inspired by the five-part textures of Grigny, with two parts in each manual and the fifth in the pedal. Commentators have taken Clavier-Übung III to be a summation of Bach's technique in writing for the organ, and at the same time a personal religious statement. As in his other later works, Bach's musical language has an otherworldly quality, whether modal or conventional. Compositions apparently written in major keys, such as the trio sonatas BWV 674 or 677, can nevertheless have an ambiguous key. Bach composed in all known musical forms: fugue, canon, paraphrase, cantus firmus, ritornello, development of motifs and various forms of counterpoint. There are five polyphonic stile antico compositions (BWV 669–671, 686 and the first section of 552/ii), showing the influence of Palestrina and his followers, Fux, Caldara and Zelenka. Bach, however, even if he employs the long note values of the stile antico, goes beyond the original model, as for example in BWV 671. describes one aim of Clavier-Übung III as being to provide an idealized programme for an organ recital. Such recitals were described later by Bach's biographer Johann Nikolaus Forkel: The musical plan of Clavier-Übung III conforms to this pattern of a collection of chorale preludes and chamber-like works framed by a free prelude and fugue for organum plenum. Numerological significance has given an analysis of the numerology of Clavier-Übung III. According to Wolff there is a cyclic order. The opening prelude and fugue frame three groups of pieces: the nine chorale preludes based on the kyrie and gloria of the Lutheran mass; the six pairs of chorale preludes on the Lutheran catechism; and the four duets. Each group has its own internal structure. The first group is made up of three groups of three. The first three chorales on the kyrie in the stile antico hark back to the polyphonic masses of Palestrina, with increasingly complex textures. The next group consists of three short versets on the kyrie that have progressive time signatures , , and . In the third group of three trio sonatas on the German gloria, two manualiter settings frame a trio for two manuals and pedal with a regular progression of keys, F major, G major and A major. Each pair of catechism chorales has a setting for two manuals and pedal followed by a smaller scale manualiter fugal chorale. The group of 12 catechism chorales is further broken up