Arnold Schoenberg, of course, did not write a piano sonata. At any rate, none of his works for piano bears this title. As I have suggested elsewhere, however, sonata form was much in his thoughts as he wrote the piano pieces of opus 23, and one of his last two pieces for solo piano, written five years later, is a sonata movement which should stand as a model of the integration of twelve-note technique and classical form. When Pierre Boulez, in 1952, famously condemned Schoenberg for using the old forms instead of inventing new ones that were derived entirely from serialism, he might have taken just a moment to consider the ways in which the old form is articulated in opus 33a and been ever so slightly more charitable, for in this sonata movement, as in certain pieces of op. 23, themes and sections are defined and distinguished from each other in ways that have meaning only in relation to the twelve-note technique: though the form is an old one, the several parts are defined by reference to possibilities offered by the new method.