Mozart, Piano Sonata in A minor, K 310, second movement, middle section (development)

recording by Ludwig Semerjian on a fortepiano built by Anton Walter c. 1790 The example below starts at 5'10" on the recording recording by Christoph Ebchenbach The example below starts at 4.36" on the recording recording by Dinu Lipatti (1950) The example below starts at 7.48" on the recording	here is the complete score of the first two movements of this Sonata (pdf)

In this fragment we find twice a very characteristic use of an altered chord (here both German augmented,: #IVdv6/5 ): The altered chord confirms the dominant of a key we just arrived at, at an important 'torque' in the form.ann In this fragment, we start in de dominant key C major; at the start this key is 'stable', though the final chord of the first phrase is an unexpeted C minor chord (in maat 37).ann From this moment things become instable, and through some sequences we finally arrive at the relative minor key, D minor (around measure 39) The dominant of D minor is confirmed by the German augmented ( #IVdv6/5 ) in measure 42; the use of the altered chord at this point underlines that arriving at the key of D minor represents an important moment in the form Approximately from measure 48 ithe home key of F major is within sight. The dominant of this key is reached in measure 51 (start of a kind of "lock on V"), and finally confirmed by the Italian augmented ( #IVdv6 ) in measre 52. This moment is of course of particular interest because the middle section ends here (the reprise starting in measure54)