Contrapunctus IX, “alla duodecima,” from The Art of the Fugue, BWV 1080
The Art of the Fugue may well be Bach’s seminal work and contains 14 fugues and four canons, all in D-minor, and arranged in increasing difficulty. … Instead of calling them “counterpoint(s),” Bach preferred the Latin word “Contrapunctus.” Number IX (9) is a study of turning that simple subject into a new derivation and into a double fugue (two themes treated as a fugue at the interval of a twelfth, thus the subtitle “alla duodecima”)…