Bach's cadenza.

THE stretch of music at the end of the Fifth Brandenburg Concerto of Johann Sebastian Bach is probably the first fully written-out (rather than improvised) cadenza in the history of music and, over 275 years later, still the most exciting. The harpsichordist (or pianist) is rattling along like a good soldier when suddenly he begins to take off. Up and down the scale, the harmonies subtly changing. A flute and a violin are still there, but their role diminishes and ... the keyboard player is on his own! Sixty-five bars of music, with gradual changes of harmony and speed--demisemiquaver, the musicologists call a note that sounds for one thirty-secondth of a full beat--but wait! Then Bach changes the rhythm into thirds, so in the same mini-second you get not ta-da tada ta-da, but ta-da-da ta-da-da ta-da-da. And then, the rest of the orchestra comes back in and, in humble deference to the titanic passage just performed on the keyboard, does a routine ending, just nine measures and the movement is over. This is the beauty for which I confess nothing less than a passion.

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