Three-Part Inventions Bachs Three-Part Inventions, BWV 787-801 (also known as Sinfonias) were composed in Köthen, Germany around the year 1720 for harpsichord. Each work is characterized by the contrapuntal working of a single melodic line. The fifteen short pieces cover eight major and seven minor keys. Bach included with the collection of the Two and Three-Part Inventions these instructions to students of music: Forthright instruction, wherewith lovers of the clavier, especially those desirous of learning, are shown in a clear way not only 1) to learn to play two voices clearly, but also after further progress 2) to deal correctly and well with three obbligato parts, moreover at the same time to obtain not only good ideas, but also to carry them out well, but most of all to achieve a cantabile style of playing, and thereby to acquire a strong foretaste of composition. Ralph Sauer has newly arranged these fifteen small masterpieces for three trombones in one single collection. which is appropriate for advanced performers.