Movement to a Piano Sonata for Two Pianos in B♭ (K. 375b)
de Wolfgang Amadeus Mozart
Mozart’s Movement to a Piano Sonata for Two Pianos in B♭ major (K. 375b) is a short, unfinished surviving torso from Vienna, dating to 1782–83. At 26, newly established in the city’s musical life, Mozart was exploring the expanded sonority and conversational possibilities of two keyboard parts rather than the more common four-hands format.
Background and Context
In 1782—Mozart’s first full year in Vienna after his break with the Salzburg court—he was balancing public ambition with private music-making: composing for the theatre (Die Entführung aus dem Serail), cultivating aristocratic pupils, and writing keyboard works suited to salons and domestic performance.[2]
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K. 375b belongs to that intimate Viennese sphere. What survives is an autograph fragment for two keyboard instruments (effectively two pianos in modern performance), not a complete multi-movement sonata.[2] The source tradition is thin: the Köchel-Verzeichnis records an extant but “uncompleted work,” and IMSLP notes the holograph’s preservation in the Bibliothèque nationale de France.[2][1]
Musical Character
The fragment is laid out as a single dramatic span in two clearly labeled parts: 1. *Grave and 2. Presto*.[2] Even on this small scale, the rhetoric is characteristically Mozartian: a weighty, slow opening that seems to “set the stage,” followed by fast music that implies sonata-like momentum without arriving at a fully worked conclusion.
Writing for two separate instruments lets Mozart distribute ideas in a more orchestral way than four hands can easily manage—registers can be widened, textures doubled or antiphonal, and passages can be thrown back and forth with a sense of real spatial dialogue. K. 375b’s unfinished state makes it a marginal work in the repertoire, yet it offers a glimpse of Mozart testing precisely those two-piano resources he would master in the fully completed Sonata for Two Pianos in D major, K. 448 (1781).
[1] IMSLP work page: Sonata Movement for 2 Pianos, K.Anh.42/375b (catalog data; notes on holograph and sources).
[2] Köchel-Verzeichnis (International Mozarteum Foundation): KV 375b entry with dating (Vienna, 1782–83), status (uncompleted), and workparts (Grave; Presto).