Contemporary Orchestration Techniques

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 (possibly in the form of a suspension or a deceptive cadence), 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#.

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.

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 base.  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.

French Augmented Sixth Chord

The French Augmented Sixth Chord adds the pitches a major third and augmented fourth above the base.  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.

German Augmented Sixth Chord

The German Augmented sixth chord uses the pitches a major third and perfect fifth above the base.  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.

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.

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.