“Now I need to say a word to my sister about the Clementi sonatas. – Anyone who plays them can hear or feel that as compositions they aren’t very much. – There are no remarkable striking passages, except the sixth and the octaves; – and even those I am asking my sister not to spend too much time, so she will not ruin her quiet and steady touch, and lose the natural lightness, flexibility, and flowing rapidity of her hand; – after all, what’s the good of it in the end? – she’s supposed to do something no one can do, not even Clementi himself; all she will produce is some atrocious chopping and hacking but nothing else in the world! – Clementi is a Ciarlattano (1) like all Italians. - He writes Presto and even Prestißimo and alla Breve on his sonatas – and plays them Allegro in 4/4 time; – I know, I heard him play; – what he does well are his passages in thirds; – but he really sweated over those day and night in London; – apart from that he has nothing to offer – nothing whatever – he has not the slightest expression or taste – and even less feeling.”
Mozart, in a letter to his father, June 7 1783.
Cited in: Spaethling, Robert (2000) Mozart’s Letters; Mozart’s Life. London: Faber and Faber, p.394.