Reference : ninth chords
A ninth chord is formed by adding a ninth to a seventh chord.
The most common ninth chords are built over the dominant seventh chord in both major and minor keys. Because the ninth formed is major in major keys and minor in minor keys, these chords are called dominant major ninth and dominant minor ninth.
Dominant major 9th
Ninth chords can also be built on minor seventh and major seventh chords:
Major 7th, major 9th
The augmented or sharp ninth chord is obtained by adding an augmented ninth interval to a dominant seventh chord. In many cases, the ninth interval is simplified enharmonically. In these cases, the chord appears as a dominant ninth chord with a major and minor third:
dominant 7th, augmented 9th
We find an augmented ninth chord in Chopin's Prelude 4:
See C > Chord for related entries.
