the ego is able to introject and establish the complete object and to go through the depressive position… My hypothesis of the infantile depressive position is based on fundamental psychoanalytic concepts regarding the early stages of life
Klein grounds the depressive position in the ego’s capacity to integrate the whole object, tracing its theoretical foundations to Freud and Abraham’s work on primary introjection and oral libido, and identifying regression from it as a key pathogenic mechanism.
, Envy and Gratitude and Other Works 1946-1963, 1957thesis