Chords & Harmony

Diminished Seventh Chord

Definition

A diminished seventh chord is four notes each a minor third apart, such as B–D–F–A♭ (B°7). Tense and symmetrical, it is built on the leading tone and usually resolves to a tonic.

A diminished seventh chord is a diminished triad with a diminished seventh added above the root, so each note is a minor third (3 half steps) above the one below it. On B it is B–D–F–A♭, written B°7 or Bdim7. It is often called a "fully diminished" seventh to set it apart from the half-diminished seventh chord. Its sound is tense, dark and dramatic, and it almost always leads somewhere.

How to build one

Stack three minor thirds: B to D, D to F, F to A♭. The seventh, from B up to A♭, is a diminished seventh: 9 half steps, the same keys as a major sixth but spelled as a kind of seventh. Keep each note on its own letter, which sometimes calls for a double flat: C°7 is C–E♭–G♭–B𝄫.

Where you find it

The chord occurs naturally on degree 7 of the harmonic minor scale: G♯–B–D–F in A minor (vii°7). It acts as a dominant. Its root is the leading tone, which rises to the tonic, while the other notes move by step, mostly downward. Composers also borrow it into major keys, so B°7 (with A♭) often leads to C major.

Grand staff in 4/4, two bars of whole-note chords. Right hand: D4 F4 B4, then C4 E4 C5. Left hand: G-sharp2, then A2. Chord symbols G-sharp dim7 and Am; Roman numerals vii°7 and i. — G♯°7 resolves to A minor. The bass G♯ rises to A, B rises to C, D falls to C and F falls to E. The tonic chord ends up with its third, C, doubled.

Four notes, equal spacing

Three minor thirds make 9 half steps, and one more minor third brings you back to the root an octave higher. The chord divides the octave into four equal parts, so its inversions sound like more root-position diminished seventh chords, and any of its four notes can be spelled as the root:

Treble staff in 4/4 with four whole-note chords: B3 D4 F4 A-flat4 labeled Bdim7; D4 F4 A-flat4 C-flat5 labeled Ddim7; F4 A-flat4 C-flat5 E-double-flat5 labeled Fdim7; G-sharp4 B4 D5 F5 labeled G-sharp dim7. — Bdim7 (B–D–F–A♭), Ddim7 (D–F–A♭–C♭), Fdim7 (F–A♭–C♭–E𝄫) and G♯dim7 (G♯–B–D–F). Each contains the same four pitch classes in equal temperament. The spelling identifies a different root, and the examples also move notes into different octaves.

That symmetry has two consequences. In twelve-tone equal temperament, there are only three diminished-seventh pitch-class collections, though voicings and spellings can differ. And each one can lead to four different tonics, depending on which note is heard as the leading tone. Composers, especially in the 19th century, used that ambiguity as a quick pivot for modulating to a distant key.

B°7 on the keyboard: B, D, F and A♭, each 3 half steps above the one before.

Practice with The diminished 7th, and compare it by ear with its half-diminished cousin in Hear the Seventh: Half-Diminished or Fully Diminished?

Common questions

How many diminished seventh chords are there?

Three pitch-class collections in twelve-tone equal temperament. C°7, E♭°7, G♭°7 and A°7 share one collection, regardless of octave and enharmonic spelling. The chords on C♯, E, G and B♭ share another; those on D, F, A♭ and B share the third.

What is the difference between dim and dim7?

Dim (or °) is the three-note diminished triad, B–D–F. Dim7 (or °7) adds a diminished seventh on top, B–D–F–A♭.