Extended & Altered Chords
Extended chords add 9ths, 11ths, and 13ths on top of seventh chords, creating rich, complex harmonies used in jazz, R&B, and neo-soul. Altered chords modify these extensions with sharps and flats for maximum tension.
The Extensions
Extended chords continue stacking thirds beyond the 7th. The 9th is the same pitch class as the 2nd, the 11th equals the 4th, and the 13th equals the 6th — but calling them "9th/11th/13th" implies the 7th is included. Calling them "add2/add4/add6" means the 7th is not included.
| Chord | Formula | Sound |
|---|---|---|
| Dominant 9th (9) | [0, 4, 7, 10, 2] | Full, funky (think Hendrix) |
| Major 9th (maj9) | [0, 4, 7, 11, 2] | Lush, dreamy, sophisticated |
| Minor 9th (m9) | [0, 3, 7, 10, 2] | Smooth, R&B, neo-soul |
| Add 9 (add9) | [0, 4, 7, 2] | Open, sparkly, pop |
| 13th (13) | [0, 4, 7, 10, 2, 9] | Big, funky, jazzy |
The add9 chord deserves special mention — it is a triad plus a 9th without a 7th, giving it a brighter, more pop-friendly sound. "Every Breath You Take" by The Police opens with an add9. The distinction between "9" (includes 7th) and "add9" (no 7th) is one of the most commonly confused points in chord notation.
Altered Dominants
Altered chords are dominant 7ths with sharped or flatted extensions. The 7#9 (the "Hendrix chord" from "Purple Haze") contains both a major 3rd and a minor 3rd disguised as a sharp 9, creating raw, aggressive tension. The 7b9 creates a powerful pull in minor-key resolutions. These chords are most common in jazz, blues, and funk.
Sixth Chords
Sixth chords add the major 6th (9 semitones) to a triad, creating a warm, vintage sound. The major 6th [0, 4, 7, 9] was the default chord in the swing era. The 6/9 chord adds both the 6th and 9th for a rich, luxurious resting chord common in jazz endings.
In ChordColor
ChordColor includes all extended and altered chord types across all 12 roots. The color system treats extensions by their pitch class — the 9th shows orange (major 2nd), the 11th shows lime-green (perfect 4th), and the 13th shows purple (major 6th).