Augmented Sixth Chords Theory ThingsWilliam Wieland
2 pitches (the A6) resolve to the dominant by ½ step.
 raised 4 up arrow 5
 
lowered 6 up arrow 5
 
fi up arrow sol
 
leup arrow sol
 
 
All augmented sixth chords also include tonic.
Italian Sixth Chord
 
 only 3 notes (A6 + tonic)
 since it does not have 4 notes
  it has a hole, like macaroni
c: It6 V 
Beethoven Bagatelle no. 1
  (on this page)

 
German Sixth Chord *
 
 4 notes (A6 + major triad)
— reliable, like a dominant 7th
  (enharmonically equivalent)
— the cadential 6/4 avoids
  parallel fifths.
c: Gr6  V
6 – 5
4 – 3
Joplin The Chrysanthemum
  (on page 1)


 
French Sixth Chord
 
 4 notes (A6 + two M3)
— mysterious, like tritones
  and the whole tone scale
c: Fr6 V 
Joplin The Cascades
  (top of p. 4)

 
Chromaticism — EVERY part on this page either moves by half step or remains on the same tone!
Note — Augmented sixth chords may trick you. We identify chords by stacking pitches in thirds, line-line-line or space-space-space, i.e. every other letter. However, F#-Ab-C-Eb is not a common seventh chord. How can you tell? F sharp up to A flat is a diminished 3rd. (Diminished 3rds are enharmonically equivalent to major 2nds.)
DryErasedTheory - Augmented Sixth Chord Review (3:30) — awesome video by richard johnson
* Doubly Augmented
Sixth Chord
 
 another spelling
  of the German Sixth
  (enharmonically equivalent)
— used in major keys
C: Gr6  V
6 – 5
4 – 3
Ask me the “nationality”!