The aim of this talk to offer a formal understanding of common law reasoning – especially the nature of this reasoning, but also its point, or justification, in terms of social coordination. I will present two, possibly three, formal models of the common law, and argue for one according to which courts, are best thought of, not as creating and modifying rules, but as generating a priority ordering on reasons. The talk is not technical, although it draws on tiny bits of logic, and also on work in AI and Law; it contributes to legal theory, and also, possibly, to applied ethics.