Show off your theory chops with my weekly challenge! You’ll find a new question here every Monday. Please comment to post your reply.
This week’s challenge:
This is the end of Chopin’s powerful Nocturne in C minor, Op. 48, No. 1 The excerpt begins with him shaping up to have a typical authentic cadence, but it’s shattered when we get to the red rectangle. What is the harmony there, and where does it lead us? Hint: think about how this chord should be spelled, and notice how it’s actually spelled!

Reply to post your answer, and check back on Friday, October 22 to see if you’re right!
ANSWER for 10/18/21

Chopin has taken the German augmented sixth chord in C minor and reinterpreted it as the dominant of the Neapolitan key (bII). Below at left is a typical authentic cadence preceded by a German 6th; the F sharp in the bass resolves up to G (FI up to SO in solfege) as it should. But at right Chopin has respelled that F sharp in the bass as G flat. Now the chord is no longer a German 6th, but a plain old Ab dominant seventh in third inversion, resolving to D flat Major in first inversion (N6 or bII6).

This reinterpretation is possible because a German 6th is enharmonic with a dominant seventh chord. Until you see how they’re spelled–or hear how they resolve differently–they both sound the same! Chopin’s reinterpretation of the German 6th creates a wonderfully jarring deceptive cadence, taking us to the remote world of the Neapolitan before heading back home.
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It’s spelled as V2 of Neopolitan (resolved in first inversion) but could be “heard” (alternately spelled) with the g-flat in the bass as an f-sharp, which would make it the German augmented 6th chord of c-minor. I think it is spelled correctly because of function (not the alternate structure using f# instead of the g-flat). Is this what you had in mind? Not sure.
You’ve got it! It’s enharmonic with the German 6th, but that spelling of Gb instead of F# changes everything…it’s now a deceptive cadence, going to the Neapolitan instead of right to V.
It is the V4 of N6 not
2
uncommon
Yes, it’s V 4/2 of N6. What makes it interesting, though, is that it’s enharmonic with the German 6th in C minor, so it could be seen as a reinterpretation of that chord, creating an interesting deceptive cadence. Beethoven also does this near the end of the fugue that opens his Op. 131 String quartet in C# minor.
German 6; the Gb “should” be enharmonically written as an F#.
Right! The German 6th sounds the same as a dominant 7th chord, until you see how it’s spelled (or hear how it resolves differently). Chopin took advantage of this enharmonic relationship, respelling the F# as Gb, and now he has V 4/2 of the Neapolitan!
It’s a deceptive cadence which doubles as a V7 of flat II (Neapolitan)
Way to go! And it’s all because the German 6th sounds just like a dominant 7th chord!
He’s using a German +6 followed by its IV (Db/F), which is also a properly inverted Neapolitan 6, then resolving back to G7 and cm.
Its tonic, not IV
Way to go! It was originally a German 6th, but it’s been enharmonically respelled as the dominant of the Neapolitan. It’s a really neat trick, creating an awesome deceptive cadence!