Numerous authors have theorized that defense mechanisms play a role in personality disorders. We reviewed theoretical writings and empirical studies about defenses in schizotypal, borderline, antisocial, and narcissistic personality disorders, developing hypotheses about these differential relationships. We then examined these hypotheses using dynamic interview data rated for defenses in a study of participants (n = 107) diagnosed with these four personality disorder types. Overall, the prevalence of immature defenses was substantial, and all four disorders fit within the broad borderline personality organization construct. Defenses predicted the most variance in borderline and the least variance in schizotypal personality disorder, suggesting that dynamic factors played the largest role in borderline and the least in schizotypal personality. Central to borderline personality were strong associations with major image-distorting defenses, primarily splitting of self and other's images, and the hysterical level defenses, dissociation and repression. Narcissistic and antisocial personality disorders shared minor image-distorting defenses, such as omnipotence or devaluation, while narcissistic also used splitting of self-images and antisocial used disavowal defenses like denial. Overall, differential relationships between specific defenses and personality disorder types were largely consistent with the literature, and consistent with the importance that the treatment literature ascribes to working with defenses.

We examined whether borderline personality disorder (BPD) and antisocial personality disorder (APD) could be differentiated based on defense mechanisms as measured by observer (Defense-Q; MacGregor, Olson, Presniak, & Davidson, 2008) and self-report (Defense Style Questionnaire; Andrews, Singh, & Bond, 1993) measures. We conducted 2 studies whereby nonclinical participants were divided into borderline and antisocial groups based on scores from the Personality Assessment Inventory (Morey, 1991). Multivariate analysis of variance results revealed significant overall group differences in defense use. Univariate analyses further showed group differences on several individual defenses (e.g., acting out, denial, and turning against self). Together, the findings suggest that in BPD, the defenses may emphasize interpersonal dependency and a tendency to direct aggression toward the self; whereas in APD, the defenses may emphasize egocentricity, interpersonal exploitation, and a tendency to direct aggression toward others. Overall, this study demonstrates important differences in defense use between borderline and antisocial personality groups across both observer and self-report measures.

Defense interpretations are commonly used techniques that clinicians employ more frequently than transference interpretations. How and when clinicians interpret defenses, however, has received little empirical examination. In an effort to facilitate the empirical study of defense interpretation, we reviewed 15 works by noted authors who gave a prominent role to interpreting defenses in discussing clinical work in general patient populations. Our goal was to identify and systematize distinct themes from these authors that might be testable hypotheses. We identified 74 themes related to the interpretation of defenses in psychotherapy-for example, "interpreting too frequently diminishes the emotional impact of interpretation"-which we organized into 17 distinct categories (e.g., factors associated with positive outcome). We subsequently selected 19 themes that were readily operationalizable as hypotheses and examination of which would advance clinical practice. These hypotheses address issues such as when, in what order, and how to interpret defensive material and what successful outcomes would be. We then describe prototypes of research designs, employing naturalistic observation, randomized controlled trials, or experimental laboratory studies, which could investigate these important hypotheses. Overall, this report codifies current clinical maxims and then provides future research directions for determining how clinicians can most effectively address defenses in psychotherapy.