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An added-tone chord does this: keep the triad intact and add one more note.
Cadd9 = C–E–G–D (the major triad complete, plus a ninth, D)
The key word is "intact": nothing in the triad moves. That distinguishes it from the suspended chord (which replaces the third) and from the ninth chord (which keeps stacking thirds).
Three ways of "one more note"
| Method | Third | New note | Result |
|---|---|---|---|
| suspension | replaced | a second or fourth | major/minor becomes undefined |
| added tone | kept | a second, sixth or ninth | major/minor stays clear, with an extra layer of colour |
| extension (ninth) | kept, plus a seventh | a ninth (the fourth third) | seventh and ninth together, more complex tension |
Added tone versus stacked third
A ninth chord = five notes (root, third, fifth, seventh, ninth); an added-tone chord = four notes (root, third, fifth, ninth, with the seventh skipped).
| Chord | Notes from C | Contains the seventh? |
|---|---|---|
| Cadd9 | C–E–G–D | no |
| Cmaj9 | C–E–G–B–D | yes, B |
That difference is practical: skip the seventh and you skip an unstable note. So add9 sounds cleaner and more open than maj9, and is easier to use as a stable chord in popular music.
Why an added note does not bite
The added note usually forms a second or a ninth against the third, which ought to clash. Two things soften it:
1. Separation by register — put the added note an octave higher (D and C colliding need more than an octave between them); 2. The fifth holds things apart — the triad's perfect fifth frames the chord, so the added note sits overhead rather than colliding with the third.
Which shows that consonance depends not only on intervals but on voicing (see chord voicing).
Diagram: added tone versus stacked third
Listen: the added-tone chord
Hear Cadd9 (clean, open), then Cmaj9 (a seventh heavier, thicker). The difference is whether the seventh is there.
Common misconceptions
- "add9 and maj9 are much the same." The latter contains a seventh; the former does not. Skipping it makes add9 clearly cleaner.
- "An added-tone chord must resolve." It can be perfectly stable; the added note is colour, not tension.
- "The added note will clash with the third." It would, so voicing separates them (usually by an octave) or the fifth holds them apart.
- "Added tone means suspended." A suspension replaces the third; an added tone keeps it and adds another note. The first loses major and minor, the second retains them.
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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
- 加音和弦 = 在完整三和弦上加入非三度叠置的音（如 add9 = 三和弦 + 九度），属和声学通则
- 加音写法与"叠三度"的延伸和弦（九和弦）在构造上不同，为通行和声学表述
Used for fact-checking only; all prose is original.