Progression Improvisation and/or Development

Among the various kinds of improvisation, one of the most commonly employed is to base one’s innovations and creative input on the harmonic progression, that is, chord changes of a given song. In its more popular usage, this is what instrumentalists do quite often in popular music. In rock songs we hear it as the instrumental part when someone “takes it” between sung verses. In classical music we hear the same basic concept akin to variations on a theme, the difference being that as the progression repeats it is not always with a variation of the melody. Bach’s famous Chaconne in D minor (from the Partita in D minor for violin, BWV 1004) is the most famous example, probably, of a piece built on the repetition of a progression, as is his Passacaglia in C minor (Passacaglia and Fugue in C minor BWV 582) that is followed by a fugue. But the difference between that Chaconne and that Passacaglia is that the latter has a recognizable melody that begins in the bass, and is heard in every variation. Afterward, a fugue is based on the first half of that melody, combined to a second melodic line, making that fugue a “double fugue,” and an unusual double fugue at that because the two “subjects” are played together throughout instead of one following the other with what seems like a separate fugal section. By presenting both pieces here I mean to show that a comparison between the forms demonstrates the difference between developing on the basis of a harmonic progression (the Chaconne) and, essentially, variations on a theme (the Passacaglia).