Of his early period, we shall notice the “Sei Sonate per Cembalo,” dedicated to Frederick II. of Prussia (1742), and the Wuertemberg Sonatas, published in 1745.  Of his middle period, the “Sechs Sonaten fuers Clavier mit veraenderten Reprisen,” Berlin, 1760, and the “Sechs leichte Sonaten,” Leipzig, 1766.  And of his latter period, the six collections of “Sonaten fuer 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:—­

[Music illustration:  (Frederick) Sonata 1.  First Movement.]

In these “Frederick” Sonatas there is as yet no tendency to enharmonic and other surprise modulation such as Bach afterwards displayed.  Then as to technique, we find here octaves and large chords comparatively rare,[61] while scale passages are more restricted.  Like Beethoven, Emanuel Bach seized hold of additional notes to the keyboard.  In 1742 his highest and lowest notes, apparently, were—­

[Music illustration]

but afterwards—­

[Music illustration]

In the introductory chapter we noted the change with regard to the number of movements of a sonata which took place between 1683, when Corelli published his first sonatas, and 1740, when E. Bach composed his first set.  Instances were given of sonatas in three movements by Corelli, but with that composer four was the normal number; with E. Bach, three.  This change came about in great measure through the concerto.  From E. Bach, we are able to show the links in the chain of development:  Bach, Haydn, Mozart, Beethoven; but though between Kuhnau, the first writer of sonatas for the clavier, and Bach, B. Pasquini wrote, as mentioned in the last chapter, sonatas in three movements, yet we have no knowledge that Bach was acquainted with them.  Kuhnau, in fact, however interesting a phenomenon in the musical firmament, is not necessary to explain the appearance of Bach.  Joh.  Sebastian Bach was undoubtedly acquainted with the “Bible” Sonatas.  He must have admired them, but he may have been afraid of the freedom of form which they displayed, and of their tendency to programme-music; and perhaps he did not speak of them to his sons, lest they should be led astray.  For, as we have already mentioned, Sebastian Bach seems to have yielded for a moment to the Kuhnau influence, but, if we may judge from his subsequent art-work, he did not feel satisfied that it was a good one.