ABSTRACT
All structures are constantly subject to forces that may result in changes in their organizational form. A complete theory of psychological structures must therefore account for both: (1) structural stability (i.e., those conditions that make it possible for a particular structure to resist these pressures toward change when they are in fact resisted); and (2) systematic variability (i.e., those conditions that determine the onset, direction, rate, and termination of such changes when they occur).
