Marked Allegro, the movement, probably dates from the 1780s and is a lively and attractive movement scored for clarinet in C, basset horn, violin, viola and cello—another unusual combination of instruments. The clarinet in C is often chosen by Mozart when the key of a work is C major or F major (which here suits the basset horn), but it also has a different tone from other clarinets so instrumental colour may well have played a part in the choice. The basset horn appears not infrequently in Mozart’s music. However, it was subsequently used only rarely by composers until its revival by Richard Strauss in the first half of the twentieth century. Despite its novelty, the combination used in this quintet is a winning one and it seems quite possible that Mozart merely put the piece aside temporarily with the intention of returning to it at a later date.
The 102 bars sketched by Mozart comprise a sonata exposition, marked to be repeated. For the most part, Mozart has written a complete score, but there are a few sections where only the principal voices are indicated.
from notes by Sally Odom © 2001