Today we call it “plagiarism,” but back in the heyday of baroque music, in the late 17th to early 18th centuries, reworking another composer’s music — or your own — was considered an indication of respect. Bach did it copiously from, for instance, the music of Telemann, Vivaldi, Lutheran hymn melodies and — most of all — himself. On Sunday at the National Presbyterian Church, under the auspices of the Washington Bach Consort, organist/harpsichordists J. Reilly Lewis (the WBC’s music director) and Scott Dettra (the Washington National Cathedral’s organist) collaborated on a beautifully conceived program that focused on Bach’s music for organ (the “Choral Preludes”) and for harpsichord, with roots in numerous sources.
Chorales based on Lutheran hymns or folk melodies, sung here by a quartet of WBC singers, were followed by organ preludes on the same melodies. A concerto for two harpsichords began life as a piece either for two violins or for violin and oboe (the chronology being uncertain), and there were several pieces that Bach lifted and reworked from Telemann and a number of lesser composers of the time. What gave the program such coherence was the grouping of works that shared a common spirit (exuberance, reflection, hope and the like) and a common tonality. A quintet of strings was the “orchestra” for the harpsichord concertos.