AUGMENTED SIXTH CHORDS

Augmented sixth chords are certain altered chords that span the interval augmented sixth when presented in a certain position. There are three types of augmented sixth chords, named after European nations: the Italian, French and German sixth chords. The next figure shows examples of these chords, in the positions in which they appear most often. We see that they span the interval of the augmented sixth, between Ab4 and F#5. 

Figure: Augmented sixth chords – the interval augmented sixth is in each chord between the notes marked in red

The augmented sixth chords in the figure are in the C major key, but they can also be in the C minor key. We shall learn that augmented sixth chords are the same in a major key and its relative minor key. In the figure, we see that augmented sixth chords contain the raised fourth scale degree and the lowered sixth scale degree. In fact, the occurrence of both of these scale degrees is the best sign to recognize augmented sixth chords.

We shall learn that although the augmented sixth chords can be viewed (and they are usually spelled so in scores) as stacks of thirds, their chord annotations are not simple. We shall start by examining the French sixth chord because it has the simplest chord annotation of all the three augmented sixth chords.