In Chopin's Nocturne in Bb minor, Op. 9, No. 1, m. 19, b. 4-6, we have a left-hand arpeggio comprising, in order, Db2 - Ab2 - Db3 - Abb3, while the right hand plays Fb.

This harmony sits between Db major on beats 1–3 and Ab7 over a Db pedal tone in the next measure.

Example mm. 19–20

Measures 19–20

There are at least two interpretations for this:

  1. Db minor with a non-harmonic Abb3 as a chromatic passing tone between the preceding Ab3 and upcoming Gb3.
  2. Gdim7 (i.e., Abbdim7), over an Ab pedal tone, as a leading-tone chord moving to Ab7.
  3. Something else...?

In functional harmony terms, how is this chord/passage best interpreted, and why?

2 Answers 2


I think we could propose another reading, or at least provide some more nuance to current ones.

A few measures later, Chopin plays a very similar chord, but here the lower A♭ is replaced with A♮. Enharmonic spellings notwithstanding, the chord is otherwise exactly the same, and it's used to push towards D major.

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This D major holds a much larger significance: the piece is in B♭ minor, this middle section is in D♭ major, and here suddenly is this brief ray of sunshine in D major. I would argue that this D♭/D♮ dichotomy is a major part of the work, culminating in the sudden major tonic chords (with D♮ as the third, not D♭) at the end.

Perhaps this is too much of a stretch, but I view the chord that you're mentioning as an early part of this D♭/D♮ narrative. Because the F♭/A♭♭ chord is "wrong," but then it's suddenly "right" when it goes to D major, just as the piece ultimately ends with the move away from D♭ and towards D as the chordal third.

  • This is really making me take a closer look at the piece. It's full of these sorts of half-step harmonic shifts. In particular, there is a Bbb to Ab (5 of Db major) motion followed by Bbb to A-natural (3 of F major) in mm. 6–8 that is suggestive of exactly the kind of dichotomy you're describing. I've been taking them rather for granted, rather than thinking of them as structural.
    – Aaron
    Sep 10, 2022 at 2:24

I think the A♭♭ which shifts the upper structure from D♭m to D♭m♭5 deserves more harmonic dignity than merely a passing note.

I guess we've no problem with the Db pedal note that extends through these two bars. Can you accept a pedal CHORD - well, at least the outline of one in the D♭ - A♭ open 5th? Or shall we go the whole hog and call it a polychord - D♭m♭5/D♭5?

(Pop songs sometimes do this sort of thing. Keep a 1 - 5 vamp going in the bass while the upper harmony or melody modifies the 5th of the chord. When I think of a good example I'll come back and quote it...)

  • I think "pedal chord" actually comes pretty close. I see the measure as all DbMaj — so a pedal in that sense — with the Abb and Fb "alterations" moving us toward Db7. More or less the definition of passing tones, but in a slightly different light.
    – Aaron
    Sep 10, 2022 at 2:21

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