Jean Muller writes: "Mozart's piano sonatas are, according to Charles Rosen, actually quite fully fledged Classical compositions which are in no respect inferior to his works in other genres. Even in the few sonatas composed for pedagogical purposes, the dramatic genius of Mozart that had been sharpened by opera reveals itself. In all his sonatas the astounding, simply inexhaustible melodic richness is perfectly balanced by clear proportions and an osmosis between form and content, and with a dreamy, almost playful lightness. In the two minor-key sonatas, on the other hand, Mozart is shockingly tragic, unexpectedly uncompromising, and on a par with Beethoven in terms of dark, surging power. One particular aspect, however, seems to me to be frequently neglected: the typical Mozart humour. Capricious, mischievous, childish, playful, parodying, affectionate etc - there are not enough adjectives to describe the wit of Mozart. Astonishingly, this humour never has a hurtful or injured tone but is, on the contrary, always deeply gracious and humanistic. The emotional spectrum of Mozart's humour, with all it's diversity, is always focused on the light."