Mozart composed his second-to-last piano sonata in February 1789, but it did not become known until five years after his death when it was published as a sonata for piano and violin! This B-flat major Sonata was excluded from the solo piano sonatas until well into the twentieth century even though Mozart had clearly entered the work into his thematic catalog as “for piano alone,” and the unimaginative violin part had long been deemed spurious.

The B-flat Sonata, like its predecessor in C major (K. 545) which Mozart labeled “for beginners,” is often regarded as a teaching piece, but its outward simplicity belies a wealth of sophisticated musical thought. In the first movement Mozart employs the same material for his first and second themes—a spare, leisurely descent and ascent with a gracefully spun-out continuation—but in between he inserts a bold leaping gesture that abruptly shifts to a serene new idea. The initial stability of this idea belies its function as a transition to the second theme area. The same bold juxtaposition of the leaping gesture and the transition theme launch the development section, now diving into new harmonic territory (D-flat major).

The exquisite slow movement unfolds in a luxurious five-part rondo in which each section is a binary form with repeats. The elegant refrain sections surround two contrasting episodes, the first haunting and gently agitated in C minor and the second a singing melody with broken-chord accompaniment (A-flat major). Mozart’s coda recalls elements of both episodes.

The lighthearted final movement also adopts rondo form, but Mozart ingeniously varies what might have been an A-B-A-C-A structure—he wittily sets up expectation for the return of the refrain (middle “A”) but moves directly into the second episode (”C”). Another remarkable feature of the movement is Mozart’s continuation of the home key in the first episode instead of a more typical shift to a related key. Mozart shortens the concluding return of the refrain and adds a jolly coda based mainly on first episode material with a snippet of the second episode cleverly worked in.

© Jane Vial Jaffe