Postlude

In this prelude, it seems that Chopin decided to experiment with two harmonic resources:

• The II-V progression: We find this in measures: 1, 2, 3, 5, 6, 7, 13 and 14 (with tonic chords in second inversion between the chords), 15, 16, 17, 18, 19 and 21, and as a Neapolitan sixth chord in measures 24 and 33.
• Augmented sixth chord: Using this chord as an enharmonic equivalent of a dominant seventh chord, along with the chromatic movement of dominant seventh/augmented sixth chords, is probably the most significant harmonic innovation in this prelude. It appears in measures 3, 4, 7, 8 and 22.