Structure
Three minor thirds stacked: G#°7 = G# B D F. It is symmetrical: dividing the octave into four equal parts, there are only three different diminished seventh chords. G#°7, B°7, D°7 and F°7 have the same notes.
Dominant function
- In A minor: G#°7 → Am (vii°7). G# rises to A, F falls to E, B and D converge on C or A.
- In C major (borrowed): B°7 (B D F Ab) → C. The Ab falls to G.
It contains two tritones (G#–D and B–F): it is more tense than the dominant seventh, which contains only one. It is equivalent to a V7b9 without the root (E7b9 without E = G#°7).
Enharmonic modulation
Since every note can be read as a leading tone, the same chord can resolve to four tonics: G#°7 → A(m), B°7 → C(m), D°7 → Eb(m), E#°7 (= F) → F#(m). It is the quickest way to jump into a distant key.
Passing diminished chords (Berklee patterns)
- Ascending: C – C#°7 – Dm7 (C#°7 is equivalent to A7b9 without the root, that is, V/ii).
- Descending: Em7 – Eb°7 – Dm7.
- Common-tone: C – C°7 – C (embellishes the tonic without dominant function).
In pop and production
Diminished arpeggios in pre-drops, in action films and in metal; in gospel, passing diminished chords are everywhere.
Real example
The opening of the “Toccata and Fugue in D minor” BWV 565 (attributed to Bach) culminates in a diminished seventh arpeggio over the tonic: it is perhaps the most famous diminished chord in history, and the origin of the “villain's organ” cliché.