Allegro in B♭ major for Piano (fragment; completed by M. Stadler), K. 400
沃尔夫冈·阿马德乌斯·莫扎特
Mozart’s Allegro in B♭ major for piano (K. 400; also catalogued as K. 372a) is a surviving first-movement fragment from his early Vienna years, generally dated to around 1781–1782. Preserved incomplete, it is most often heard in a later completion by the Viennese composer and cleric Maximilian Stadler.
What Is Known
The work survives as an unfinished sonata movement (Allegro) in B♭ major for solo keyboard, linked with Mozart’s early period in Vienna (c. 1781–1782, when he was 25–26). In the Neue Mozart-Ausgabe it is explicitly presented as a “Movement of a Sonata in B flat … completed by Maximilian Stadler,” underscoring that the ending heard in performance is not entirely Mozart’s own text.[1]
As an Amazon Associate we earn from qualifying purchases.
The most widely repeated description of the break-point is that Mozart’s autograph extends through the exposition and development and stops partway through the recapitulation—often given as “to the middle of bar 91,” with Stadler supplying the continuation to a performing length of roughly 148 bars.[2] This makes K. 400 an unusually clear case where the manuscript invites a practical realization rather than a conjectural “reconstruction.”
Musical Content
What remains on the page is a taut, bright sonata-allegro design, typical of Mozart’s keyboard writing at the beginning of the 1780s: a crisp principal idea, lively passagework, and a development that treats small motifs with quick modulation and rhythmic insistence. The fragment’s clean periodic phrasing and busy right-hand figuration suggest a composer freshly engaged with Vienna’s public pianism—virtuosic enough to sparkle, but still grounded in the galant clarity that underpins Mozart’s mature sonatas.[3]
In performance, Stadler’s completion is usually heard as a pragmatic, form-conscious attempt to “square” Mozart’s surviving material into a balanced recapitulation and closing; stylistically it aims to sound like Mozart by following the exposition’s cues rather than by introducing new, strongly personal themes.[4]
[1] Digital Mozart Edition (Mozarteum): Neue Mozart-Ausgabe table of contents listing K. 400/372a as a sonata movement “completed by Maximilian Stadler.”
[2] Wikipedia (French): overview noting Mozart’s text breaks off around the middle of bar 91, with the remainder completed by Maximilian Stadler.
[3] IMSLP work page: catalog identifiers (K. 400 / K⁶ 372a), key, and public-domain score access for the fragment/completion tradition.
[4] Schott Music catalogue note discussing the piece as a sonata movement and the plausibility of Stadler’s completion within sonata form conventions.