Introduction to Spin & Lattice Models in the Social Sciences

In recent years, political economists and other social scientists have begun adopting spin and lattice models into their theoretical tool kit. This article introduces examples of how these models are used. For illustration, a simple dynamical model of how legal rules evolve and propagate in the Anglo-American court system is described. Stanford Graduate School of Business. The author is pleased to acknowledge financial support from the John M. Olin Academic Year Fellowship in Law and Economics at Stanford Law School and the Santa Fe Institute’s Complex Systems Summer School. 1 The Common Law as an Evolutionary System Almost two centuries ago, Justice Oliver Wendell Holmes wrote “The life of the law has not been knowledge: it has been experience. The felt necessities of the time, ... avowed or unconscious, even the prejudices which judges share with their fellow men, have had a good deal more to do than the syllogism in determining the rules by which men [are] governed.” Likewise, the German legal scholar Friedrich Karl von Savigny wrote that “All law... is first developed by custom and [conventional morality], next by jurisprudence,—everywhere, therefore, by internal silently-operating powers, not by the arbitrary will of a law-giver.” (Yee 1998) Holmes’ “felt necessities” and von Savigny’s “internal silently-operating powers” have not gone unnoticed by modern scholars. Modern legal scholars, ranging from Grant Gilmore to Lawrence Friedman, have observed that changes in law at various times are “rapid and violent,” “clean and swift,” and “highly fluctuating” (Yee 2001). In current events, a growing branch of intellectual property, “cyberspace law,” has emerged almost overnight in response to technological innovations and business needs (Yee 1998). Moreover, capital markets anticipate such changes in a rational way (Yee 2000). Hence, it comes as no surprise that Holmes’ “felt necessities” and von Savigny’s “internal silently-operating powers” drive the basis of an evolutionary framework for understanding the developement the common law (Priest 1977; Rubin 1977; Yee 1998). The idea is based on Darwinian natural selection: efficient legal rules survive while inefficient rules are culled out by litigation. In