Extebded chords are chord in which a seventh chord is extended with more notes, often constructed with stacked 3rd. For example, the major 7th can be extended with a 3rd which makes is a major 9th.
Cmaj7, for example, includes the notes C, E, G, B, the Cm7 includes the notes C, Eb, G, Bb and C7 includes the notes C, E, G, Bb. To these chords more notes can be added and construct new chords such as Cmaj9, Cm11 and C7.
Chords and intervals
Chord are built in intervals and the table is an overview that illustrated this based on the chords with C as the root:
It's easy to see how the chords are expanded and stacked with 3rds. Notice that the 7th interval is flattened.
The diagrams contain only a small selection, see chord overview of specific extended chord types:
9th chords (C9)
Minor 9th chords (Cm9)
Major 9th chords (Cmaj9)
11th chords (C11)
Minor 11th chords (Cm11)
13th chords (C13)
Minor 13th chords (Cm13)
Major 13th chords (Cmaj13)
Extended chord can bring different characterictiscs to the music and are common in many styles and situtions. Here are some examples with progressions including avrious extended chord types:
Dmaj9 (XX0220) - Bm9 (X2022X) - Amaj9 (X02100)
Bm11 (777777) - Am11 (555555) - G6
Aadd9 - Em9 - Bm11 (X20230) - Asus4
Bm7 (7X777X) - E9 (X7677X) - Amaj13 (5X667X)
Emaj7/B (X22444) - A6/9 (X04420) - B11 (X21200)
Back to chord types