At the same time as, in Paris, Lucien Lévy-Bruhl experimented with the concept of “participation,” in Harvard, William James undertook a parallel trajectory by taking recourse to the notion of “the vague.” For him, vagueness described the fact that reality is richer than any and all conceptualizations. In light of the ethnographic material provided by contemporary developments in ethnography, this paper mobilizes James’ concept of the vague by reference to Lévy-Bruhl’s participation in order to develop instruments for capturing ethnographically the complexities of entanglement and emergence in human sociality. The paper concludes that indeterminacy and underdetermination are doors of entanglement as they both limit and make possible the constitution of entities in sociality.