The concept of the undifferentiated matrix is later enlarged to denote the lack of differentiation between, and the existence of, the constitutional factors that later differentiate into the ego, id, and superego. Thus the psychic structure exists only in potential form for the neonate. However, the emphasis is obviously on the absence of boundaries in the sense of absence of differentiation, i.e., differentiation is seen as the development of boundaries. The undifferentiated matrix is characterized by a lack of differentiation between its various contents: between inner and outer, pleasant and painful, mind and body, libido and aggression, self and other, and so on. The development of the psychic structure and hence of the self-image is seen as a process of structuralization of the mind. In fact, object relations theory is primarily an understanding of how this structure develops out of an undifferentiated state of the mind.