The Well-Tempered Clavier II BWV 870-893 - 48 Preludes & Fugues.
Johann Sebastian Bach's idea of composing a collection of preludes and fugues in all major and minor keys was new and revolutionary in the second decade of the 18th century, particularly when considering that the tuning in use up top then distributed pure and “impure” intervals irregularly throughout the keys. The result was that one could play very well in many keys, but not at all in others. Bach was the first composer to conquer the entire breadth pf tonality in his Das Wohltemperirte Clavier (The Well-Tempered Clavier), thus providing the musical world with a masterpiece of keyboard literature.
”The ‘Well-Tempered Clavier’ is the Old Testament, Beethoven's sonatas the New. We must believe in both.” Hans von Bülow
The preludes and fugues of “The Well-Tempered Clavier” embrace an entire cosmos of compositional devices and musical characters – the “ne plus ultra” of ‘unity through diversity’. Here Bach not only presented the sum total of keyboard artistry in his day but foresaw its future evolution. His treatment of the keys marked a turning point in music history.