Extended chords — 9ths, 11ths, 13ths
A triad stacks two 3rds. A 7th chord stacks three. Keep going — stack a fourth, fifth, sixth 3rd — and you get extended chords: 9ths, 11ths, 13ths. This is the lush vocabulary of jazz and late-Romantic music. Mostly a reference for now.
Just keep stacking thirds
Building up from C:
| Chord | Notes | The added note is… |
|---|---|---|
| C (triad) | C E G | — |
| C7 | C E G B♭ | the 7th |
| C9 | C E G B♭ D | the 9th (= the 2nd, an octave up) |
| C11 | C E G B♭ D F | the 11th (= the 4th) |
| C13 | C E G B♭ D F A | the 13th (= the 6th) |
A C13 contains seven notes — the whole scale, basically. In practice players leave some out (the 11th usually), and a violinist would only ever sound two or three of them at once.
maj, min and dominant versions
Each extension comes in flavours, following the 7th it's built on:
- Cmaj9 — built on Cmaj7 (natural 7th): C E G B D. Warm, still.
- Cm9 — built on Cm7: C E♭ G B♭ D. Mellow.
- C9 — built on C7 (dominant): C E G B♭ D. The one that wants to resolve.
Why a violinist cares
You'll see these symbols on jazz and pop charts. The practical read: an extended chord is still doing the job of the triad underneath it — a C13 is still a dominant chord pulling toward F. The extensions are colour; the bottom of the stack is the function. When you play a melody over "Dm9 – G13 – Cmaj9", it's just ii – V – I with extra paint.
The usual mistake
Being intimidated by a symbol like "B♭13♯11". Read it from the bottom: B♭ dominant chord (so it's a V of something), plus a pile of colour notes. The root and the 7th tell you what it does; the rest is decoration you can mostly ignore as a single-line player.