Half-Diminished Seventh

Seventh Chord Diminished Seventh Diminished Triad Minor Seventh Scales and Harmony

A half-diminished seventh is a diminished triad plus a minor seventh:

C half-diminished = C–E♭–G♭–B♭ (written Cø7 or Cm7♭5)

The name is historical: it is diminished only half way — the triad is diminished, but the seventh is an ordinary minor seventh. The diminished seventh is diminished at both ends (its seventh sits a semitone lower).

Chord	Triad	Seventh	Tritones
half-diminished	diminished	minor seventh	1 (root and fifth)
diminished seventh	diminished	diminished seventh	2

One tritone versus two is the entire reason it sounds milder.

Where it lives

Scale	Degree	Typical use
major	degree 7 (viiø7)	leading-tone chord resolving to I
natural minor	degree 2 (iiø7)	subdominant function resolving to V

A major scale yields exactly one half-diminished seventh — which makes it among the easiest diatonic seventh chords to recognise. In jazz iiø7–V7–i is the basic minor progression, with two seventh chords in it.

Do not confuse it with the diminished seventh

The two differ in one note — and it is the seventh, not the fifth:

	Notes from C
half-diminished	C–E♭–G♭–B♭
diminished seventh	C–E♭–G♭–B𝄫

The difference is audible: the diminished seventh hangs in the air, while the half-diminished one clearly points somewhere. It also makes a broader point: how unstable a chord is depends on how many tritones it contains.

Diagram: half diminished versus fully diminished

Listen: the half-diminished seventh

Hear how it sounds dark yet directional, then compare it with the diminished seventh.

Common misconceptions

"Half-diminished is just the diminished seventh." The seventh differs by a semitone and so does the tritone count (one versus two); the heard difference is clear.
"Half-diminished chords are rare." They occur naturally on degree 7 in major and degree 2 in minor — they are diatonic chords.
"m7♭5 and ø7 are two different chords." Two spellings of one chord: the first is pop notation, the second jazz notation.
"Any chord with a diminished fifth is extremely unstable." It is far milder than the diminished seventh. Instability tracks the number of tritones.

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Listen in the library

Scales, Arpeggios, and CadencesC13:22Scale exercises can sound a half-diminished arpeggio; against a diminished seventh the calming semitone is clearDetailsSonata in A Minor, K.175C13:50A sonata in A minor — the half-diminished seventh on degree 2 acts as a subdominant with a clear resolutionDetailsInvention 1C11:03Bach's first two-part invention — half-diminished sevenths appear as the music drives forward and resolve smoothlyDetails

All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).

Sources

半减七和弦 = 减三和弦 + 小七度（三个音为小三度、小三度、大三度），属和声学通则
大调 vii 级与小调 ii 级上自然产生半减七和弦，为通行和声学表述

Used for fact-checking only; all prose is original.

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