section_path: Musical style/Modulation
section_name: Modulation
paragraph_text: Modulation
  
  Modulation, or changing key in the course of a piece, is another style characteristic where Bach goes beyond what was usual in his time. Baroque instruments vastly limited modulation possibilities: keyboard instruments, prior to a workable system of temperament, limited the keys that could be modulated to, and wind instruments, especially brass instruments such as trumpets and horns, about a century before they were fitted with valves, were tied to the key of their tuning. Bach pushed the limits: he added "strange tones" in his organ playing, confusing the singers, according to an indictment he had to face in Arnstadt, and Louis Marchand, another early experimenter with modulation, seems to have avoided confrontation with Bach because the latter went further than anyone had done before. In the "Suscepit Israel" of his 1723 Magnificat, he had the trumpets in E-flat play a melody in the enharmonic scale of C minor.
  
  The major development taking place in Bach's time, and to which he contributed in no small way, was a temperament for keyboard instruments that allowed their use in all available keys (12 major and 12 minor) and also modulation without retuning. His Capriccio on the departure of a beloved brother, a very early work, showed a gusto for modulation, unlike any contemporary work this composition has been compared to, but the full expansion came with the Well-Tempered Clavier, using all keys, which Bach apparently had been developing since around 1720, the Klavierbüchlein für Wilhelm Friedemann Bach being one of its earliest examples.