for the pastime of those already skilled in this study". 20 years later, Bach compiled a second book of the same kind (24 pairs of preludes and fugues), which became known as The Well-Tempered Clavier, Part Two (in German: Zweyter Theil, modern spelling: Zweiter Teil).

Modern editions usually refer to both parts as The Well-Tempered Clavier, Book 1 (WTC 1) and The Well-Tempered Clavier, Book 2 (WTC 2), respectively. The collection is generally regarded as one of the most important works in the history of classical