This Article calls attention to a difference between the implementation of state statutes and the implementation of federal statutes. When a state legislature enacts a statute, the state's courts naturally draw upon overarching doctrines of unwritten law to handle various questions that intersect with the statute but that the statute does not specifically address. Courts tend to think of those doctrines as operating directly rather than through incorporation into each individual statute. Especially after Erie Railroad Co. v. Tompkins, however, the federal Supreme Court has felt pressure to adopt a different way of thinking about the interaction between federal statutes and the unwritten law. Erie raised the possibility that if a particular question lay beyond a federal statute's domain, judges might have to handle it according to a single state's version of the unwritten law. That result sometimes seemed inappropriate: there were certain questions that Congress was not in the habit of addressing, but that nonetheless seemed to have a federal character when they arose in connection with the implementation of a federal statute. To solve this potential problem, the Supreme Court began reading federal statutes to encompass various questions that might once have been thought to lie beyond their domains, and that were still thought to lie beyond the domains of analogous state statutes. This solution has continued to the present day. As a result, the Supreme Court routinely uses the rubric of statutory interpretation to handle questions that state courts treat as matters of unwritten law.

To illustrate this phenomenon, the Article contrasts the choice-of-law doctrines that state courts use to determine the applicability of their own state's statutes with the "presumption against extraterritoriality" that the Supreme Court uses to answer the same question in connection with federal statutes. After exploring this contrast in detail, the Article surveys an array of additional examples that share a similar structure.

The practical consequences of shoehorning general legal questions into the domains of individual federal statutes depend on the interpretive techniques that courts proceed to use to answer those questions. If courts hew closely to the literal language of the relevant statute, they may reach dramatically different results than traditional principles of unwritten law would suggest. Those differences will be muted if courts instead read individual federal statutes as implicitly incorporating background principles of unwritten law, or if courts develop canons of construction that approximate the same ideas. But even when courts use one of these latter techniques, the mechanism through which principles of unwritten law operate can have subtle but significant effects.

Caleb E. Nelson, State and Federal Models of the Interaction between Statutes and Unwritten Law, 80 University of Chicago Law Review, 657–767 (2013).
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