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A diminished triad is two minor thirds stacked:
C–E♭–G♭: C to E♭ is a minor third, and E♭ to G♭ is a minor third again
Its difference from the major and minor triads lies in the fifth: in both of those, root to fifth is a perfect fifth, while here it is a diminished fifth — half a semitone narrower.
That one semitone takes away the stability:
| Element | Major / minor triad | Diminished triad |
|---|---|---|
| Root to fifth | perfect fifth (7 semitones) | diminished fifth (6) |
| Internal tritone | no | root to fifth is itself a tritone |
| Impression | can stand | must move |
It is almost always on its way somewhere
The diminished triad is a functional chord: it is rarely the destination, and mostly propels the music into the next chord.
| Position | Where it resolves |
|---|---|
| degree 7 in major (vii°) | the root is the leading tone → strongly points to I |
| degree 2 in minor (ii°) | its fifth acts as a leading tone down to V |
| degree 7 in minor (vii°) | likewise, pointing to i |
A major scale contains exactly one diminished triad (on degree 7) — which is why it stands out among the seven diatonic chords: the only unstable one, the only one that must resolve, and therefore the strongest step in a cadence (see cadence and harmonic function).
Diagram: the fifth drops half a semitone
Listen: the diminished triad
Hear the block first (unstable, pushing), then press Arpeggio to hear where the fifth is squeezed down.
Common misconceptions
- "A diminished triad is a bad chord." It is a functional chord. Without it a cadence loses its strongest step.
- "A major scale contains several diminished triads." Exactly one, on degree 7. Minor keys usually have two (degrees 2 and 7).
- "A diminished triad and a diminished seventh are the same." Three notes versus four — see diminished seventh.
- "Add a seventh and it becomes diminished." Adding a minor seventh gives a half-diminished seventh (see half-diminished seventh); only a diminished seventh completes the diminished seventh chord.
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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
- 减三和弦 = 小三度 + 小三度，根音到五音为减五度，属和声学通则
- 大调音阶上仅第 7 级为减三和弦、小调第 2 级与第 7 级常为减三和弦，为通行和声学表述
Used for fact-checking only; all prose is original.