Fantaisie-Impromptu

[4] Ernst Oster conducted a technical examination of the piece which hints at similarities between the Fantaisie-Impromptu and Ludwig van Beethoven's "Moonlight" Sonata (Quasi una fantasia), which he cites as the reason for Chopin's reluctance to publish the piece.

[6] The mystery may have been solved in 1960 when pianist Arthur Rubinstein acquired the "Album of the Baroness d'Este" which had been sold at auction in Paris.

The facts of its authenticity having been "guaranteed by the French authorities" and that it shows "a delicate care for detail" and "many improvements in harmony and style" in comparison to the previously published version, Rubinstein considered absolute proof that it is the finished work.

[7] Ernst Oster observes that the Fantaisie-Impromptu draws many of its harmonic and tonal elements from Beethoven's Moonlight Sonata, which is also in C♯ minor, and from the third movement in particular.

Two measures after the melody sets in, an abrupt run features the same notes, only one octave higher, like the cadenza in the sonata's third movement (Presto agitato).

The piece then changes to presto (although some versions of the score incorporate a coda, meaning that the original tempo of allegro agitato is repeated) where it continues in C♯ minor as before.

Dream Images (Love-Death Music) (Gemini) includes three quotations from the Fantaisie-Impromptu's middle section.