Thus, according to ego psychology, a stable sense of identity or separate self is not something that the human being is born with, but is a result of a developmental process—what Mahler has called separation-individuation. At birth there is no awareness of an entity that is separate from its environment. A psychologically separate identity develops slowly as the infant interacts with its environment, especially with its mother. Thus the identity, with its mental apparatus (psychic structure), is a construction in the mind. The particular structure of the mind, the particular patterning of the content of the psyche (ultimately resulting in the sense of self), is something that develops, something that grows. It is then something not ready-made at physical birth. This is why Mahler speaks of “psychological birth.”

As we discussed in Chapter Two, the accomplishment of separation-individuation is understood to be the acquiring of independence from the mothering person in the process of forming a stable self-image and sense of self. Its final outcome is indeed the achievement of individuality, the capacity to be a person in one’s own right and to function autonomously. Thus, in terms of ego development, acquiring autonomy is the same as the achievement of the intrapsychic task of the separation-individuation process, the attainment of identity, separateness and individuality. We can see then that society’s idealization of autonomy points to the deeper significance of the desire of the man of the world for autonomy: it means to him becoming “his own person.” It means individuation, growth and maturity. Independence and autonomy within society, “making it,” achieving the capacity to support oneself and one’s family, the ability to make free choices about one’s life, are the adult’s expression of individuation, signs of the maturity of his ego development, and the fruition of the solidification of his individuality. The findings of object relations theory, however, show that these phenomena which are taken by society to indicate autonomy may only be skin deep. These findings identified a more basic level of autonomy, that of emotional independence, as the core of actual autonomy.

Generally speaking, when an adult wants to resist separation and individuation, he resorts primarily to negative merging. Negative merging is still merging. One can always activate it at times of separation anxiety. It is painful, manifesting in frustrating affects and emotional conflicts, but when it is used for defense against separation, one feels mother is around, and therefore feels secure in some way, even though the mother might be angry or hateful. . . . . . . Using negative merging as a defense against separation usually manifests as clinging to, or regressing to, negative patterns, manifestations, and relationships. In developmental psychology the phenomenon we are calling negative merging is thought to be always defended against. We find that it is most of the time defended against, but frequently it is employed, in a disguised form, as a defense against separation and its anxieties.

However, the stage of developing essential aspects shifts the inner work on the personality from the superego more to the structure of the ego itself. We have seen, for example, that the merging essence is related psychologically to the symbiotic stage, of fundamental importance for the development of ego structure. Other aspects of essence are connected to different phases of ego development or to different sectors of its structure. Essential strength is connected, for example, to the differentiation subphase of the separation-individuation process of ego development, when the infant begins to perceive that his mother and he are two people. Joy and value are essential aspects related more to the practicing subphase of this developmental process, when the toddler is joyously exploring his capacities and environment. The separation-individuation process leads ultimately to the development of the ego as a structure. Its final phase is that of object constancy, when the ego is formed and established as a permanent existence, separate from the environment (mother), and other people are seen to have separate existences. Finally, the ego is structured and developed, and the child permanently experiences himself as having a separate identity. The ego is seen here in a central position because everything else is really part of its structure. The ego is the product of the child's development.

The individuality of ego, the main outcome of the separation-individuation process, is primarily defined by Its boundaries. This individuality is dependent on the internalization of mother’s image and her soothing functions. However, the soothing functions, in terms of inner experience, are those of the Merging Essence, which is characterized by the absence of individual boundaries and separateness.