The enigmatic character of became apparent as early as in its first edition, printed more than a year after the composer’s death. Carl Philipp Emanuel Bach, who published both the first and the second editions, raised several unsolved questions regarding this opus. Anatoly P Milka presents a consistent and coherent solution to the unresolved questions about the history, structure and appearance of J.S. Bach’s , opening new perspectives for further exploration of this musical masterpiece. Milka challenges the present scholarly consensus that there exist two different versions of (the Autograph and the Original Edition) and argues that Bach had considered four versions, of which only two are apparent and have been discussed so far. Only Bach’s illness and death prevented him from fulfilling his plan and publishing a fourth, conclusive version of his opus.