This concerto, composed during Johann Sebastian Bach’s Cöthen period, is thought to be based on a lost violin concerto. It is clear from the manuscript notation that the concerto was composed for the two manuals of the harpsichord, but it is frequently performed on the single keyboard of the modern piano. The piece is composed in three movements; the first one was later used by Bach as an organ prelude, and the slow movement became the first chorus of his Cantata No. 146, “Wir müssen durch viel Trübsal.”
Like most of Bach’s instrumental concertos, this work employs the Italian ritornello form. The ritornello of the first movement is a driving six-bar unison theme whose opening five notes form the foundation for the majority of the movement. The theme’s power stems from its ever-expanding leaps and its emphatic closing cadence. Most of the soloist’s passages are derived from this theme, but Bach later introduces a chromatic, toccata-like secondary theme for effect. The ritornello immediately gives way to a carefully mapped progression through the neighboring keys, using the dominant minor, the relative major, the relative major of the dominant minor, and so forth. The soloist leads the concerto through sections of contrapuntal and harmonic exploration, interspersed with several varied restatements of the ritornello by the strings. Following an elaborate cadenza by the soloist, the first movement closes with a unison restatement of the ritornello. The slow second movement is in G minor, which is unusual in that most of Bach’s concertos and sonatas that begin in a minor key have a second movement in a major key, and vice-versa. Like Bach’s two violin concertos, the movement is built on a foundation of a solemn basso ostinato which also serves as the ritornello. The movement’s structure is symmetrical, with the first half progressing from G minor to C minor, and then to a B flat major cadence; the progression then retraces its steps, through C minor and again back to G minor. Similarly, the opening and closing statements of the ritornello are both in unison. Throughout the piece, the soloist weaves an increasingly florid melody over the ground bass, adding a lyrical quality to the somber character of the movement. The Allegro finale movement is constructed in a similar manner to the opening movement. In 3/4 time, its opening 12-bar ritornello begins with a downward scale and has a recurring rhythmic figure consisting of two sixteenth notes and an eighth note. In parts of the ritornello, the melody is traded between the bass and treble. The first solo section is a toccata-like figure. The final statement of the ritornello is preceded by a short but elaborate cadenza, as in the first movement.