How can they be put to the test in the face of the unanswered question? Consider: How much is actual prediction of the “wave form” (as Muad’Dib referred to his vision-image) and how much is the prophet shaping the future to fit the prophecy? What of the harmonics inherent in the act of prophecy? Does the prophet see the future or does he see a line of weakness, a fault or cleavage that he may shatter with words or decisions as a diamond-cutter shatters his gem with a blow of a knife?

Frank Herbert, Dune