the second movement of bwv 1017 in common time is a "concerto allegro" according to eppstein's classification. 109 bars long, has described it as "a mammoth compendium of musical ideas all somehow integrated into one of the most intensive fugal movements bach ever wrote." the movement is built on a ritornello which contains both a fugue subject and a countersubject. new material is also introduced in a brief two bar interlude a third of the way through the movement. the ritornello, or parts of it, recurs ten times in the movement, which it also concludes. the fugue subject is heard in c minor and g minor, and their relative major keys, e major and b major; further complexity is added by reprises starting in the middle of a bar. musical material from the ritornello and interlude is developed extensively in the many intervening episodes.