Augmented 6th Chords

Augmented 6th chords are chromatic chords that are built upon the interval of a major 3rd and an augmented 6th.
They are very useful in modulation to different keys and have been used in various forms since the Renaissance period.

Augmented sixth chords are typically built on the flattened submediant (the 6th note of the scale)
They usually occur in minor key, but can be found in major keys through use of additional accidentals to “borrow” notes from the parallel minor scale.

Augmented 6th chord

      Augmented 6th Chord

Augmented 6th chords are dissonant and so “want” to resolve.
Typically, the lower note moves down a semitone and the upper note moves up a semitone to form an octave. If this is the case then the harmony usually leads to V (or sometimes Ic-V).

Augmented sixth chords resolution

      Augmented sixth chords resolution

Types of Augmented 6th Chord

There are 3 common types of augmented sixth chords you will come across. All three of the chords include the major 3rd interval and the augmented 6th interval above the root note, but have differences in the other note added:

3 types of augmented 6th chords

      3 types of augmented 6th chords

Italian Augmented 6th

The Italian Sixth is the simplest of the three versions as it uses just the 3 basic notes from the augmented 6th chord:
Italian augmented 6th chord

      Italian Sixth

Here is a very famous example of an Italian sixth taken from Beethoven’s Symphony No. 5:
Italian Augmented 6th example Beethoven 5th Symphony

      Beethoven 5th Italian sixth example

French augmented 6th

The French sixth has an augmented 4th interval added above the bass:
French augmented 6th chord

      French sixth

Have a look/listen to this example of a French sixth from Beethoven’s Pathetique Piano Sonata:
French Augmented 6th example Beethoven Pathetique Sonata

      Beethoven Pathetique French sixth

German augmented 6th

The German sixth has a perfect 5th added instead of the augmented 4th:
German augmented 6th chord example

      German sixth

This extract from Schubert’s Waltz in C major is an example of a German sixth:
German Augmented 6th example Schubert Waltz

      Schubert Waltz German sixth example

The German sixth is the most commonly used of the three and works well as a pivot chord for modulation. The typical modulation you see is where the augmented 6th chord is built on the flattened submediant in the existing key and then leads to the dominant which becomes the new key. For example, in C the German sixth would naturally pivot the piece to G (the dominant).

However, the German sixth can also act as a dominant 7th chord of another key through enharmonic changes.

German sixth enharmonic change to minor seventh

For example, in C, the German 6th can become dominant 7th of D flat if the F sharp is rewritten as a G flat. The distance in pitch remains the same, but the interval is expressed differently and so leads to the new key:

German sixth as minor seventh progression

      German 6th as Dominant 7th

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