Abstract
How can a Christian political society be founded when the wood of the cross is, in the words of Jacques Dalarun, " the framework and thorn in the side of medieval societies " ? The lecture poses this question, taking as its starting point the testing of Christianity by Jesuit missionaries in 17th-centuryJapan . Above all, however, the aim is to propose, based on Grandmont's political experience, a grammar of political experimentation that can be broken down into eight basic rules. All political experimentation is an existential experience (1), and the link it establishes is one of repetition, not foundation (2). To sharpen the sense of community (3), consensus is built by isolating the pars minor (4) : this is the bond of division (5) that characterizes medieval experimentation. But for institutions to last (6), we need to take into account both the reversibility of political experiments (7) and their ability to change scale in order to constitute a plausible utopia (8). It is on this notion of scalability, thought from Anna Tsing's proposals, that the lecture provisionally ends, displacing the anthropologist's interrogation of the contemporary on the " bushy edges of the ruins of capitalism " to the medieval dilemma faced with the ruins of the Roman Empire.