In the short autobiography that he wrote in his sixtieth year, Carl Philipp Emanuel Bach mentions a feature of his musical style that has long been admired:

This diversity pervades the music of C. P. E. Bach. Not only was Bach the great eclectic, willing to embrace whatever he found good; but also he brought to the art of variation a degree of refinement few composers have matched. An elegant and distinctive variation technique is the cornerstone of his style, both in his celebrated use of the varied reprise and within sections of a work. Rare is the phrase that receives a literal repetition in C. P. E. Bach's music.

Given Bach's inventiveness and his dislike of “excessive uniformity,” one feature of his keyboard sonatas seems curiously out of place: he insists on repetition when it involves transposition in the latter part of a sonata movement.