In the mid-sixteenth century, Jesuit missionaries working in what is now Brazil were struck by what they called the inconstancy of the people they met, the indigenous Tupi-speaking tribes of the Atlantic coast. Though the Indians appeared eager to receive the Gospel, they also had a tendency to forget the missionaries’ lessons and “revert” to their natural state of war, cannibalism, and polygamy. This peculiar mixture of acceptance and rejection, compulsion and forgetfulness was incorrectly understood by the priests as a sign of the natives’ incapacity to believe in anything durably. In this pamphlet, world-renowned Brazilian anthropologist Eduardo Viveiros de Castro situates the Jesuit missionaries’ accounts of the Tupi people in historical perspective, and in the process draws out some startling and insightful implications of their perceived inconstancy in relation to anthropological debates on culture and religion.