Second phrase, measures 5 to 8

A descending chromatic movement in the bass leads us from the tonic to the dominant in measures 5 and 6. The following image shows a traditional version of this progression, as well as Chopin's version:

In Chopin's version, the diminished seventh chord on the third beat of measure 5 is written as C minor's seventh degree, but resolves to a G minor chord. In jazz, this type of chord movement is called a passing diminished seventh chord. Note that this chord can also be written as an Ab diminished seventh chord that descends by a half step to G minor.

We find many examples of this chord in the music of Antonio Carlos Jobim (an admirer of Chopin). Here are some measures from Vou Te Contar:

Here is an example of this chord connecting two minor seventh chords:

The second chord in measure 5 could be analyzed as a Neapolitan sixth chord (C-Eb-Ab, key of G minor) that resolves to a dominant chord (C-D-F♯). The B natural in the bass would be a chromatic passing tone.

The melodic movement from Ab to F♯, which is typical of the Neapolitan sixth chord, is repeated harmonically in the next measure as part of the augmented sixth that leads to the dominant:

The C minor key is established in measure 7. In measure 8, Chopin uses the D-flat major chord again, but this time as a Neapolitan sixth chord in root position. It was used in measure 2 as the IV degree of A-flat major.

The second phrase is repeated to conclude the prelude.

Robert Ståhlbrand, piano. Courtesy of Piano Society