Notes to Chapter 1

Note 1.1: The meaning of complexity

Complexity is a term with several related meanings. This note explores three major sets of definitions so that perspective can be gained on the approach followed in this book.

Structural complexity concerns properties of a system at one point in time; dynamic or behavioral complexity refers to the behavior of a system over time generated by the rules of the system; and subjective complexity focuses either on the way in which the system is perceived by others or to properties of the system that arise not from any particular rules but from the purposes and goals of individuals in the system. Unfortunately, this terminology is not standardized. For instance, paralleling my distinction between “structural” and “behavior” complexity, Alexei N. Severtsov distinguishes between “morphological” and “biological” complexity (Urbanek, 1988). McShea (1991) calls “structural complexity” what I call “behavioral complexity.” If I understand him correctly, Çambel, (1993) calls “static complexity” what I designate “subjective complexity.”

Dynamic complexity focuses particularly on the self-organizing behavior of systems. For instance, biologists have investigated how birds flock together again after they fly around obstacles and chemists have investigated how systems behave when they are far from equilibrium (Nicolis and Prigogine, 1989). In both cases the self-organization is generated by the nonlinear equations describing the system. Along the same lines economists have examined sunspot equilibria, speculative bubbles on the stock market, unemployment as a hysteresis phenomenon, and more general path-dependent historical processes such as the adoption of particular standards or technologies (e.g., Anderson, Arrow, and Pines, 1988; Barnett, Geweke, and Shell, 1989; David, 1985).