It is customary to speak _en bloc_ of Emanuel Bach's sonatas; if,
however, the earlier be compared with some of the later ones,
interesting differences may be detected, and developments traced. But
the composer's artistic career, unfortunately, does not show a steady,
regular advance such as we find in J.S. Bach or Beethoven. C.H.
Bitter, his biographer and enthusiastic admirer, has to confess that
he was a practical man, and that he wrote at times to please pupils
and amateurs; while, occasionally, his aim may have been pecuniary
gain.

Of his early period, we shall notice the "Sei Sonate per Cembalo,"
dedicated to Frederick II. of Prussia (1742), and the Würtemberg
Sonatas, published in 1745. Of his middle period, the "Sechs Sonaten
fürs Clavier mit veränderten Reprisen," Berlin, 1760, and the "Sechs
leichte Sonaten," Leipzig, 1766. And of his latter period, the six
collections of "Sonaten für Kenner u. Liebhaber," published at Leipzig
between 1779 and 1787. With regard, however, to the last-named, it
must be remembered that some are of a comparatively early date. Thus
the 3rd Sonata of the 3rd Collection, one of the finest of Bach's
works, was composed in 1763, while the collection itself only appeared
in 1781. But a table of dates will be given further on.

If some of the best sonatas written after 1760 be compared with those
of 1742, there will be found in the later works more character in the
subject-matter, also movements of greater length. Practice, too, had
improved the composer's style of writing. The later Bach did not
return to the principal theme in such a crude, nay, lawless, fashion
as the following:--