Augmented sixth chord
The augmented sixth chord is an altered chord whose mark is the augmented sixth above the bass. In C minor A♭ lies in the bass and F♯ above it. Both notes strive apart by a semitone and meet in G, the root of the dominant.
- Mark
- augmented sixth above the bass
- In C minor
- A♭ (bass) and F♯
- Resolution
- A♭ to G, F♯ to G
- Types
- Italian, French, German
- Comes before
- the dominant
Two notes that strive apart
The name contains the interval that shapes the sound: between the bass A♭ and the F♯ lies an augmented sixth, an interval of ten semitones, one more than the major sixth. It has a strong tendency to expand to the octave: the low note goes a semitone down, the high one a semitone up, and both meet in G. That is the root of the dominant. The chord therefore prepares it with double leading-tone tension.
The three types in C minor
From left to right: the Italian (A♭–C–F♯, only the third in between), the French (additionally D, an augmented fourth above the bass) and the German augmented sixth chord (additionally E♭, the fifth above the bass). The names are labels used in teaching and do not denote a secure national origin.
Resolution of the German type via the six-four chord
The bass falls from A♭ to G, the F♯ rises to G: both outer voices run into the octave. The chord with G in the bass and C and E♭ above is the six-four chord, then the dominant follows. This detour avoids the parallel fifths that would arise from going straight into the dominant.
In the glossary: Six-three chord · Neapolitan sixth chord · Six-four chord
Three types
Depending on which notes lie between the outer notes, three types are distinguished.
| Type | Notes in C minor | Addition above the bass |
|---|---|---|
| Italian | A♭–C–F♯ | third |
| French | A♭–C–D–F♯ | third, augmented fourth |
| German | A♭–C–E♭–F♯ | third, fifth |
The Italian form consists of only three different notes; in four-part writing one of them is doubled. All three types contain the tritone C–F♯. The French has with the augmented fourth A♭–D a second tritone and sounds especially tart. The German form adds the fifth. The three names are labels and no evidence of national origin.
Why the German type allows modulations
On a tempered piano the German form sounds like a dominant seventh chord. A♭–C–E♭–F♯ is enharmonically the same as A♭–C–E♭–G♭, so A♭7. This enharmonic ambiguity is used for modulations: the same chord leads in quite different directions as an augmented sixth chord to G and as a dominant seventh chord to D♭. That is why it is also heard as a means of surprising progressions.
Classification
In functional theory the chord is interpreted as an altered double dominant or an altered subdominant; textbooks do not agree on this. Its position in a passage is, by contrast, fixed: directly before the dominant or before the cadential six-four chord that leads to it. In minor it is especially natural, because the lowered sixth degree (A♭ in C minor) already belongs to the natural minor scale.
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Related terms
Six-three chordNeapolitan sixth chordSix-four chordDominantCadenceSeventh chordEnharmonic equivalence
Editor: Maik Krohm · reviewed on 3 October 2026
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