C. P. E. Bach and the fine art of transposition

Summary

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:

Since I have never liked excessive uniformity in composition and taste, since I have heard so many and so many different kinds of good things, and since I have always been of the opinion that, no matter where it might be hidden, and even if we come across it only in the slightest degree, something good can be got from a piece – these, along with my God-given talent, are presumably how the diversity (Verschiedenheit) arose that people have noticed in my music.

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.