Our hypothesis is that in Paraguay’s Jesuit missions the Indian authorities, whose language was Guaraní, identified the medieval political concept of love with their own conceptions of ownership and possession of others, while the Jesuits thought they had found the exact equivalent of their conceptions of love in the Guaraní verb ayhu. We show that this was a case of ‘double mistaken identity’, but that it was nonetheless productive in that it entrenched, for a very long time, a certain conception of asymmetrical mutual love in Guaraní-speaking societies. To conduct our demonstration we reread recent works in Tupí-Guaraní prehistory and anthropology and analysed documents written in Guaraní by mission Indian authorities between 1750 and 1810, which as a team we did the palaeography, transliteration, and translation for an open-access database, available at www.langas.cnrs.fr.