Diminished Major 7th

Notes and formula

The formula is 1 – ♭3 – ♭5 – 7, or 0 – 3 – 6 – 11 in semitones. A diminished triad — two stacked minor thirds — with a major seventh above it.

The chord therefore carries a tritone between C and G♭ and a semitone between B and the C above, two of the sharpest frictions available, in a single four-note stack.

Why it belongs to no key

Build seventh chords on every degree of the major, natural minor, harmonic minor and melodic minor scales and this chord appears on none of them. The diminished triad occurs in all four, but never with a major seventh above it.

That is not a curiosity, it is the whole explanation of how the chord is used. Anything that cannot be reached diatonically has to be introduced deliberately, so this one arrives as a passing sonority, as a diminished seventh whose top note has been raised, or as the by-product of a line moving underneath a held note.

How to play it

On piano it is C–E♭–G♭–B, and the semitone at the top means it needs a wide spread: root low, seventh high, or the chord simply sounds wrong rather than tense.

On guitar the workable form is x3424x with the top note raised a fret from a diminished seventh — 8–x–8–9–10–x with the root on the sixth string is easier to hold and sounds clearer.

Where it turns up

In film scoring, where the tritone and the leading tone together read as dread without committing to a key. In late-Romantic music, as a passing chord inside a chromatic descent.

And in transcription: a diminished seventh over a pedal note that happens to be a leading tone produces exactly these four pitches, and the symbol appears because the transcriber had no shorter way to write what was sounding.

Against its neighbours

Cdim7 is C–E♭–G♭–A and passes; Cm7♭5 is C–E♭–G♭–B♭ and rests; CdimMaj7 is C–E♭–G♭–B and does neither. All three share the same diminished triad, and only the top note differs.

Reading the three symbols carefully matters more here than anywhere else in the catalogue, because the sonorities are genuinely different and the notation is genuinely close.

Scales that contain it

No common seven-note scale does. The closest fit is the whole–half diminished scale with its seventh degree raised, which is a way of saying that players improvise around the chord rather than through it.

The practical approach is to treat the major seventh as a held voice and play a diminished scale under it — that is usually what produced the chord in the first place.

Frequently asked questions