Half-Diminished Chord

Take a minor seventh chord and drop the fifth by a half step, and you get the half-diminished chord — a sound that’s darker and more unsettled than plain minor, but not as unstable as a fully diminished chord. It exists to do one job supremely well: be the ii chord in a minor key, leaning hard into the V7 on its way home. Almost every minor-key ballad you love uses it in the first four bars.

Building it: diminished triad plus a minor seventh

Start from a diminished triad (1–♭3–♭5) and stack a minor 7th on top instead of the double-flat 7th a fully diminished chord would use. That single difference — ♭7 versus ♭♭7 — is the whole story of “half” diminished: half the tension of the fully symmetrical Diminished Seventh Chord, twice the usability.

Formula: 1 – ♭3 – ♭5 – ♭7
Interval stack: minor 3rd – minor 3rd – major 3rd
Bø7 = B – D – F – A
Dø7 = D – F – A♭ – C
Eø7 = E – G – B♭ – D
Fø7 = F – A♭ – C♭ (= B) – E♭

Bø7 — the half-diminished stack

Ab7

Fb5

Db3

Two minor thirds, then a major third up to the natural minor 7th — a fully diminished chord would stack a third minor 3rd to A♭ (♭♭7), and that one top note is the whole "half" in half-diminished

Here are all four spelled out as chords:

You’ll see this chord written two ways in chord charts: m7♭5 (spelling out the alteration) or ø7 (the classical “half-diminished” glyph). They are the exact same chord — pick whichever your fake book uses and don’t overthink it.

Where it lives diatonically

Every major scale and its relative minor generates one half-diminished chord for free, built entirely from diatonic seventh chords:

In major: viiø7, built on the 7th scale degree (Bø7 in C major)
In minor: iiø7, built on the 2nd scale degree (Dø7 in C minor)

The viiø7 in major is a shy character — it mostly shows up passing through turnarounds. The iiø7 in minor is the star. This is the chord minor-key harmony revolves around, because minor keys need a ii chord with a flatted fifth to set up the dominant properly — a regular m7 doesn’t have the right pull.

The star turn: ii in the minor ii-V-i

The Minor ii-V-i is arguably the single most important progression in the jazz standard repertoire, and the half-diminished chord is always its opening move. The ♭5 of the ii chord voice-leads smoothly down into the altered tones of the V7, tightening the harmonic pull toward the tonic in a way plain minor never could.

Dø7 – G7♭9 – Cm (minor ii-V-i in C minor)
Dø7 – G7♯5♭9 – Cm6 (same progression, dominant more heavily altered)

Here’s that minor ii-V-i voiced as block chords:

Compare this to a major-key The ii-V-I Progression built from a plain m7 — the difference in color is the whole point. The altered dominant that follows almost always includes a ♭9, and that’s not a coincidence: the half-diminished chord primes your ear for it.

The most famous instance in the standard repertoire is the opening of Stella by Starlight, which begins on Eø7 moving to A7 — a minor ii-V aimed at D minor that never actually resolves there before the tune pivots elsewhere. It’s the textbook case every teacher points to, and for good reason: it’s four bars, and it teaches you the whole progression.

Picking a scale: Locrian versus Locrian natural 2

The obvious chord-scale choice is Locrian Mode — the 7th mode of the major scale, spelled 1–♭2–♭3–4–♭5–♭6–♭7, which matches the chord tones exactly. But in a real minor ii-V-i, straight Locrian’s ♭2 clashes against the ♭9 you’re about to hear on the V7, so most players instead reach for Locrian Natural 2 — the 6th mode of The Melodic Minor Scale, which raises that 2nd degree and smooths the line. For Dø7 resolving toward G7, that means thinking F melodic minor.

Don’t over-engineer this in performance, though: in practice, a lot of the “chord-scale theory” collapses into just knowing the arpeggio and a few passing tones — the scale choice matters most for slower, more exposed lines.

♫ Listen

Miles Davis Quintet — “Stella by Starlight” (recorded 1958, on the '58 Sessions): Bill Evans’ comping under the opening Eø7–A7 is a masterclass in voicing this chord without it sounding muddy — listen to how little he plays.
Sonny Rollins — “You Don’t Know What Love Is” (Saxophone Colossus, 1956): a minor-key ballad built on repeated minor ii-V-i motion; track the half-diminished chord each time it recurs in the melody’s opening phrase.
John Coltrane — “You Don’t Know What Love Is” (Ballads, 1962): the same changes at a slower, more rubato tempo — a good side-by-side with the Rollins version to hear two very different phrasing approaches over the same iiø7–V7♭9 motion.