The third sonata in the Mannheim set, Kv.303 is another sonata with two movements and is very different than the Kv.301 and Kv.302. This sonata is written in C major. From the point of view of technical demands, it is a more complicated sonata for the pianist than the previous in the set.
Even though it was usual to start with a fast movement, Mozart introduces the Allegro (first movement) with an Andante. A very special (almost meditative) mood is being stated by Mozart in which the violinist starts alone with an upbeat. This particular introduction is the only time that the violin has the main part or a melody in this movement. With the very fast Allegro, the pianist has a virtuosic part and is being accompanied all the way by the violin. One could definitely say that Mozart did go back to his original way of writing which was not that obvious in the first two sonatas of the 301-306 set. After the 'Molto Allegro' part, we come back to the initial Allegro that is different in both melodic and accompaniment but definitely relates to the beginning. Where the first Molto Allegro was written in G major, The second Molto Allegro stays back in the tonality of C. It again has slight changes from the first section but it can be said that it is the same thing.
The second movement is a menuetto and is typical with the emphasis on the third beat, especially in the melody. This time the violin has a more dominant role compared to the first movement. There are two main melodies that Mozart plays around with the first one being introduced by the piano and the second by the violin. In the middle part, this is reversed in which the piano plays the second melody first and then that violin before going back to the initial A part with exactly the same opening and use of instruments. A short bridge is made, instead of the second theme, and a melodic line, doubled with the interval of a decima, concludes this Sonata. Interestingly enough Mozart did not write a Trio part to substitute accompany this movement, as was the custom and was used as well by Beethoven or Schubert.