Opinion of the Court
assume, “absent a clearly expressed legislative intention to the contrary,” that “the legislative purpose is expressed by the ordinary meaning of the words used.” American Tobacco Co. v. Patterson, 456 U. S. 63, 68 (1982) (alterations omitted). Whatever the ultimate purpose of international organization immunity may be–the IOIA does not address that question–the immediate purpose of the immunity provision is expressed in language that Congress typically uses to make one thing continuously equivalent to another.
B
The more natural reading of the IOIA is confirmed by a canon of statutory interpretation that was well established when the IOIA was drafted. According to the “reference” canon, when a statute refers to a general subject, the statute adopts the law on that subject as it exists whenever a question under the statute arises. 2 J. Sutherland, Statutory Construction §§5207–5208 (3d ed. 1943). For example, a statute allowing a company to “collect the same tolls and enjoy the same privileges” as other companies incorporates the law governing tolls and privileges as it exists at any given moment. Snell v. Chicago, 133 Ill. 413, 437–439, 24 N. E. 532, 537 (1890). In contrast, a statute that refers to another statute by specific title or section number in effect cuts and pastes the referenced statute as it existed when the referring statute was enacted, without any subsequent amendments. See, e. g., Culver v. People ex rel. Kochersperger, 161 Ill. 89, 95–99, 43 N. E. 812, 814–815 (1896) (tax-assessment statute referring to specific article of another statute does not adopt subsequent amendments to that article).
Federal courts have often relied on the reference canon, explicitly or implicitly, to harmonize a statute with an external body of law that the statute refers to generally. Thus, for instance, a statute that exempts from disclosure
