A complete description of adolescence may be made using a conceptual model that connects two kinds of system, open and closed. Far from representing diagnostic categories, these systems are constructions illustrating different adaptive choices available to adolescents at a critical time in their development. Open systems indicate the effort to transform the self, while closed systems indicate a need to control, force and change other people. Reference to both these systems has profound implications for practice and theory, not least because they provide a different way of looking at adolescence, the goal no longer being separation, but rather transformation.