the opening movement is a concerto allegro in g major and common time. this already sets the sonata apart from the previous sonatas, which like the sonatas da chiesa of corelli start with slow movements: bwv 1019, like the instrumental concertos of bach, begins with a fast movement. symmetrical in structure and written in strict da capo form, its opening 21 bar ritornello is scored as a tutti section for all three parts. the toccata-like semiquaver theme descending in the violin is matched by a rising quaver countersubject in the upper keyboard, with a rhythmic quasi-continuo in the bass line. the upper voices are written in invertible counterpoint in the ritornello, with the musical material alternating every two or four bars. the semiquavers continue unabated like a moto perpetuo throughout the ritornello, passing from one voice to another. after the first eight bars, when the main theme is heard twice, there is an eight-bar interlude when the violin and upper keyboard play in counterpoint, alternating between semiquaver motifs derived from the main theme and a syncopated countersubject.