strong preference for Mattheson's "natural" melody over Bach's "artful" counterpoint. Through his friend Mizler and his Leipzig printers Krügner and Breitkopf, also printers for Mattheson, like others Bach would have had advance knowledge of the content of Mattheson's treatise. Concerning counterpoint, Mattheson wrote: Whatever Bach's personal reaction, the contrapuntal writing of Clavier-Übung III provided a musical response to Scheibe's criticisms and Mattheson's call to organists. Mizler's statement, cited above, that the qualities of Clavier-Übung III provided a "powerful refutation of those who have ventured to criticize the music of the Court Composer" was a verbal response to their criticisms. Nevertheless, most commentators agree that the main inspiration for Bach's monumental opus was musical, namely musical works like the Fiori musicali of Girolamo Frescobaldi, for which Bach had a special fondness, having acquired his own personal copy in Weimar in 1714. Textual and musical plan The number of chorale preludes in Clavier-Übung III, twenty-one, coincides with the number of movements in French organ masses. The Mass and Catechism settings correspond to the schedule of Sunday worship in Leipzig, the morning mass and afternoon catechism. In contemporary hymn books, the Lutheran Mass comprising the troped German Kyrie and German Gloria fell under the heading of the Holy Trinity. The organist and music theorist Jakob Adlung recorded in 1758 the custom of church organists playing the two Sunday hymns "Allein Gott in der Höh sei Ehr" and "Wir glauben all an einen Gott"' in different keys: Bach uses three of the six tonalities between E and B mentioned for "Allein Gott". The organ had no role in the catechism examination, a series of questions and answers on the faith, so the presence of these hymns was probably a personal devotional statement of Bach. However, Luther's Shorter Catechism (see illustration) centres on the Ten Commandments, the Creed, the Lord's Prayer, Baptism, Office of the Keys and Confession, and the Eucharist, the exact subjects of Luther's own six catechism chorales. In Bach's part of Germany, these catechism hymns were sung at school assemblies on weekdays, with the Kyrie and Gloria on Sundays. Luther's hymn book contains all six of the chorales. However, it is more likely that Bach used these hymns, some of them Gregorian in origin, as a tribute to the main precepts of Lutheranism during the special bicentenary year of Luther's 1539 sermon in the Thomaskirche, Leipzig. The main texts for Lutherans were