Michel de Certeau and his book, The Possession at Loudun, are the central subjects of this essay, in which the question of belief is addressed. Who can you believe and how? Is belief engendered by a person’s speech, facial expression, or gesture? The revolt of the nuns in Loudun, following the Plague, had, for Certeau, a theatrical dimension as if they were acting out an unexpressed failure of communication between the clergy and the people. Their mass dementia represented a cataclysmic change in social relations. Certeau found two people who spoke with a convincing clarity: Urbain Grandier from his prison cell and Joseph Surin, Jesuit, poet, and exorcist.