with a minor ninth more tense and dark in minor. In function theory it is designated accordingly as D7 with a ninth.
Since five notes cannot be fully accommodated in four-part writing, the fifth is usually omitted. If the root is additionally omitted, what remains of the dominant ninth chord is a seventh chord above the leading tone: with a major ninth the half-diminished, with a minor ninth the fully diminished seventh chord. This interpretation explains why both sonorities work as dominants and resolve into the tonic.
In classical part-writing the ninth usually appears as a suspension that resolves downward into the octave; as an independent sonority, the ninth chord becomes established above all in the late nineteenth century. In jazz, ninths belong among the common chord extensions, and corresponding chord symbols are usual there.
For the sound, the position is decisive: the ninth should be set wide above the root. In close position it becomes a harsh second-clash.
In function theory, the dominant seventh-ninth chord is the most common form, with a major ninth in major and a minor ninth in minor. Often the root is omitted, so that a diminished seventh chord or a half-diminished sonority results. In jazz the ninth belongs among the optional tones and is notated as 9 or as an altered ninth. In Impressionist music, ninth chords are often shifted in parallel motion without being resolved.
Performance practice
Set the ninth on top and leave enough distance between it and the root. Resolve ninth suspensions distinctly downward. And with abbreviated forms, determine which note is omitted — that explains where the sonority leads.