1998; Prigogine, 1967, 1980). For example, termites build the largest structures on earth when compared with the height of the builders, yet there is no CEO termite. Similarly, there is no central controller for the stock market, the Internet, or the food supply of New York City.

• Context and embeddedness. Systems exist within systems, and this matters. For example, global stock markets are linked such that if the currency of Thailand falls, the U.S. stock market reacts. In a machine, one can extract the parts and characterize the response of a part to a stimulus. Although one can study the parts of a CAS independently, its context matters in fundamental ways.

• Co-evolution. A CAS moves forward through constant tension and balance. Fires, though destructive, are essential to a healthy, mature forest. Competition is good for industries. Tension, paradox, uncertainty, and anxiety are healthy things in a CAS. In machine thinking, they are to be avoided.

With challenges that naturally fall in the zone of complexity, such as the design of the 21st-century health care system, it is not surprising if the system does not act like a machine. CAS science and the Stacey diagram suggest additional metaphors to assist our thinking. Box-B-1 highlights some key ideas that emerge from the application of CAS science to the challenges of designing the 21st-century health care system.

It is more helpful to think like a farmer than an engineer or architect in designing a health care system. Engineers and architects need to design every detail of a system. This approach is possible because the responses of the component parts are mechanical and, therefore, predictable. In contrast, the farmer knows that he or she can do only so much. The farmer uses knowledge and