When a court reviews an agency's construction of the statute which it administers, it is confronted with two questions. First, always, is the question whether Congress has directly spoken to the precise question at issue. If the intent of Congress is clear, that is the end of the matter; for the court,
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as well as the agency, must give effect to the unambiguously expressed intent of Congress. [Footnote 9] If, however, the court determines Congress has not directly addressed the precise question at issue, the court does not simply impose its own construction on the statute, [Footnote 10] as would be necessary in the absence of an administrative interpretation. Rather, if the statute is silent or ambiguous with respect to the specific issue, the question for the court is whether the agency's answer is based on a permissible construction of the statute. [Footnote 11]
"The power of an administrative agency to administer a congressionally created . . . program necessarily requires the formulation of policy and the making of rules to fill any gap left, implicitly or explicitly, by Congress."
Morton v. Ruiz,415 U. S. 199, 415 U. S. 231 (1974). If Congress has explicitly left a gap for the agency to fill, there is an express delegation
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of authority to the agency to elucidate a specific provision of the statute by regulation. Such legislative regulations are given controlling weight unless they are arbitrary, capricious, or manifestly contrary to the statute. [Footnote 12] Sometimes the legislative delegation to an agency on a particular question is implicit, rather than explicit. In such a case, a court may not substitute its own construction of a statutory provision for a reasonable interpretation made by the administrator of an agency. [Footnote 13]
We have long recognized that considerable weight should be accorded to an executive department's construction of a statutory scheme it is entrusted to administer, [Footnote 14] and the principle of deference to administrative interpretations
"has been consistently followed by this Court whenever decision as to the meaning or reach of a statute has involved reconciling conflicting policies, and a full understanding of the force of the statutory policy in the given situation has depended upon more than ordinary knowledge respecting the matters subjected to agency regulations. See, e.g., National Broadcasting Co. v. United States,319 U. S. 190; Labor Board v. Hearst Publications, Inc.,322 U. S. 111; Republic Aviation Corp. v.