This Article seeks to explain the puzzle of the divergence of American law from the rest of the common law world through the lens of legal theory. I argue that there are four competing ideal-type theories of the authority of the common law: reason, practice, custom, and will. The reason view explains the authority of the common law in terms of correspondence to the demands of pure practical reason; the practice view sees the authority of the common law as derived from the expertise of practitioners (especially judges and practice-oriented academics) who try to develop the common law as a slowly changing, historically binding tradition; the custom view sees the authority of the common law as derived from its correspondence to contemporaneous norms and values; and the will view sees the authority of the common law (like that of all other law) as derived from the acts of a sovereign. These competing views imply different answers to various questions (such as the relationship between statutes and the common law, or the role of judges in the legal system). They also lead to very different attitudes towards the idea of a single, supranational common law: generally speaking, the first two approaches are more sympathetic to common law convergence than the latter two. I argue that these days English common law is close to the second, practice-based conception of common law authority, whereas American law adopts a combination of the third and fourth conceptions. This explains why American common law is largely uninterested in maintaining commonality with other common law jurisdictions, as well as many other differences between American and English common law.
