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A seventh chord stacks three thirds. Keep going and you get the extended chords:
| Layers | Name | From C | Status |
|---|---|---|---|
| 3 | seventh chord | C–E–G–B (or B♭) | everyday |
| 4 | ninth chord | C–E–G–B–D | common |
| 5 | eleventh chord | C–E–G–B–D–F | conditional |
| 6 | thirteenth chord | C–E–G–B–D–F–A | conditional |
The pattern is simple: the higher you stack, the more notes exist — and the fewer you actually play, because subtraction becomes mandatory.
Why notes get omitted
| Clash | Solution |
|---|---|
| the eleventh (F) sits a semitone from the third (E) | often omit the third (the chord then sounds close to a suspended fourth) |
| the ninth is a second above the octave of the root, muddy low down | raise it an octave, or drop the root and let the bass supply it |
| a thirteenth chord has seven notes, more than the ear can separate | omit the fifth and the eleventh, keeping root, third, seventh and thirteenth |
The fifth is dropped most often: it decides the least (the third sets brightness, the seventh sets tension, the root fixes identity).
A useful rule of thumb
Third for brightness, seventh for tension, ninth for colour — the fifth goes first.
Do the subtraction in that order and you arrive at the "few notes, rich sound" voicings typical of jazz and pop.
How it differs from an added-tone chord
| Added tone | Extension | |
|---|---|---|
| Example | Cadd9 = C–E–G–D | Cmaj9 = C–E–G–B–D |
| Seventh | absent | present |
| Sound | clean, open | thicker, more complex |
One practical conclusion again: skipping the seventh skips a layer of instability (see added-tone chord).
Diagram: stack to six layers, then subtract
Listen: extended chords
Hear the ninth chord, then the added-tone chord — the difference is whether that seventh layer is present.
Common misconceptions
- "More notes means a more advanced chord." In practice extensions are played with fewer notes: high stacks demand subtraction, or the low register turns to mud.
- "A ninth chord equals an added ninth." The ninth chord contains a seventh; add9 does not (see the table above).
- "Eleventh chords are unusable." They are usable, but the eleventh sits a semitone from the third, so the third is usually omitted or the eleventh raised.
- "A thirteenth chord has thirteen notes." It has seven (root, third, fifth, seventh, ninth, eleventh, thirteenth), and after the usual omissions four remain.
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Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 延伸和弦 = 在七和弦上继续叠三度（九、十一、十三度），属和声学通则
- 高叠和弦常在排列中省略五音（有时省略其他音）以避免音程冲突，为通行和声学表述
Used for fact-checking only; all prose is original.