21.2: Types of Augmented Sixth Chords
There are three general types of augmented sixth chords—the Italian augmented sixth chord (“ItIt+6”), the French augmented sixth chord (“FrFr+6”), and the German augmented sixth chord (“GerGer+6”). These geographic labels have persisted throughout the years despite the fact that no reasoning has been found for these designations. 1
All types of augmented sixth chords contain scale degrees ♭6^ and ♯4^ . To these two scale degrees, the ItIt+6 adds 1^ . The three notes of the ItIt+6 (♭6^ , ♯4^ , and 1^ ) form the foundation of the FrFr+6 and GerGer+6. The FrFr+6 adds 2^ to the Italian augmented sixth chord's ♭6^ , ♯4^ , and 1^ , and the GerGer+6 adds ♭3^ to the Italian's ♭6^, ♯4^ , and 1^ , as is shown in the example below.
The final chord on the first line—the Enharmonic German +6 or EnGerEnGer+6—respells the ♭3^ as a ♯2^ because the EnGerEnGer+6 resolves only to major II46. The EnGerEnGer+6 does not occur in minor.