The second surviving son of Johann Sebastian Bach and Maria Barbara Bach, C.P.E. Bach was born in Weimar, with no less than Georg Philipp Telemann standing as one of his godfathers. By age 15 C.P.E. was participating in his father’s performances in Leipzig, and although he studied law at Leipzig University, music was always at the forefront of his activities.
Among his earliest compositions, written when he was about 17 years old, is a four-movement trio sonata in D minor for two violins (or, in the practice of the time, any treble instruments that could handle the range) and basso continuo. In the 1740s, after he had become the keyboard player for Frederick the Great in Berlin, C.P.E. revised many of his early works, including this trio sonata. (This is the only known case in which the original version survives. At one time that original version was thought to have been composed by Johann Sebastian himself, in whose posthumously organized catalog it appears as BWV 1036.)
In this revision, C.P.E. jettisoned the original opening Adagio, beginning instead with a much altered variant of the original Allegro second movement, now a more supple and less academic Allegretto, favoring descending chromatic bass lines and sensuous motivic interplay.
C.P.E. must have liked his original Largo, in the relative key of F major, as its first 18 bars appear almost unchanged as the slow movement of the new version. He expanded it, however, with a dramatic and unexpected close in F minor, abruptly tweaked to F major for the final cadence with almost Haydnesque humor.
The new finale is an entirely fresh movement, replacing a rather blunt and strenuous 3/8 Vivace with a more flowing – though nonetheless urgent – 2/4 Allegro. Combining some of Sebastian Bach’s contrapuntal ways with simpler, sweeter elements then coming into vogue, the new movement is in a very progressive binary form, with different endings for the repeats of each half.
— John Henken