ACCORDING TO WIKIPEDIA
Splitting (also called black and white thinking or all-or-nothing thinking) is the failure in a person’s thinking to bring together both positive and negative qualities of the self and others into a cohesive, realistic whole. It is a common defense mechanism used by many people. The individual tends to think in extremes (i.e., an individual’s actions and motivations are all good or all bad with no middle ground.)
The concept of splitting was developed by Ronald Fairbairn in his formulation of object relations theory; it begins as the inability of the infant to combine the fulfilling aspects of the parents (the good object) and their unresponsive aspects (the unsatisfying object) into the same individuals, but sees the good and bad as separate. In psychoanalytic theory this functions as a defense mechanism. It is a relatively common defense mechanism for people with borderline personality disorder in DSM-IV-TR.