Das Wohltemperierte Clavier I, Fuga XX

Description

Inversions and strettos pile up one after another in this four-voice A minor fugue, one of the longest works in Book I of The Well-Tempered Clavier. As No. 20 of the book, it spends a long span combining its subject in different forms. Book I, its autograph title page dated 1722, runs through all twenty-four major and minor keys.

It is a four-voice fugue in A minor and 4/4. The subject is used both in its original form and turned upside down, and the music piles up strettos, in which the next voice enters before the subject has finished. With 2,376 notes in 277 seconds it is the largest of the fugues here in both length and note count. Even so, its range stays within D2 to C6, so a 61-key keyboard is enough.

It is rated advanced. It demands the structural sense and stamina to keep track of four voices over a long span and to keep the overlapping entries audible. Many passages place the voices awkwardly for the hand, so careful fingering is essential. Start by dividing the piece into sections in the score view, then lower the playback speed and check the subject entries section by section. Sort out the four voices with the hand colours, finish each section with an A-B loop and then join them, and even a piece this long becomes manageable.

Bach's collection of preludes and fugues for keyboard, covering all 24 keys and regarded as the summit of contrapuntal writing.