The Art of Fugue or The Art of the Fugue (original German: Die Kunst er Fuge), BWV 1080, is an incomplete masterpiece by Johann Sebastian Bach (1685-1750). The work was probably started in the beginning of the 1740s, if not earlier. The first known surviving version, which contained 12 fugues and 2 canons, was copied by the composer in 1745. This manuscript has a slightly different title, added afterwards by his son-in-law Johann Christoph Altnickol: Die Kunst der Fuga. Bach's second version was published in 1751 after his death. It contains 14 fugues and 4 canons. "The governing idea of the work," as the eminent Bach specialist Christoph Wolff put it, is "an exploration in depth of the contrapuntal possibilities inherent in a single musical subject."