WHY do our best-laid plans go oft astray? Cities enact rent control in order to ensure an adequate supply of affordable housing, which discourages further investment in residential property and makes affordable housing harder to find. We ban certain drugs in order to protect society from their adverse consequences, thereby encouraging an illegal narcotics traffic that enriches criminals, fuels urban violence, and complicates relations with foreign governments. We welcome the globalization of world markets and hail the Asian economic miracle, only to be surprised when a currency crisis in Thailand triggers a financial panic in Korea and Japan.
Why is the human experience filled with unpleasant surprises like these? The main reason, as Robert Jervis makes clear in his intriguing new book, System Effects, is the difficulty of predicting how complex systems will behave. Drawing on a diverse body of scholarly research and a wealth of illuminating examples, Jervis shows that "system effects" are an important and often overlooked part of social and political life. And though he focuses most of his attention on issues of international politics, where system effects are especially prevalent, his insights will capture the imagination of those who puzzle over other social problems as well.
For Jervis, a system effect exists whenever "(a) a set of units or elements is interconnected so that changes in some elements or their relations produce changes in other parts of the system, and (b) the entire system exhibits properties and behaviors that are different from those of the parts." Thus a system can be a physical entity, such as the solar system; a living organism; or a social organization, such as a free market, a neighborhood, or an international alliance. Although the boundaries between different systems are largely arbitrary (for example, individual human beings are systems in their own right and also part of a nearly infinite number of social systems), system effects will be present whenever separate parts are linked in a larger whole.