Chord Construction
Extensions — 9ths, 11ths, 13ths
Keep stacking thirds and you get extended chords. The flavor of jazz, fusion, neo-soul, and modern R&B.
Why “9” and not “2”?
When a chord extends past the octave, we keep counting numbers: 8 (octave), 9, 11, 13. The 9th is the same letter as the 2nd, but stacked an octave above the 7th. Similarly: 11 = same letter as 4, 13 = same letter as 6.
A “C9” chord includes the 7th (B♭ for a dominant) and the 9th (D). A “Cadd9” includes the 9th but not the 7th. The difference matters.
The common extended chords
| Chord | Includes | In C |
|---|---|---|
| 9 | 1 3 5 ♭7 9 | C E G B♭ D |
| maj9 | 1 3 5 7 9 | C E G B D |
| m9 | 1 ♭3 5 ♭7 9 | C E♭ G B♭ D |
| 11 (rare) | 1 3 5 ♭7 9 11 | C E G B♭ D F |
| 13 | 1 3 5 ♭7 9 13 (often skip 11) | C E G B♭ D A |
| maj13 | 1 3 5 7 9 13 | C E G B D A |
| m13 | 1 ♭3 5 ♭7 9 13 | C E♭ G B♭ D A |
| add9 / add2 | 1 3 5 9 (no 7th) | C E G D |
| 6 | 1 3 5 6 | C E G A |
| 6/9 | 1 3 5 6 9 | C E G A D |
Why we drop notes on guitar
You only have 6 strings (and usually only 4 fingers free to fret). Real-world voicings of, say, a C13 chord pick the most important notes: the root or 7th, the 3rd, and the highest extension (the 13).
Rule of thumb for “essential” notes:
- Root (or assume the bass plays it)
- 3rd — defines major/minor.
- 7th — defines dominant vs major-7th flavor.
- Highest extension (9, 11, or 13) — the “colour”.
A real C13 guitar voicing might be just: root, 3, ♭7, 13 = C E B♭ A. Four notes. Sounds like Steely Dan.
Useful “add” chords for pop and folk
- Csus2 = C D G (replaces the 3 with a 2)
- Csus4 = C F G (replaces the 3 with a 4)
- Cadd9 = C E G D (adds a 9, keeps the 3)
- C6 = C E G A (adds the 6, no 7th)
These appear everywhere in pop, folk, and ambient music. They sound colourful without being jazzy.
Try this
Play an open D major chord. Now lift your 3rd finger (high E, fret 2) — you’ve created Dsus2. Now hammer the same finger one fret higher to fret 3 (high E = G) — you’ve created Dsus4. Cycle: D → Dsus2 → D → Dsus4 → D. That four-chord wiggle is in every singer-songwriter song ever.
On voicings
Two players can play a Cmaj9 chord, voice it completely differently, and both be “right”. One might play C E G B D from low to high (close voicing); another might play C B E G D (drop-2 voicing). The choice of which notes go where is called voicing, and it’s the art that separates competent rhythm players from genuine harmonic colourists. We’ll go deep on this in Voice Leading.