In this article, moving from being to becoming, we construe the ‘self’ as a dynamic process rather than as a static entity. To this end we draw on dialectics and Bayesian accounts of cognition. The former allows us to holistically consider the ‘self’ as the interplay between internalization and externalization and the latter to operationalize our suggestion formally. Internalization is considered here as the co-construction of bodily hierarchical models of the (social) world and the organism, while externalization is taken as the collective transformation of the world. We do not consider these processes as sequentially linked, but rather as a dialectic between the collective and the individual. This leads us to the suggestion of the self as a historical product of dialectical attunement across multiple time scales, from species evolution and culture to individual development and everyday learning. Subsequently, we describe concrete means for empirically testing our proposal in the form of two-person psychophysiology and multi-level analyses of intersubjectivity. Taken together, we suggest that a fine-grained analysis of social interaction might allow us to reconsider the ‘self’ beyond the static individual, i.e. how it emerges and manifests itself in social relations. Such an approach, we believe, could be relevant in multiple fields, from ethics and psychiatry to pedagogy and artificial intelligence.