The last Sonata of Op 40, in D major, may be the most impressive of the lot. This piece, too, begins with a slow introduction, in D minor, again a grim one, with grandiloquent double-dotted rhythms above a resolute tonic pedal point. But this bleak mood is quite dissipated by the cheerful first theme of the Allegro that follows. Casually polyphonic, and set initially over a tonic pedal point, this theme moves gracefully toward the subdominant, and then—sounding for all the world like Mendelssohn—gestures toward the relative minor before safe resolution in the main key. As in the other sonatas of Op 40, Clementi is generous here with his musical ideas. We get three quite distinct and stable themes in the dominant area, and yet another new one in the development section. But the movement seems to cohere nonetheless, thanks mainly to its carefully unified harmonic scheme that involves the sort of third relations we associate with Schubert.
The Adagio con molto espressione in D minor that follows is something of a compromise between a proper slow movement and (recalling the B minor sonata of this set) an extended slow introduction to the finale. Its opening theme, one of several distinct kinds of material Clementi offers us, imitates the elegant shape and rhythmic ambiguity of the opening theme of his earlier sonata in A major, Op 33 No 1. Then comes the finale, a bright, cheerful rondo whose central episode in D minor is mainly a canon (one of Clementi’s best) based on that opening theme.
from notes by Leon Plantinga © 2010