It seems that by the time Wolfgang Amadeus Mozart was writing the Sonata for piano and violin in Eb (K. 481), which was just about the time he wrote The Marriage of Figaro, facile or pre-cut characterizations and constructions were no longer compositional options for him. In these later works, there is an uncanniness about how Mozart’s sense of play could control so many dimensions of a piece at once that he can have them seeming to take on lives of their own, and defining their own devices.
In the later works (and in the operas especially), there are times when musical elements or characters seem suddenly to burst into relief, or when musical ideas, inexplicably, are by music explained. The Eb Sonata has these elements at its most crucial points: in the meta-introduction and meta-conclusion of the first movement, for example, or in the sudden piano concerto at the fifth variation of the third movement. It shows an odd sort of spiraling understanding, where layer on layer of the piece shows an unselfconscious self-awareness, and awareness of all the other layers.
This is all of course very difficult to describe. But let us say at least this: the second movement, which is not only operatic but seems to play a whole scene, is extremely beautiful. The relationship between the two main themes could very fruitfully be compared to those in situations from both The Marriage of Figaro and Don Giovanni – it is formally and psychologically rich beyond its medium. Few people, in any art, have created items like this.