Diminished 7th and minor-major 7th
Know the two seventh chords that come from the harmonic minor scale.
The harmonic minor scale of lesson 6.4 gives two more seventh chords. Both sound dark and tense.
Diminished 7th
The diminished 7th chord (also fully diminished) has the symbol C°7. Its formula is 1 ♭3 ♭5 𝄫7: C E♭ G♭ B𝄫, three minor 3rds stacked. The 𝄫7 sounds like a major 6th but is written as a 7th, B𝄫 and not A, because the chord is built in thirds (lesson 4.4). Half-diminished (ø7) and fully diminished (°7) differ only in the 7th: ♭7 versus 𝄫7.
It is symmetrical: every note is a minor 3rd apart. So there are only three different-sounding diminished 7th chords. C°7, E♭°7, G♭°7 and A°7 contain the same four pitches, spelled differently, and every one of the 12 roots belongs to one of the three groups.
| Group | Chord | Notes |
|---|---|---|
| 1 | C°7 | C E♭ G♭ B𝄫 |
| 1 | E♭°7 | E♭ G♭ B𝄫 D𝄫 |
| 1 | G♭°7 | G♭ B𝄫 D𝄫 F𝄫 |
| 1 | A°7 | A C E♭ G♭ |
| 2 | D♭°7 | D♭ F♭ A𝄫 C𝄫 |
| 2 | E°7 | E G B♭ D♭ |
| 2 | G°7 | G B♭ D♭ F♭ |
| 2 | B♭°7 | B♭ D♭ F♭ A𝄫 |
| 3 | D°7 | D F A♭ C♭ |
| 3 | F°7 | F A♭ C♭ E𝄫 |
| 3 | A♭°7 | A♭ C♭ E𝄫 G𝄫 |
| 3 | B°7 | B D F A♭ |
It occurs naturally on the 7th degree of the harmonic minor (G♯°7 in Am), and acts like a dominant: tense, resolving to the tonic.
Minor-major 7th
The minor-major 7th, symbol Cm(maj7), is 1 ♭3 5 7: C E♭ G B. It is a minor triad with a major 7th, the i chord of the harmonic or melodic minor. It sounds dark and tense, typical of film and jazz.
One more chord appears in the harmonic minor: the augmented major 7th (+maj7, 1 3 ♯5 7) on the III degree. It is rare. It is mentioned for completeness, as it appears in the Key Chords tool.
Play C°7 as an arpeggio, then move the same shape up 3 frets (E♭°7), and again. Notice that you keep playing the same four notes.