Level 2 · Lesson 11
Chord Extensions
9ths, 11ths, 13ths — stacking thirds beyond the 7th to enrich harmonic color.
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Pause Culture · Chord Extensions
Bill Evans (1929–1980)
Bill Evans had studied Ravel, Debussy, and Chopin before joining Miles Davis in 1958. When Kind of Blue was recorded, Evans introduced a radically new voicing style: 9ths in inner …
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À retenir : A 9th doesn't 'replace' a chord tone — it enriches it. The difference between a chord and a color is often just one note an octave higher.
Extensions: 9th, 11th, 13th
A basic chord (triad or tetrad) can be enriched by extensions: we continue stacking thirds beyond the 7th. The 9th is the 2nd an octave higher, the 11th is the 4th an octave higher, the 13th is the 6th an octave higher.
The chain of thirds: root → 3rd → 5th → 7th → 9th → 11th → 13th. Each step adds a third. A complete 13th chord contains 7 notes — the entire scale at once. In practice, several are omitted to maintain clarity.
Click an extension to hear it and see its details.
Summary
| Extension | Symbol | Formula | Color | Semitones |
|---|---|---|---|---|
| Major 9th | Maj9 / 9 | 1–3–5–7M–9M | Warm | 14 |
| Dominant 9th | 9 | 1–3–5–♭7–9M | Open jazz | 14 |
| ♭9 | 7♭9 | 1–3–5–♭7–♭9 | Very tense | 13 |
| #11 | 7#11 / Maj7#11 | 1–3–♭7–#11 | Lydian | 18 |
| Major 13th | 13 | 1–3–♭7–13 | Rich, full | 21 |