The premise of Daniel Stern’s theory is the notion that the infant possesses the psychic capacity to differentiate a subjective sense of self from the other. Furthermore, this self-differentiating infant is a social creature whose relationships serve a central function in distinguishing both a sense of self and other. In essence, Stern argues that the infant is pre-wired to be both relatable and self-differentiated. This poses a challenge to Margaret Mahler’s conception of the infant as existing in a psychologically fused state with the mother—only arriving at a sense of self after successfully emerging from symbiotic union with the mother, and subsequently proceeding through discrete phases that further facilitate the self-individuation process.
Stern accounts for the infant’s sense of a core self by referring to a large body of developmental research that points to the existence of certain self-invariants that function as a framework for providing consistent ways of organizing the world, and more importantly, one’s position and agency within the world. Stern believes that the infant has certain nascent ego capacities that facilitate its ability to adapt to reality (e.g. by playing an active role in relationship formation). Stern disputes the ego psychological view of the infant as a mere undifferentiated, psychologically embedded entity, reliant on the mother as an “auxiliary ego” for mediating the world around him. It should be noted that while Stern promotes the notion of a self-differentiated infant, he does not dismiss the central role that the mother plays as a self-regulating other whose patterns of interaction with the infant become internalized and go on to become the enduring, relational prototype by which future relationships and interactions with others come to be understood.