The ontological turn is one of the most debated issues in contemporary anthropology, but what it means for anthropology to become ontological is rarely made clear. Bruno Latour’s suggestion that anthropology should revolve around “modes of existence” is arguably the most robust proposal to date, but the connection between modes of existence and properly anthropological concerns remains obscure. This paper argues that William James is a key figure for getting a better understanding of what ontology and modes of existence mean, (...) and that in particular “The Perception of Reality” – chapter XXI of the second volume of the Principles of Psychology – offers many possibilities for linking a framework centered on human being-in-the-world, such as anthropology, with properly metaphysical concerns. In this paper, the content of “The Perception of Reality” is summarized, and James’s proposal to ground modes of existence on belief is discussed, to show how, once we are clear about what we mean by “ontology,” anthropology can (and should) engage in metaphysical debates in order to make its stakes explicit. The conclusion suggests that James’s grounding of modes of existence on individual belief can compensate for ontological anthropology’s tendency to erase the internal differences of a collective in order to speak of a supposedly unified and homogeneous “cosmology.”. (shrink)