Courts engage in interstatutory cross-referencing all the time, relying on one statute to help interpret another. Yet, neither courts nor scholars have ever had a satisfactory theory for determining when it is appropriate. Is it okay to rely on any other statute as an interpretive aid? Or, are there limits to the practice? If so, what are they? To assess when interstatutory cross-referencing is appropriate, I focus on one common form of the technique, the in pari materia doctrine. When a court concludes that two statutes are in pari materia or (translating the Latin) “on the same subject,” the court then treats the two statutes as though they were one. The doctrine thus permits judges to use ordinary doctrines of intra-statute interpretation across the two statutes. Determining that two statutes are “on the same subject” thus gives interpreters a powerful tool of interstatutory interpretation.
How, then, should courts determine whether to treat two statutes as one? If we frame the question through the lens of the two currently predominant theories of statutory interpretation — textualism and intentionalism—we can see that the traditional approach of asking about the statutes’ “subject matter” in the abstract makes little sense. For textualist judges who care about objective meaning, it makes more sense to engage in interstatutory cross-referencing if and only if the audience for the two statutes—the appropriately informed objective reader of the statutes—is the same. For interpreters who care about subjective legislative intent, interstatutory cross-referencing would generally be appropriate if and only if the two statutes were drafted by and came through the same Congressional committees.
Even if one rejects my proposed approaches, thinking about how to fit interstatutory cross-referencing into modern theories of statutory interpretation raises some confounding issues for those theories. In particular, it requires textualists to articulate explicitly who the audience for any given statute is, for without doing so, the textualist has no theoretical basis for determining when interstatutory cross-referencing is appropriate and when it is not. Thus, irrespective of the specifics of my proposals, looking at the ancient doctrine of in pari materia through the lens of modern theories of statutory interpretation sheds light on important questions about statutory interpretation that courts and theorists have largely ignored.