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This article argues that the agent-based computational model permits a distinctive approach to social science for which the term "generative" is suitable. In defend ing this terminology, features distinguishing the approach from both "inductive" and "deductive" science are given. Then, the following specific contributions to social science are discussed: The agent-based computational model is a new tool for empirical research. It offers a natural environment for the study of connection ist phenomena in social science. Agent-based modeling provides a powerful way to address certain enduring-and especially interdisciplinary-questions. It allows one to subject certain core theories-such as neoclassical microeconomics-to important types of stress (e.g., the effect of evolving preferences). It permits one to study how rules of individual behavior give rise-or "map up"-to macroscopic regularities and organizations. In turn, one can employ laboratory behavioral research findings to select among competing agent-based ("bottom up") models. The agent-based approach may well have the important effect of decoupling individual rationality from macroscopic equilibrium and of separating decision science from social science more generally. Agent-based modeling offers powerful new forms of hybrid theoretical-computational work; these are particularly relevant to the study of non-equilibrium systems. The agent-based approach invites the interpretation of society as a distributed computational device, and in turn the interpretation of social dynamics as a type of computation. This interpretation raises important foundational issues in social science-some related to intractability, and some to undecidability proper. Finally, since "emergence" *The author is a senior fellow in Economic Studies at The Brookings Institution and a member of the External Faculty of the Santa Fe Institute.

This article presents an agent-based computational model of civil violence. Two variants of the civil violence model are presented. In the first a central authority seeks to suppress decentralized rebellion. In the second a central authority seeks to suppress communal violence between two warring ethnic groups.