bar a demisemiquaver motif is introduced that is developed later in the duet in a highly original way; it also serves as a means of modulation after which the parts interchange their roles. The contrasting second subject in quavers with octave leaps is a descent by a chromatic fourth. The harmonies between the two chromatic parts are similar to those in the A minor prelude BWV 889/1 from the second book of The Well-Tempered Clavier, presumed to have been composed at roughly the same time. BWV 802 has been analysed as follows: bars 1–28: exposition for 6 bars in E minor followed by 6 bars with parts interchanged in B minor, four transitional bars of the demisemiquaver motif in imitation, followed by a repeat of the exposition for 12 bars, all in E minor bars 29–56: inverted exposition for 6 bars with parts in G major followed by 6 bars with parts interchanged in D major, four transitional bars of the demisemiquaver motif in imitation, followed by a repeat of the inverted exposition for 12 bars, all in B minor bars 57–60: a transitional passage made up of demisemiquaver scales for 2 bars in D minor, then inverted for 2 bars in A minor bars 61–73: repeat of exposition for 5 bars then with parts interchanged for 5 bars, followed by a final interchange and inversion of parts for the 3 bar coda, all in E minor Duetto II BWV 803 The second duet in F major BWV 803 is a fugue written in the form of a da capo aria, in the form ABA. The first section has 37 bars and the second 75 bars, so that with repeats there are 149 bars. There is a sharp contrast between the two sections, which has suggested might have been 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. Section B is divided symmetrically into segments of 31, 13 and 31 bars. The