The third movement of Mozart's piano sonata K. 333 in B flat major is written in fairly standard sonata-rondo form of the classical period. Its interest lies not just in the graceful, lilting melodies so typical of Mozart, but in the engaging chromaticism, the treatment of the themes in the development, and the cadenza after the recapitulation.
The development is divided into four distinct sections in differing keys and motivic interest. The first (mm. 64-76) consists of new thematic material, and begins in G minor. Through the course of just twelve measures, Mozart modulates to E flat minor, F major, and then to B flat major, which then sets us up for the second section (mm. 76-90) in E flat major. This section uses transitory material from the primary theme of the exposition and expounds upon it, taking the basic melody and changing the rhythm. The third section (mm. 91-104), takes the primary melodic idea and reiterates it in B flat minor. As the music prepares the listener for the recapitulation, it shifts into B flat major using material from the closing section of the exposition (mm. 105-111). There is a two measure chromatic scale that serves as a link from the development to the recapitulation.
The recapitulation (mm. 112-163) is not as similar to the exposition as one might expect. There are extensions of sixteenth note scales and embellishments on all of the themes and transitions. Where the closing theme would normally be in the recapitulation, there is a retransition (mm. 164-171) using the same rhythmic pattern as the closing theme, but a different melodic idea. This carries us in to a most unique portion of the sonata: the cadenza (mm. 171-198).
This cadenza, which is an anomaly in Mozart's sonatas, functions as a sort of second development, and further augments the primary and closing themes. A snippet of the primary theme is played twice, on