In the interest of clarifying the distinction between psychopathology based on structural conflict and psychopathology rooted in an arrest in ego development, the hypothesis is offered that there is a developmental line for each defensive process and that a defense mechanism represents the endpoint of a series of developmental achievements. Clinical material is presented to demonstrate the decisive diagnostic and therapeutic consequences of distinguishing between the defenses of projection, incorporation, and splitting, on the one hand, and their specific developmental prestages, on the other.