Other sevenths · Seventh chords · Music theory
Seventh chords are also built on the other degrees, with the notes of the scale. Besides V⁷, two more are common in exams. The leading-tone seventh, on VII…
Other sevenths
Seventh chords are also built on the other degrees, with the notes of the scale. Besides V⁷, two more are common in exams. The leading-tone seventh, on VII in major, is a diminished triad with a minor 7th (also called half-diminished). The diminished seventh, on VII in minor, is a diminished triad with a diminished 7th: three minor thirds in a row.
Those on II and IV are diatonic sevenths: II⁷ is a minor chord with a minor 7th, and IV⁷ in major, a major chord with a major 7th. All of them resolve their 7th downward.
The sevenths of each degree
A seventh chord forms on each degree of the scale, and it is worth knowing its type. In minor, the harmonic scale is used here.
The diminished seventh, a special case
It is made of three minor thirds, so it divides the octave into equal parts: B–D–F–A♭, D–F–A♭–C♭ and its other spellings sound the same. There are only three distinct sonorities of this chord, and each can resolve in several keys.
That is why it is a classic tool for modulating, and its ambiguous sound has often been used to express surprise or drama.