Mozart clearly thought of his C minor ôFantasiaö as a violin sonata, and there is no evidence, other than not completing it, that he ever changed his mind. Unfortunately, he wrote down only five measures of the violin part; [Abbé Maximilian] Stadler [who prepared the first publication], under time constraints, decided to ignore the violin line, or rather to absorb it - in an ornamented form - into the piano part. As we were neither under the same pressures as Stadler nor beholden to Constanze, we have restored the five existing measures of Mozart's violin part and extricated the rest of it from Mozart's and Stadler's rich-textured piano-writing. Many passages, because of their perfect three-part counterpoint, turned out to be totally natural for the two instruments, and in fact, pianists who have played the work as a solo, will find their task considerably eased by the presence of a violin. Other passages required the addition of an obbligato voice to keep the counterpoint alive. Mozart has provided us with ideal models for these techniques: his Vienna period piano-violin sonatas show a growing concern for the equal treatment of the two instruments and a versatile repertoire of devices for making that possible. Stadler, in fact, was present on the day in November 1781 when publisher Artaria appeared with the proofs of Mozart's "Opus II", the six sonatas K. 296 and 376-380; Stadler writes (Anecdotes, 1829) that he "was totally enchanted" by Mozart's "incomparable" reading of these pieces with Josepha Auernhammer on two fortepianos. With an eye to Mozart's performance practice, we have supplied melodic ornaments, left-hand octave, slurs and dynamics (those in brackets), as well as bowing and fingering suggestions. In incorporating most of Stadler's completion, we have carried over many of his ideas, as they reveal his intimate knowledge of Mozart's playingà.