I was reading a couple of articles about the augmented 6th chord family and what i dont get is why the augmented 6th has the tendency to function as a predominant rather than dominant. For example we're in C major. The German 6/5 would be F# C Eb and Ab, which is the enharmonical equivalent of Ab7. This chord resolves nicely to Db7 which you could see as a tritone sub dominant, which will resolve nicely to C major. Isnt it considered as a secondary dominant then?

In the examples i read that it will resolve to G more strongly because of the 4# to 5 and b6 to 5 movements preparing this dominant, in other words, acting as a subdominant.
But in this example as well you could consider it as a tritone sub dominant thus by definition acting as a dominant to a new tonic G instead of C.

Last but not least, i think it even sounds as a dominant of C, where the F# and Ab pull to the G, the C remains steady and the Eb pulls to the E. Isnt this considered dominant because the 'root' doesnt go up? (C remains the same). If so, can you deal with this by using different voice leadings?

And in general, why do i read the subdominant function everywhere, while i acts perfectly as a secondary dominant?

Thx in advance!
The augmented 6th most commonly acts as a predominant. The root resolving down a semitone and the augmented 6th resolving upwards to the same note.

Take this progression.

Cm -G/B - C7/Bb - F/A - German 6th - Cm/G - G

The german 6th would be Ab C Eb F#

Resolving like this:

F# G
Eb Eb
Ab G

or missing out the ic...

F# G
Eb D
Ab G

The example of the german 6th resolving to C is pretty much the same thing as resolving to G because it's a second inversion C chord, which in essence is merely a decoration of the V chord.

Change the F# to Gb, and have it resolve to Db7 and it will be a secondary dominant ( V of bII).

Also, your figured bass is wrong, 6/5 is a first inversion 7th chord, what you meant was 4/2, but seeing as we're dealing with aug6s here and not dominant 7ths, a german 6th with the 6th in the bass would be shown by b7/b3 in a major key.
Last edited by griffRG7321 at Jul 7, 2011,
a secondary dominant is still a predominant in that case.
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it's pre dominant but i understand what your saying, a dominant 7th of any key could just as easily be a german 6th of the leading note (or the major or minor scale based on it)