Kernberg’s major contributions have stemmed from his work on the psychoanalysis and psychotherapeutic treatment of patients with severe character disorders, particularly those with borderline personality organization (Kernberg, 1968), as well as patients with narcissistic character.
The primitive defenses of splitting and projective identi-fication, first described by Klein, are central to the diagnosis of borderline personality disorder as conceived by Kernberg (1979). His depiction of the landscape of the mind also owes some of its salient features to Jacobson, who first suggested that inter-nal representations of self and object with an associated affect are the nuclei of the early development of the psyche. Kernberg’s depiction of the inner world of borderline and psychotic patients is, however, uniquely his own. Splitting breaks up the internal representation of objects and of the self into part object represen-tations, each with an associated affect. The central feature of pro-jective identification, a primitive defense according to Kernberg, is that it always involves the projection of an internal object rela-tion with its associated affect. When projection is effective, the subject eliminates the unacceptable impulse or idea from any connection with the self. In contrast, in projective identifica-tion, the connection to the unacceptable contents is preserved along with the tie between the part self and the part object. The connection cannot be totally eliminated.
Kernberg envisioned the inner world of the borderline or psychotic patient as being populated by numerous unintegrated part self–part object dyads that are each linked by a predominant affect. These internal nuclei are kept separate by the defense of splitting. The borderline individual projects these pathological inner contents onto any significant other with whom he or she interacts. Which of these self-object–affect structures is active can shift from moment to moment; this results in the chaotic and shifting pattern of relationships that is the essence of what is ob-served clinically in patients with borderline psychopathological disorders (who can be described as being stably unstable).