This article is an ethnographic essay on the notion of an 'ontological turn', taken here in its literal sense of ontological change. It explores a specific sociocosmological transformation – one resulting from the conversion of an Amazonian people, the Wari', to Christianity – via the concept of ontology. The central question here concerns the relationship between an Amazonian animist/perspectivist ontology and the naturalism characteristic of Christian-Western thought. Through a critical reading of the notion of ontological change advanced by Descola (2013) in Beyond Nature and Culture, the article aims to show that the transformation experienced by the Wari' with the arrival of Christianity can be described neither as a linear transition between ontologies, nor as the result of the foregrounding of conceptions or kinds of relationship previously found in an encompassed form. The separation between humans and animals, and the constitution of an inner self typical of Christian naturalism, are becoming gradually absorbed into the Wari' world now but were non-existent and inconceivable in their traditional universe. An examination of the translation choices made by the Evangelical missionaries from the New Tribes Mission and the apprehension of these ideas by the Wari' suggests a complex and non-linear transition between the two ontologies.