subject, based on the second line of the cantus firmus, starts in the alto part on the last quaver of bar 7: The two subjects and the semiquaver motif are combined from bar 16 to the close. Examples of musical iconography include the minor triad in the opening subject and the descending scales in the first half of bar 16—references to the Trinity and the heavenly host. Chorale preludes BWV 678–689 (Luther's catechism chorales) Careful examination of the original manuscript has shown that the large scale chorale preludes with pedal, including those on the six catechism hymns, were the first to be engraved. The smaller manualiter settings of the catechism hymns and the four duets were added later in the remaining spaces, with the first five catechism hymns set as three-part fughettas and the last as a longer four-part fugue. It is possible that Bach, in order to increase the accessibility of the collection, conceived these additions as pieces that could be played on domestic keyboard instruments. Even for a single keyboard, however, they present difficulties: in the preface to his own collection of chorale preludes published in 1750, the organist and composer Georg Andreas Sorge wrote that, "the preludes on the catechism chorales of Herr Capellmeister Bach in Leipzig are examples of this kind of keyboard piece that deserve the great renown that they enjoy," adding that "works such as these are so difficult as to be all but unusable to young beginners and others who lack the considerable proficiency they require." The Ten Commandments BWV 678, 679BWV 678 Dies sind die heil'gen zehn Gebot (These are the holy Ten Commandments) Below is the text of the first verse of Luther's hymn with the English translation by Charles Sanford Terry: The prelude is in the mixolydian mode of G, ending on a plagal cadence in G minor. The ritornello is in the upper parts and bass on the upper manual and pedal, with the cantus firmus in canon at the octave on the lower manual. There are ritornello episodes and five entries of the Cantus firmus, yielding the number of commandments. The distribution of parts, two parts in each keyboard and one in the pedal is similar to that of the de Grigny Livre d'Orgue, although Bach makes much greater technical demands on the right hand part. Commentators have seen the canon as representing order, with the pun on