Centralized, formal rules can facilitate productive activity by establishing roles and practices. The rules of baseball don't just regulate the behavior of the players; they determine the behavior that constitutes playing the game. Rules do not prevent people from playing baseball; they create the very practice that allows people to play baseball. A score of music imposes rules, but it also creates a pattern of conduct that enables people to produce music. Legal rules that enable the formation of corporations, that enable the use of wills and trusts, that create negotiable instruments, and that establish the practice of contracting all make practices that create new opportunities for individuals. And we have legal rules that establish roles individuals play within the legal system, such as judges, trustees, partners, and guardians. True, the legal rules that establish these roles constrain the behavior of individuals who occupy them, but rules also create the roles themselves. Without them an individual would not have the opportunity to occupy the role.