Orchestration: strings, basso continuo, solo violin, and solo oboe. First Los Angeles Philharmonic performance: October 11, 1973, with violinist Tze-Koong Wang and oboist David Weiss, Sidney Harth conducting.

Like many of the Bach concerti in the repertoire, the C-minor Concerto for violin and oboe, adapted from a concerto for two harpsichords, is a very educated guess about what Bach originally wrote.

Most of Bach’s concerti are believed to have been written between 1717 and 1723 when, as Kapellmeister at the princely court of Anhalt-Cöthen, he led a small band of very accomplished players. When Bach went to Leipzig to become Cantor of the Thomaskirche in 1723, his professional and personal life changed drastically. Cöthen, a Calvinist establishment, had no use for elaborate church music, and Bach had concentrated on composing for orchestra. In Leipzig Bach was in charge of music for three churches and had little need to write concertos and little opportunity to perform them. On the other hand, three of his sons were now musicians in training old enough to cut their teeth on serious fare. In 1723, Wilhelm Friedemann was 13, Carl Philipp Emanuel nine, and Johann Gottfried Bernhard eight. There were also daughters who, while not destined for musical professions, were undoubtedly educated in music (Bach’s second wife, Anna Magdalena, had been a professional singer). In addition to a houseful of kids, Bach also owned a houseful of harpsichords (he left seven of them when he died), and enough string instruments to outfit a small orchestra, so it made sense to rearrange his Cöthen concerti for harpsichords and strings.

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Eighteenth-century composers reused their music far more than we would be comfortable with now. In an era when little music was published and none was recorded, composers who changed situations often faced the prospect of having perfectly good music get moldy in closets because they had landed in some place where there was no audience for the composition’s genre. So just as Handel cannibalized his German passion music and Italian oratorios and cantatas when he got to England, where there was no market for the originals, Bach, who changed jobs a half-dozen times, frequently reworked his music in different forms, giving the avid Bach listener much occasion for déjà vu. His concertos are a prime playing field for the Bach Concordance Game.

If Bach’s concerti for one, two, three, or four harpsichords are transcriptions, how do we know what their original form was? Bach left an enormous amount of evidence about his technique for arranging music. In some cases, the original versions have survived, including works by other composers as well as by Bach. Vivaldi was obviously a favorite; there are no fewer than ten extant Bach arrangements of Vivaldi concertos. In other instances, Bach’s manuscript of the harpsichord version survives, with erasures and changes still visible. Some movements of harpsichord concerti also exist as instrumental movements in cantatas.

These sources show that in adapting a concerto for some other instrument Bach would typically give the solo part to the harpsichordist’s right hand, leaving the range and key of the original solo part intact, and add a left-hand part. The result is that the range (and the key) of the right-hand almost always resembles the way Bach wrote for a particular instrument in his other works. To an experienced eye the identity of original instrument – usually violin, oboe, or oboe d’amore – is fairly obvious. Even among musicologists, who are a pretty contentious lot, there is widespread agreement about the original form of most of Bach’s concerti. The two solo parts of the C-minor Concerto exactly fit the range of the violin and the oboe. The arpeggiated figurations of the violin part are absent in the oboe part, since such passagework is not idiomatic for oboe.

In the slow movement, the two instruments trade pieces of the same long-lined melody while the accompanying strings are relegated to an almost unnoticed background. The result is a timeless tenderness not so different in effect from the slow movement of Mozart’s Third Violin Concerto.

Lawyer and lutenist Howard Posner has also annotated programs for the Los Angeles Baroque Orchestra and for the Coleman Chamber Concerts. This summer his notes will appear in the program of the Salzburg Festival.