1. in Kleinian analysis and Fairbairnian theory, a primitive defense mechanism used to protect oneself from conflict, in which objects provoking anxiety and ambivalence are dichotomized into extreme representations (part-objects) with either positive or negative qualities, resulting in polarized viewpoints that fluctuate in extremes of seeing the self or others as either all good or all bad. This mechanism is used not only by infants and young children, who are not yet capable of integrating these polarized viewpoints, but also by adults with dysfunctional patterns of dealing with ambivalence; it is often associated with borderline personality disorder. Also called splitting of the object.

2. in cotherapy, divisiveness that a client provokes between therapists to polarize them on treatment decisions and to undermine the therapeutic process. Also called splitting situation.