Extended Chords: 9th, 11th, and 13th Construction and Quality Identification

An extended chord is a chord built by stacking thirds past the octave — past the 7th and into the 9th, 11th, and 13th scale degrees. A triad is root–third–fifth; a seventh chord adds the 7th; an extended chord adds the 9th (e.g. Cmaj9 = C–E–G–B–D), the 11th (adds the 4th scale degree an octave up), or the 13th (adds the 6th scale degree an octave up). Each step adds one more color tone. Extended chords are the foundation of jazz, R&B, and neo-soul harmony.

All three are built by stacking thirds on top of a seventh chord; the difference is how high the stack goes. A 9th chord adds one third on top of the 7th (five notes total: root, 3rd, 5th, 7th, 9th — e.g. C9 = C–E–G–B♭–D). An 11th chord adds a second third on top of the 9th (six notes: adds the 4th, e.g. C11 = C–E–G–B♭–D–F). A 13th chord adds a third third on top of the 11th (seven notes: adds the 6th, e.g. C13 = C–E–G–B♭–D–F–A). The 13th is the fullest standard extended chord — every note of the scale stacked in thirds.

All three add the same 9th color tone on top, but they differ in the 3rd and 7th underneath. Major 9th (maj9): major 3rd + major 7th (Cmaj9 = C–E–G–B–D, smooth and pretty). Dominant 9th (9, written as just a number): major 3rd + minor 7th (C9 = C–E–G–B♭–D, bluesy and tense — the V chord in jazz ii–V–I). Minor 9th (m9): minor 3rd + minor 7th (Cm9 = C–E♭–G–B♭–D, warm and funky — the ii chord in a minor ii–V–i). The 9th is the same D in all three; the 3rd and 7th decide the family.

All three have movable and open shapes. Cmaj9: a common open shape is x-3-2-4-3-x (C–E–B–D) or the movable shape 8-x-9-9-9-x (barred from the 8th fret). C9: an open shape is x-3-2-3-3-x (C–E–B♭–D–G) — the '60s soul shape. Cm9: a movable shape is 8-x-8-8-7-x (C–E♭–B♭–D–G). All three share the high D (the 9th) on the B string; the difference is the 3rd and 7th on the middle strings. The dominant C13 shape x-3-2-3-3-5 adds the 13th (A) on the high E for the full stacked sound.