This sonata consists of 2 movements only. The marvellous fantasy-like first movement (marked ‘Andante con espressione’) is all about variation. The main theme is stated several times in the major as well as in the minor key (the movement being in the so-called ‘alternating variations’ form, a favourite of Haydn’s). The music unfolds in a natural, almost improvisatory manner, exploring in detail the different registers and full sound spectrum of the then still relatively new fortepiano. A simple musical idea is repeated over and over again in different variants, the 3rd and 4th bars already being a variation of bars 1 and 2. The rhythmic variety is immense and the many rests, so important for the character and beauty of the piece, let the music breathe and give it a sense of freedom.
The second movement, a lively and powerful ‘Rondo’, is no less remarkable. It provides the perfect finale and is a good example of Haydn’s musical wit. Almost incessantly Haydn plays with the different directions the music could take, and the tiny variations in melody and articulation add an extra touch of brilliance. The virtuosic runs, chords and octaves remind us of the more weighty compositions of Clementi and anticipate Haydn’s later piano works composed in London.
Haydn’s careful dynamic markings in this sonata and his love for variation reveal the influence of the music of C.P.E. Bach and the latter’s treatise on ‘The True Art of Playing Keyboard Instruments’ (1753/1762). The sonata was composed for ‘Breitkopf und Härtel’ and is probably Haydn’s first commissioned work for Germany. It is certainly a marvellous composition, revealing a whole new side of Haydn, the keyboard composer.