" In their ‘attempt to state explicitly and systematically that body of assumptions which constitutes psychoanalytic metapsychology’, Rapaport and Gill classify assumptions according to certain points of view. They identify five such viewpoints, each of which requires that whatever psychoanalytic explanation of a psychological phenomenon is offered must include propositions of a certain sort. The five viewpoints and the sort of proposition each demands are held to be the following: The Dynamic: This point of view demands propositions concerning the psychological forces involved in a phenomenon. The Economic: This demands propositions concerning the psychological energy involved in a phenomenon. The Structural: This demands propositions concerning the abiding psychological configurations (structures) involved in a phenomenon. The Genetic: This demands propositions concerning the psychological origin and development of a phenomenon. The Adaptive: This demands propositions concerning the relationship of a phenomenon to the environment. "

― John Bowlby , Attachment