Augmented 6th - Jean W. Joseph

This week we add another spice to our grab bad of composition ideas – the augmented-sixth chord.

Augmented-sixth chords are predominant function chords that feature chromatic alterations – the name comes from the harmonic interval of an augmented sixth created by its characteristic notes [ ♭6 and ♯4 ].

Key Points

The augmented-sixth chord is found in major and minor keys.
In minor key already has a flatted 6th so there will only be one accidental – In major keys you will have to alter both the 6th and 4th.
The augmented-sixth chord can be Italian, French, or German – they all differ by one note.
All variations of augmented-sixth chords feature intervals a minor third && augmented sixth.
The GER+6 is, enharmonically, a major-minor or dominant 7th, however, the spelling is important as it influences the correct voice-leading.
A quick tip to finding the augmented 6th is to go to the dominant and find the notes that are a semitone above and below it, making sure that they are spelled to reflect a ♭6 and ♯4.
The bottom and the top of the chord both resolve outward to the 5th creating an octave.
These chords do not have a root. They are identified by the inclusion of both the ♭6 and ♯4.
They are NOT assigned a roman numeral.

Variations of the Augmented-sixth Chord

It+6 – b6 1 1 #4
Fr+6 – b6 1 2 #4
GER+6 – b6 1 b3 #4
EnGer+6 – b6 1 #2 #4

Italian, French, and German augmented-sixth chords and their resolutions. The German augmented-sixth produces parallel fifths if it moves directly to a V.

Since the German augmented-sixth produces parallel fifths if it moves directly to a V, composers use the i64 chord to smoothen the transition to the V.

French augmented-sixth chord resolving to V.

Youtube Resources

Jesse Strickland uses the solfege Do – Fi – Le to help with remembering the tones in the augmented-sixth chord.

Aside from his atrocious”Bambi steak” joke, this video did an awesome job of explaining augmented-sixth chords.

This video by Music Matters goes a bit more in-depth with augmented-sixths.

There is a brief introduction before he explains the difference between the Italian, French, and German versions before he finally explains some use-case scenarios.

In the next few MusictheoryforGuitar videos, he explains each of the variations and gives specific information on how each may be used and the problems associated with each variation. He also gives chord progressions that they may be found in.