Complexity, as it is usually understood, is based on non-linear but reductive Newtonian relations. This formulation of complexity limits its value to social theorising, including the theorising of human practices. However, if complexity is understood to be based on non-linear but complex relations, for which Deweyan trans-actions can stand as an exemplar, it can provide an onto-epistemological ... [Show full abstract] framework for the consideration of living systems, including those of practice. This framework allows for a non-reductive conceptualisation of practice that encompasses both individual and social aspects of human functioning. In this chapter, it is used to focus on the workings of the co-present group, that nexus of complex relations where meaning is produced from affective processing and where the social, including practice, is created and individuals learn.