first subject of section A is heard again in canon in the minor key. The character of the first subject undergoes a complete transformation, from bright and effortless simplicity to dark and strained complexity: the strettos in the first subject produce unusual augmented triads; and a new chromatic countersubject emerges in the central 13-bar segment (which begins in bar 69, the fifth bar below). The musical structure of Section A is as follows: bars 1–4: (first) subject in right hand, F major bars 5–8: subject in left hand, semiquaver countersubject in right hand, C major bars 9–16: episode on material from countersubject bars 17–20: subject in right hand, countersubject in left hand, C major bars 21–28: episode on material from countersubject bars 29–32: subject in left hand, F major bars 33–37: coda The musical structure of Section B is as follows: bars 38–45: second subject (in two 4 bar segments) in canon at the fifth, led by right hand bars 46–52: first subject in canon at the fifth, led by the right hand, D minor bars 53–60: second subject in canon at the fifth, led by left hand bars 61–68: first subject in canon at the fifth, led by left hand, A minor bars 69–81: first subject in left hand with chromatic countersubject in right hand (5 bars), inverted first subject in right hand with inverted chromatic countersubject in rleft hand (5 bars), semiquaver passagework (3 bars) bars 82–89: second subject, in canon at the fifth, led by left hand bars 90–96: first subject in canon at the fifth, led by left hand, F minor bars 97–104: second subject in canon at the fifth, led by right hand bars 105–112: first subject in canon at the fifth, led by right hand, C minor Duetto III BWV 804 The third duet BWV 804 in G major, 39 bars long, is the simplest of the four duetti. Light and dance-like, it is the closest in form to Bach's Two Part Inventions, of which it most closely resembles the last, No.15 BWV 786. The bass accompaniment in detached quavers of the subject does not appear in the upper part and is not developed. With very little modulation or chromaticism, the novelty of BWV 804 lies in the development of the semiquaver passagework. Apart from a contrasting middle section in E minor, the tonality throughout is resolutely that of G major. The use of