Lester Luborsky's core conflictual relationship theme (CCRT; 1977) method of evaluating relationship patterns of therapy patients makes an important assumption, which this article examines theoretically and empirically: that patients in psychotherapy routinely describe themselves in an interactive relationship with others, rather than as people acting and reacting in isolation. Kleinian and Mahlerian psychoanalytic theories hold that the capacity for interaction or relatedness is not a given but a developmental achievement, an increasing function of differentiation. An enhancement of the CCRT approach, called the coherence of the relationship theme (CRT), is introduced here. It measures the degree to which patients describe themselves and others in interaction. It is predicted and empirically observed that interaction and relatedness as measured by the CRT increase with differentiation, supporting the proposal that the CRT is a meaningful measure of a capacity for relatedness, and a useful enhancement of the CCRT system.