Like most of Bach’s large-scale organ works, the epic Passacaglia and Fugue in C minor was composed when playing the organ was still part of his job description, which stopped being the case in 1717 when he turned 32. The passacaglia form itself had been around more than a century, originating as a chord pattern rather like a Renaissance 12-bar blues. By Bach’s day the word meant a series of variations over a repeating bass figure, which Bach obligingly introduces by itself so there can be no missing it. The bass line changes and migrates into the upper voices, which has led some scholars to argue that the piece is not a passacaglia, but something else, but in fact terms like “passacaglia” or “chaconne” never had rigid definitions, and on this one occasion when he called something a passacaglia, Bach doubtless knew what he meant. His passacaglia is followed by a double fugue in which the first subject is very recognizably the first part of the ground bass, and the second subject is, not so recognizably, derived from the second part.