Diminished Seventh Chord

The Diminished Seventh Chord is a four-note chord composed of a root, minor third, diminished fifth, and diminished seventh (equivalent to a major sixth). Its most distinctive characteristic is its symmetrical structure: it is composed of a series of superimposed minor third intervals. This means that every inversion of the chord has the same notes and intervals as a diminished seventh chord based on another root (e.g., Cdim7, Ebdim7, Gbdim7, Adim7 have the same notes). Its sound is extremely 'tense', 'unstable', and 'dramatic', with a strong impetus to resolve. It is ubiquitous in jazz, classical music, and film scores for its ability to create intense tension and fluid, surprising harmonic transitions. It often functions as an altered secondary dominant chord or as a passing chord to various stable chords, typically resolving to a I, V, or Imaj7.

Common Progressions

• vii°7 - I (the most common resolution, where the diminished seventh on the seventh degree of the harmonic minor scale resolves to the tonic)
• As a substitute for a V7b9: a V7b9 can be 'substituted' by a dim7 built on the third, diminished fifth, or diminished seventh of the V7b9 (e.g., G7b9 can be substituted by a Bdim7, D#dim7, or Fdim7)
• Chromatic passing chord: used to connect two chords a semitone or whole tone apart, such as C - C#dim7 - Dm7.
• In classical music and jazz ballads, to create a sense of deep melancholy or suspense.