A Diminished seventh

The diminished seventh chord adds a diminished seventh (enharmonically the same as a major sixth above the root in 12-TET) to the diminished triad, producing 1-♭3-♭5-♭♭7. In equal temperament it is highly symmetric: minor thirds repeat, so any chord tone can function like a root in the right voice leading. That symmetry makes it a favorite pivot chord for modulation and a rich color in classical, jazz, and film harmony.

Construction

Four notes each a minor third apart. In Cdim7, a common spelling is C-E♭-G♭-B♭♭ (written A enharmonically).

Usage

Leading-tone diminished seventh, common-tone diminished passages, dominant preparation with a bass note a third below any chord member, and chromatic slide between diatonic harmonies.

Examples

• Classical cadential dim7 over dominant pedal
• Jazz turnaround diminished cycles
• Film scoring for creeping harmonic motion

Play

Choose spellings for readability, resolve each tendency tone deliberately, and exploit smooth half-step motion to the next chord.

Ear-training cues

Chain of minor thirds; a tight, rotating, unstable sonority with multiple implied dominants.