Piano Forum

Thank you for your comments! Now I think I can see something. Measure 22 ends with a D dominant 7th chord, that is obviously a German Aug6th. Measure 23 is the I64. What follows is tonal ambiguity, as you suggested. But I think the ambiguity is mainly between f# and A major. This ambiguity is suggested in measure 7 also, and at the very end of the piece After those 2 measures (23 and 24), the cadencial I64 is restated, followed by V7 and i, to finish the theme. Something similar happened in measures 9 and 10, when a German Aug 6th was followed by a I64 in Bb major, but, with a dominant pedal, appeared a sequence (V/ii - ii - V/iii - iii), and only after those 2 measures came V7 and I, though there followed a new sequence (V/I - I - V/vi - vi - V/iv- IV- V/iib - iib).
I think those constant changes in tonality are to reflect something like a ship trying to hold on in a storm. For example, measures 3 and 4, and measures 7 and 8 are a kind of storm that makes it impossible to know where you are. The coda is a kind of calm sea after the tempest. The prelude is in ternary form, with a compound period followed by a continuation (from measure 9) and the return of the first part, followed by a coda. A major keeps appearing from time to time, and this must be for some reason. I know that Chopin commonly makes use of some ambiguity with the relative major (the scherzo in Bb minor/D major, for example. Or the First Ballade, when Bb majors keeps appearing in the first theme).