The four duetti BWV 802–805, in the successive tonalities of E minor, F major, G major and A minor, were included at a fairly late stage in 1739 in the engraved plates for Clavier-Übung III. The second duet in F major BWV 803 is a fugue written in the form of a da capo aria, in the form ABA.

There is a sharp contrast between the two sections, which may be Bach’s musical response to the acrimonious debate on style being conducted between Scheibe and Birnbaum at the time of composition. Section A is a conventional fugue in the spirit of the Inventions and Sinfonias, melodious, harmonious and undemanding on the listener—the “natural” cantabile approach to composition advocated by both Mattheson and Scheibe. Section B is written in quite a different way. It is severe and chromatic, mostly in minor keys, with dissonances, strettos, syncopation and canonic writing—all features frowned upon as “artificial” and “unnatural” by Bach’s critics.

Prelude and Fugue in E minor, BWV 855, is the 10th prelude and fugue for keyboard (harpsichord) in the first book of The Well Tempered Clavier, composed in 1722 by Johann Sebastian Bach.

This is the 20th prelude and fugue from the Well-Tempered Clavier. The Prelude is as compact as the Fugue is expansive. Two parts zigzag in turn on two little motifs: jumpy triads and a sort of trill, which can each be extended to form rippling runs. Now and then, Bach adds chords, sometimes in blocks and sometimes in a sort of written-out legato. Here, too, he interrupts the landing towards the fundamental with a diversion that leaves the listener unsatisfied. And just like the Fugue, the Prelude closes with a pedal point, along with the triumphant return of the trill motif.