Half & Fully Diminished 7
Two tense, unstable seventh chords — one appears naturally in every major key, the other is so symmetrical it barely has a "root" at all.
Half-diminished 7 (m7♭5)
A half-diminished 7 chord is a diminished triad with a minor 7th stacked on top: 0-3-6-10 semitones. It's written m7♭5 (or ø7), and it appears naturally on the 7th degree of any major key — in C major, that's Bm7♭5, built from B-D-F-A.
Fully diminished 7 (°7)
A fully diminished 7 chord goes one step further, stacking a diminished 7th instead: 0-3-6-9 semitones. Every interval between adjacent notes is exactly a minor third — the chord divides the octave into four perfectly equal parts.
Why fully diminished 7 barely has a "root"
Because every note is spaced identically, a fully diminished 7 chord sounds the same shape no matter which of its four notes you treat as the root. That means there are really only three unique fully diminished 7 chords in all of music — each one shared by four different letter-name spellings. This symmetry makes it a favorite passing chord for modulating smoothly between distant keys.
Common questions
What is a half-diminished 7 chord?
A diminished triad with a minor 7th on top (0-3-6-10), written m7♭5 — appears on the 7th degree of a major scale.
What is a fully diminished 7 chord?
A diminished triad with a diminished 7th on top (0-3-6-9) — equal minor thirds splitting the octave into four parts.
Why is the fully diminished 7 chord considered symmetrical?
Every note is 3 semitones from the next, so any note can act as root — only 3 unique fully diminished 7 chords exist, each with 4 spellings.
How is a fully diminished 7 chord used in music?
As a flexible passing chord that can resolve into many different keys, thanks to its symmetry — common in classical modulation and jazz reharmonization.
Play diminished chords on your instrument
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