ABSTRACT
We are at a crossroads of a scientific paradigm shift from reductionism to emergentism. The former focuses on the studies of the substance of entities, whereas the latter emphasizes on the principles of organization of these entities. The urban development process is characterized by the four Is: interdependence, irreversibility, indivisibility, and imperfect foresight. Together, the four Is prevent the fluid city from existing and result in the complexity of the city for which plans are useful. Complexity theory provides a set of useful ideas about cities because cities are now viewed as complex systems of numerous interacting decisions. Concepts derived from decision theory are important for us, at least conceptually, to understand how cities work and how we should plan for them effectively. Plans work under the condition of the four Is, which result in complex urban systems. That plans work in urban development is a claim that lacks theoretical and empirical backing. Based on a realistic model of cities as giant, dynamic networks of decisions in which plans and the planner are embedded, I provide a partial answer to this fundamental question by proving axiomatically that plans work in complex network systems of which cities are a manifestation. The theorem reached from the axiomatic system provides a theoretical basis for how planning is practiced. In particular, it implies that plan-based actions derived internally that consider multiple, linked decisions are more effective than decision-based actions that treat these decisions as independent, in particular in the face of complexity.
