"In medieval times, the Church used to sell 'indulgences' for money. This amounted to paying for some number of days' remission from purgatory, and the Church literally (and with breathtaking presumption) issued signed certificates specifying the number of days off that had been purchased. . . . And of all its money-making rip-offs, the selling of indulgences must surely rank among the greatest con tricks in history. . . ."