Sonata in C major for piano duet, K.521

Mozart’s last duet sonata, dated 29 May 1787, was apparently intended for Franziska von Jacquin, sister of his friend Gottfried Jacquin. Certainly, he gave the sonata to Gottfried and asked him to pass it on to her and to tell her to “tackle is at once, for it is rather difficult.” Later, however, he dedicated it to the Natorp sisters, Nanette and Babette, the last of whom eventually became known as the best woman pianist in Vienna. It is not for beginners. From the technical point of view, in its keyboard writing, it is the most advanced of the piano-duet sonatas. but, with its development section devoted to new material in the manner of the early sonatas, the first movement lacks the continuity of the F major Sonata.

The Andante is highly effective in its ternary design, the virtuoso middle section in the relative minor cleverly offset by the melodic formality of the f major outer sections. The same kind of melody prevails in the Allegretto, a Haydnesque construction based on the decorated repetitions of one, semi-comic theme.