A patient with Borderline Personality Disorder frequently idealizes her therapist during one session, describing them as "the only one who truly understands me," but then demonizes them in the next, accusing them of being "uncaring and incompetent." This pattern of perceiving others as either entirely good or entirely bad is best described by which of the following defense mechanisms?

Explanation

Splitting is a primitive defense mechanism commonly observed in Borderline Personality Disorder. It involves the inability to integrate positive and negative qualities of oneself or others into a cohesive whole, leading to an "all good" or "all bad" perception. The patient's rapid shift from idealization to devaluation of the therapist is a classic example of splitting. Repression involves unconsciously blocking unacceptable thoughts or feelings. Projection involves attributing one's own unacceptable thoughts or feelings to another person. Rationalization involves creating logical but false explanations for one's behavior.