Easily one of the best sonatas among the earliest group, this work can be used as a prime example of two styles in vogue during the mid-eighteenth century: the style galante, and the Empfindsamer stil. The two outer movements are picture-perfect galanterie in the best mode, while the middle movement stands as the most distinguished of the intensely melancholic, personal, subjective products of Haydn's Empfindsamkeit.
First Movement: Moderato
The movement offers a full-bodied sonata form, including a proper transitional passage between tonic and dominant keys (no 'bifocal closes' here), clearly-delineated primary and (multiple) secondary themes, and an excellently worked-out development section. A critical aspect of this movement, clearly pointing towards the mature Haydn to come, is its use of a sixteenth-note-triplet figure which acts motivically through the movement, binding together the T, S, and K themes, even acting as a cadential formula for both 1S and 2S. Another later-Haydn technique encountered clearly in this movement is a deliberate weakening of the key prior to its firm establishment at an important thematic/harmonic juncture -- such as the arrival of 2S (at measure 48) being preceded by a 2T which a chromatic feint leading to an expanded IV6.
Second Movement: Largo
Movements such as this, with a highly ornamented melodic line unfolding gradually over a pulsating bass, represent the Empfindsamer stil that we tend to associate with composers such as C.P.E. Bach. (It's unlikely that Haydn picked up the style directly from Bach, however; Bach's keyboard music written in this idiom was not readiliy available in Vienna in 1760. Either Wagenseil or Jiri Benda's keyboard music was accessible, however, and could easily have provided abundant models.) The sheer variety of rhythmic patterns alone is far beyond anything encountered in the keyboard sonatas so far; the mood is introverted, even slightly morbid. That melancholic thread is never wholly absent from Haydn's work, although it is much less apparent to the listener (as a rule) than in the music of his brilliant younger contemporary, Mozart. (One should remember that Mozart was only a small child when this sonata was written.)
Third Movement: Menuet
After the sophisticated sentiment of the slow movement, the lighter-than-air Galant minuet is a welcome refreshment. Certainly the style may seem insipid to modern listeners, nor is there a case to be made for anything particularly special about the movement. (It's utterly foursquare and predictable.) The minor-key Trio offers a slight whiff of introspection. Given the movement's relative blandness, I have relented a bit in my stance concerning overly-ornamented repeats. Nonetheless, my mantra remains ix-nay on the udgies-bay.