Full context:   Loevinger describes the ego as a process, rather than a thing; it is the frame of reference (or lens) one uses to construct and interpret one's world. This contains impulse control and character development with interpersonal relations and cognitive preoccupations, including self-concept. Sullivan (1958) proposed four levels of "interpersonal maturity and interpersonal integration": impulsive, conformist, conscientious, and autonomous. Developing from that initial framework, Loevinger completed a developmental model of nine sequential stages, each representing a progressively more-complex way of perceiving oneself in relation to the world. Every stage provides a frame of reference to organize and define experience over an individual's life: "Since each new ego stage or frame of reference builds on the previous one and integrates it, no one can skip a stage ... One has not yet acquired the interpersonal logic."