Sonata in C major, K. 330.
Light returns in Mozart's work, after the darkness of his Sonata in A Minor.
"The sonata appears 'lighter' than the preceding one, but it is just as much a masterpiece, in which every note 'belongs' - one of the most lovable works Mozart ever wrote. In it the shadows of the Andante cantabile give place to an unclouded purity; a particularly delighful feature is the way the second part of the Finale begins with a simple little song".
When Einstein writes that "every note 'belongs'", what he actually means is that every note is in its proper place; we simply cannot imagine a different melodic course, therefore it is impossible to "alter" the score in any way...One cannot alter what is perfect...
Here is a live performance of this Sonata, played by Daniel Barenboim.