Voltaire's works, especially his private letters, frequently urge the reader: "", or "crush the infamous". The phrase refers to contemporaneous abuses of power by royal and religious authorities, and the superstition and intolerance fomented by the clergy. He had seen and felt these effects in his own exiles, the burnings of his books and those of many others, and in the atrocious persecution of Jean Calas and François-Jean de la Barre. He stated in one of his most famous quotes that "Superstition sets the whole world in flames; philosophy quenches them."