The Piano Sonata in Bb Major, KV 333 (here arranged as the Quartet in C Major KV 333) was recently determined to be a sonata that Mozart wrote in Vienna as late as November, 1783. The Allegro's opening theme pays tribute to Mozart's childhood mentor and friend, Johann Christian Bach, whose Piano Sonata op. 17/4 begins with the same falling fifth motive. In the intimate and affecting Andante cantabile, Mozart plunges us into a tangle of chromatic dissonance, a daring passage. A rondo of unusual length, the Allegretto grazioso is a tour de force and one of Mozart's most brilliant movements for solo piano, which anticipates the extended rondo finales of the Vienna piano concertos. (From the Preface)