People and companies rely on public law when they plan their activities; society relies on legal entitlements when it adapts to new technology, economic conditions, and social groups; legislators, administrators, and judges rely on settled law when they pass, implement, and interpret statutes (respectively). Such private, societal, and public “reliance interests” are the “dark matter” of America’s law of interpretation. They underwrite most interpretive doctrine, and their perceived force broadly and deeply affects the application of doctrine.

Reliance interests anchor the constitutional bias in favor of interpretive continuity, and they provide guardrails for the leading theories of interpretation—namely—textualism or original public meaning, legal process or purposivism, and cost-benefit economic theory. Because reliance interests themselves evolve, they can also provide an orderly process for updating old norms, under whatever the predominant theory of interpretation might be.

Nonetheless, reliance interests do not always prevail. In recent statutory and constitutional decisions, the Roberts Court has applied traditional reliance interests selectively—a signal that the Court is introducing a regime change