successive pieces. What has called the "new, transcendental quality" of these chorale fughettas is due in part to the modal writing. The cantus firmus in the phrygian mode of E is ill-suited to the standard methods of counterpoint, since entries of the subject in the dominant are precluded by the mode. This compositional problem, exacerbated by the choice of notes on which the pieces start and finish, was solved by Bach by having other keys as the dominating keys in each fughetta. This was a departure from established conventions for counterpoint in the phrygian mode, dating back to the mid-16th century ricercar from the time of Palestrina. As Bach's pupil Johann Kirnberger later remarked in 1771, "the great man departs from the rule in order to sustain good part-writing."BWV 672 Kyrie, Gott Vater (Kyrie, O God, Eternal Father) BWV 672 is a fughetta for four voices, 32 bars long. Although the movement starts in G major, the predominant tonal centre is A minor. The subject in dotted minims (G–A–B) and the quaver countersubject are derived from the first line of the cantus firmus, which also provides material for several cadences and a later descending quaver figure (bar 8 below). Some of the sequential writing resembles that of the B major fugue BWV 890/2 in the second book of The Well-Tempered Clavier. Smoothness and mellifluousness result from what has called the "liquefying effect" of the simple time signature of ; from the use of parallel thirds in the doubling of subject and countersubject; from the clear tonalities of the four-part writing, progressing from G major to A minor, D minor, A minor and at the close E major; and from the softening effect of the occasional chromaticism, no longer dramatic as in the conclusion of the previous chorale prelude BWV 671.BWV 673 Christe, aller Welt Trost (Christ, Comfort of all the world) BWV 673 is a fughetta for four voices, 30 bars long, in compound time. It has been described by as "a movement of immense subtlety". The subject, three and a half bars long, is derived from the first line of the cantus firmus. The semiquaver scale motif in bar 4 is also related and is much developed throughout the piece. The countersubject, which is taken from the subject itself, uses the same syncopated leaping motif as the earlier Jesus Christus unser Heiland BWV 626 from the Orgelbüchlein, similar to