18b Lesson - Augmented sixth chords

Class discussion

Augmented Sixth Chords

This is a collection of notes that sound cool. It was used often enough to be given a name. If you abandon all tertian harmony and think of it as a collection of notes it makes it much simpler. They’re a bunch of notes that have interesting voice leading

Why are they called augmented 6th chords?

• the key tones make an augmented 6th
• they’re both tendancy tones

When you see any raised tone, you expect it to resolve upward. When you see a lowered tone, you expect it to resolve down. When you resolve the two tendancy tones in an augmented 6th chord they both resolve to sol of the key that leads to the dominant. It fuctions as the pre-dominant leading to the dominant.

If you invert an A6 you get a d3. The augmented 6th chord doesn’t have inversions because it can’t be a chord.

They all have a b6 and #4. They also all have 1.

Italian Augmented 6th Chord

The Italian augmented 6th chord (It+6) is spelled le, do, fi. OR, b6, 1, #4. These are 6th chords because of the interval of an augmented 6th between the b6 and #4. They have no inversion. When doubling in an Italian augmented 6th chord, you double scale degree 1.

German Augmented 6th Chord

The German Augmented 6th chord (Ger+6) has the same notes as the Italian but adds b3 (me). It is spelled b6, 1, b3, #4; or le, do, me, fi.

French Augmented 6th Chord

The French augmented 6th chord (Fr+6) has the same notes as the Italian, but adds re, or scale degree 2. It is spelled b6, 1, 2, #4. Le, Do, Re, Fi.

• because it is not tertian harmony, the notes can be in any order in any augmented 6th chord

Example Progression

Major: I - vi - It+6 - V - I Minor: i - VI - It+6 - i6/4 - V - i

• you can avoid PP5 by inserting a i6/4 between the +6 chord and V

• Using an augmented 6th chord can give you a chromatic bassline, like do la le so do in the major example.

Augmented 6th chords are used for voice leading purposes.

You don’t mark these in leadsheet because they are not triadic.

Exceptions and Extra Functions

1. If you have an augmented 6th chord, and you want to go to a V7, the #4 can go to the 4.
   • we can’t use enharmonics here because respelling the F# as a Gb in a german augmented 6th, you create a 7th chord.
   • if we are in C, that makes an Ab7. Ab7 goes to bII (or N).
   • this creates a secondary dominant to a neapolitan.
   • you HAVE TO use the F# even if it resolves down.
2. Sometimes the b3 will be written as a #2 (enharmonic equivalant) for voice leading reasons.
   • if the next chord requires it to resolve up, we can use enharmonics.
   • it sounds exactly the same, but it’s how it resolves.
3. When augmented 6th chords go somewhere other than the dominant:
   • the b6 and #4 both resolve to sol.
   • if the chord has sol it can also be a I.
4. Secondary functions of augmented 6th chords
   • an augmented 6th chord can come from any key, it doesn’t have to be the home key
   • in labeling the function, you just put what scale degree the augmented 6th is highlighting.
   • if we are in C, and a Ger+6 is going to C, you label it as Ger+6/^1.
   • in C, and a Ger+6 is going to F, you label it as Ger+6/^4.

By taking the chord out of the secondary function, it means what note we are highlighting, not what key it is coming from.