Improvisation in the Brandenburg Concertos

We love the Brandenburg Concertos. They show Bach at his most vibrant, his most colorful, and they’re so unusual and challenging that it wasn’t until 1850 that these concertos really became popular. Like other collections of Baroque or Classical music, they’re grouped in a set of six. Unlike most other collections, these six works are vastly different from one another. Bach wrote them as individual pieces and only retroactively compiled them into a collection. They have wildly different instrumentations, different sequences of movements, and different expressive characters. And, unlike his Art of the Fugue, Goldberg Variations, or even The Well-Tempered Clavier, they aren’t an in-depth study of one technique or theme or temperament. Instead they cover nearly the entire gamut of what was possible in Baroque concertos—they push the concerto to its limits.

Bach is famous for his meticulously worked-out music. The Brandenburgs are no exception, so they make an interesting example of a sometimes-overlooked feature of Baroque music: how incredibly improvisational it is. When we think of improvisation, we tend to think of a cadenza, the moment in a concerto when the orchestra drops out and the soloist plays a virtuosic fantasia. Two of the Brandenburgs have cadenzas—there’s a shorter one in the Third Concerto over a held chord and a longer one in the Fifth Concerto.

However, improvisation is also at the foundation of Baroque music. A composer like Bach would write the bassline for various instruments (in the Brandenburgs they’re cello and bass) and expect a harmony instrument (like the harpsichord) to extemporize its part based on the chords suggested by the bassline. Called basso continuo, this practice was common throughout the Baroque period and is one of the defining features of Baroque music.

So what did all this improvisation sound like during the Baroque period? We can make educated guesses about exactly how the music was performed but we don’t know for sure. There are various treatises that give guidelines but it can be difficult to tell when the author is describing current practice and when the author is stating their opinion. For instance, many treatises warn against overly flashy basso continuo playing. Johann Quantz wrote in 1752, “Those that consist in a continual series of swift notes or quick passages, though ever so much admired by some, in general are not so pleasing as those of the more simple kind…” But how common was “swift note” continuo versus a simpler, chordal style?

There are some clues in other treatises. J.F. Daube, in a theory manual from 1756, divides continuo styles into simple, natural, and complex. The simple style was for solos, trios, arias, and concertos. The natural style was mainly for recitative, and the complex style was for plain pieces that could use some additional imitation or an extra voice. Apparently Bach was especially good at the complex style. Daube made a point of praising him:

“The most excellent Bach had perfected this third [complex] method to the highest degree. Through him the upper voice came to life… He knew how to imitate it with either the right or left hand, or how to use a counter theme unexpectedly so that the listener would have sworn that it had been written that way… Generally his accompaniment was always like a concertante voice, which had been worked out with the greatest diligence, and which displaced the upper voice [in interest]. This right was then extended to the bass without taking away from the upper voice. Enough! He who has not heard [Bach] has missed much.”
(Translated by Barbara K. Wallace)

The complex style of continuo, fascinating as it must have been, was out of style by the time Daube wrote about Bach (six years after the composer’s death), and remains out of style today, so we’ll never know exactly what it sounded like. But Daube’s description shows just how much a continuo player could transform a piece.

The Brandenburgs, in contrast, fall into the simple style of continuo playing since they have many independent parts already written out. The basso continuo supports and complements the upper parts, providing an important foundation for the music.

The music contains clues that a continuo player can use to create their part. For instance, harpsichordist Kenneth Weiss describes his general approach to continuo playing, “I become aware of each instrumental part and… I then take into account rhythmic, harmonic, dynamic, melodic, and stylistic elements to be brought out, underlined, or embellished upon.” In the Third Concerto, you can hear how the harpsichord fits seamlessly into the texture.

Baroque keyboard players like Bach didn’t just create continuo parts, however. They also frequently improvised solo filler music like preludes, interludes, and postludes. They tended to play a functional role in keeping the music going, often introducing and supporting melody instruments. In the Brandenburgs, Bach takes harpsichord improvisation one step further and writes an extended cadenza in the Fifth Concerto. At that time, harpsichords did not have solo parts in concertos. Ever. To introduce this new role for the harpsichord, Bach plays with the audience’s expectations by sneaking in the harpsichord’s solos—first a short one, then a longer one, and finally an extended cadenza that takes up nearly a third of the movement. While the cadenza is not technically improvised (it’s fully written out in the score), it is a telling look at Bach’s improvisational style. Given that the cadenza is the climax of the movement, he may have written it out to underline its importance.