An examination of the role of the anthropologist as an expert of the court in a case of early (“child”) marriage among a Roma migrant family in the UK leads to a reflection on the uses of anthropological knowledge in the public sphere (a courtroom) and the simplifications that can be generated. Drawing on Emmanuel Todd’s idea of the endogamous communitarian family as the most conformist (intégrateur) social formation known in the history of humanity, the paper explores questions around tradition, autonomy, and the possibilities of social change. At the same time, the presentation joins an increasingly rich and diverse academic conversation on the complex relationship between academic and legalistic reasoning.