Opinion of the Court
ments” did not mean “virtually absolute immunity.” The phrase is not a term of art with substantive content, such as “fraud” or “forgery.” See id., at 22; Gilbert v. United States, 370 U. S. 650, 655 (1962). It is rather a concept that can be given scope and content only by reference to the rules governing foreign sovereign immunity. It is true that under the rules applicable in 1945, the extent of immunity from suit was virtually absolute, while under the rules applicable today, it is more limited. But in 1945, as today, the IOIA’s instruction to grant international organizations the immunity “enjoyed by foreign governments” is an instruction to look up the applicable rules of foreign sovereign immunity, wherever those rules may be found–the common law, the law of nations, or a statute. In other words, it is a general reference to an external body of (potentially evolving) law.
C
In ruling for the IFC, the D. C. Circuit relied upon its prior decision in Atkinson, 156 F. 3d 1335. Atkinson acknowledged the reference canon, but concluded that the canon’s probative force was “outweighed” by a structural inference the court derived from the larger context of the IOIA. Id., at 1341. The Atkinson court focused on the provision of the IOIA that gives the President the authority to withhold, withdraw, condition, or limit the otherwise applicable privileges and immunities of an international organization, “in the light of the functions performed by any such international organization.” 22 U. S. C. §288. The court understood that provision to “delegate to the President the responsibility for updating the immunities of international organizations in the face of changing circumstances.” Atkinson, 156 F. 3d, at 1341. That delegation, the court reasoned, “undermine[d]” the view that Congress intended the IOIA to in effect update itself by incorporating changes in the law governing foreign sover-
