the second movement of bwv 1019 is a largo in e minor in triple time. a brief movement of only 21 bars in length, it has the tonal purpose of mediating between the keys of g major and e minor of the first and third movements. with the opening allegro, it is one of the two movements present in every version of the sonata. the scoring, however, evolved as bach added a third "middle" voice to the harpsichord part in later versions. this change results in the harpsichord part itself evolving within the piece as the middle voice enters: the texture of the accompaniment is gradually transformed from a simple continuo to a fully realised three-part accompaniment.