A popular slang definition of the verb to split is "to depart," or "to leave." In this context, to split describes the occasional wish of a psychiatrist who may be mired in the chaos created by the behavior of a patient diagnosed with borderline personality disorder. The primary definition of to split is "to divide sharply or cleanly." The ego mechanism of "splitting" is derived from the latter definition.

In this context, splitting refers to a primitive mechanism of defense characterized by a polarization of good feelings and bad feelings, of love and hate, of attachment and rejection. Splitting, archetypally imbedded in a patient's psychic structure, acts as a powerful unconscious force to protect against the ego's perception of dangerous anxiety and intense affects. Rather than providing real protection, splitting leads to destructive behavior and turmoil in patients' lives, and the often confused reactions manifested by those who try to help.

Some degree of splitting is an expectable part of early psychic development. We see it in young children who, early on, press us to tell them "Is it good?" or "Is it bad?" We hear their frustration when we answer, "Situations are not black or white; life is more complicated!" "Yes, I know all that," they say, "now tell me, is it good or is it bad?"

Subsequent developmental advances foster the ego's ability to accept paradoxical affects, and to synthesize and integrate good and bad, love and hate along with the associated affects. The need for a definite "yes" or "no" decreases, and multiple possibilities and variations on a theme become tolerable.

The expression splitting has become a part of the vernacular of everyday life. Despite its psychoanalytic origins, even those who are psychodynamic nihilists find it natural to describe those patients who are creating chaos on the ward or in life by the terms: "he splits," "she splits" or "they split." In this context, they are referring to a split in the hospital community provoked by the patients' behavior.

A familiar scenario follows: A patient, struggling with inner turmoil, finds someone on the ward who seems responsive to his or her needs, idealizes that staff member and invests this person with strength, love and power. The staff member, standing beneath this shining light, finds it hard to resist the temptation to accept as reality the wondrous feelings of idealized specialness. Whatever tensions might exist on the ward are magnified by a subtle intensification or manipulation of those who are experienced as good and those who are determined to be bad.

Inevitably, the staff member betrays the patient's idealization by some evidence of human frailty. The patient, overcome by the intense affects and anxiety this evokes, turns on the person as he would a deadly enemy and attacks. The patient then goes off in search of someone else to idealize and use as protection. The staff member feels demeaned, humiliated and attacked.