From the biographical sketch, by Professor Peter Schickele.
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This most mini musical life has been divided into three creative periods: the Initial Plunge, the Soused Period, and Contrition. The middle period was by far the longest of the three, and was characterized by a multiplicity of contrapuntal lines and a greater richness of harmony due to almost constant double vision. It was during this period that he emulated (i.e., stole from) the music of Haydn and Mozart, but his pathetic attempts to be au courant were no more successful than his pathetic attempts to be passé had been during the Initial Plunge; having to cope with the problems that accompany immense popularity was something P.D.Q. Bach managed to avoid. It has been said that the only original places in his music are those places where he forgot what he was stealing. And, since his memory was even shorter than his sightedness, he was in point of fact one of the most original composers ever to stumble along the musical pike.