18b Lesson - Augmented sixth chords

Class discussion

Augmented sixth chords

• Not based in tertian harmony, so their “Roman numerals” are written differently than normal
• They’re called augmented sixth chords because they contain an augmented sixth
• The primary reason for these is voice leading–the raised tone moves up, the lowered tone moves down. Both tones will proceed to the root of the next chord
  • a default +6 chord will proceed to V and has predominant function

Think of the components of these chords using scale degrees!

• Italian (It): b6, #4, 1 (x2)
• German (Ger): b6, #4, 1, b3
• French (Fr): b6, #4, 1, 2
• Ger+6 and Fr+6 are just It+6s with extra stuff!

Italian is the “basic” flavor: it just contains all the notes that all the +6 chords have. In my experience, I actually had more trouble IDing It+6 chords than the other two because I psyched myself out looking for a fourth tone that obviously was not there. So, be aware that It+6s are going ot have a different shape than Ger+6 and Fr+6.

Speaking of shape, Ger+6s will usually appear in the same shape as a V6/5, while Fr+6 will usually appear in the same shape as a V4/3. The default shape for a It+6 is like a V6. (V(7) is used as a filler for simplicity: remember that these all have predominant function.)

The “inversion” doesn’t affect how we label these. No matter which note is in the bass, it’s always written as the default (x)+6. This is because the chord is not made up of stacked thirds, so our inversion labeling system doesn’t translate properly.

Common fix for Ger+6 resolution: have it go to a I6/4! Also be aware that composers may enharmonically write any of the tones for voice leading purposes (again, the primary use of these chords is just cool-sounding voice leading)

Augmented sixth chords resolving to a non-dominant harmony

• By writing some notes enharmonically, we can basically sub in one dominant chord for another. In the example we did in class (in C), the respelled Ger+6 translated to a Db7, which still moved nicely over to V7.
  • Process: writing out the full chord (Db F Ab B) and respelling the B as a Cb. Cb wants to resolve down to the B in the next chord, and the F carries through to be the seventh.
• If you keep the chord as written, we have our normal +6 chord function: the actual +6 resolves outward to the root of the next chord. So our original +6 chord from the example resolves to a C major chord.
  • Labeling: instead of using our “in the key of” secondary dominant labeling, the slash indicates “going to” and you write the scale degree below the slash. The Ger+6 in this example would be written as Ger+6/^1 (remember the caret should be written above the number)
  • In this instance, Ger+6/^1 actually has dominant function, rather than predominant. It subs in for V7 and proceeds straight to I. Think of respelling the chord as a Db7! Ger+6s can have dominant function…but only sometimes

This was a lot of info, so here’s the most important things to remember:

• Tones of each kind of +6 chord
• How the different tones resolve
• Function(s) of a +6 chord