The Impromptu in B♭ major by Franz Schubert is a theme with variations. The main theme resembles a theme from the incidental music that Schubert composed for the play Rosamunde, which also appears in the second movement of his 13th string quartet.
The variations follow the classic pattern utilized and developed by Beethoven. These elements include increasing subdivision and ornamentation, and a modulation prior to a return to the tonic for the final full variation.
Here is pianist Yeol Eum Son to perform this music for you:
