Beyond the Traditional Augmented Sixth Chords

One topic that comes up somewhat frequently in class is that of augmented sixth chords.  How are they spelled?  How do they resolve?  I thought I’d go over those questions quickly in a blog.

Augmented sixth chords were most popular in the romantic period of classical music.  They are traditionally used as pre-dominants, meaning they resolve to some form of dominant, which subsequently resolves to tonic.  Of course, you can add “surprises” along the way, but the expected sequence for a progression is:  1) augmented sixth chord 2) dominant 3) tonic.

Augmented sixth chords can be used in both major and minor keys.  All of the examples below will be in the key of C minor.  As such, the augmented sixth chord will resolve to the dominant G, which will then resolve to C minor.

Augmented sixth chords are named such because they all use the interval of an augmented sixth, which is enharmonically equivalent to a minor seventh.  Below is an augmented sixth between Ab and F#.

Aug-Sixth-1

The interval of the augmented sixth traditionally resolves outward to an octave.  In the case of the Ab – F# augmented sixth, the Ab will fall a minor 2nd to G and the F# will rise a minor second to G.

Aug-Sixth-2

The most common augmented sixth chords have been given nicknames inspired by nationalities:  Italian, French and German.

Italian Augmented Sixth Chord

The Italian augmented sixth chord adds the pitch a major third (or tenth) above the bass.  In this case, that means we must add a “C” to the augmented sixth chord.  Below is the Italian augmented sixth chord resolving to dominant, which then resolves to tonic.

Aug-Sixth-3

French Augmented Sixth Chord

The French Augmented Sixth Chord adds the pitches a major third and augmented fourth above the bass.  In this case, that means we must add both a “C” and a “D” to the augmented sixth chord.  The French augmented sixth chord commonly resolves to a 4-3 suspension on dominant, because the “C” and “D” pitches mentioned above are common to both chords.  Below is the French augmented sixth chord resolving to dominant with a 4-3 suspension, which then resolves to tonic.

Aug-Sixth-4

German Augmented Sixth Chord

The German Augmented sixth chord uses the pitches a major third and perfect fifth above the bass.  In this case, that means we must add both a “C” and an “Eb” to the augmented sixth chord.  The German augmented sixth chord commonly resolves to a cadential 6-4 on the dominant, as the “C” and “Eb” mentioned above are common to both chords.  Below is the German augmented sixth chord resolving to a cadential 6-4, which then resolves to tonic.

Aug-Sixth-5

Other Augmented Sixth Chords

While the above chords are the most common augmented sixth chords, other chords can be built using the characteristic augmented sixth to octave progression.  Below is a chord that is enharmonically equivalent to a half-diminished seventh chord.  It is treated as an augmented sixth chord, resolving to dominant and then tonic.

Aug-Sixth-6

Below is a chord that is enharmonically equivalent to a minor seventh chord.  It is treated as an augmented sixth chord, resolving to dominant and then to tonic.

Aug-Sixth-7