silentio to enact statutory language that it has earlier discarded in favor of other language." Nachman Corp. v. Pension Benefit Guaranty Corporation, 446 U. S. 359, 392-393 (1980) (Stewart, J., dissenting); cf. Gulf Oil Corp. v. Copp Paving Co., 419 U. S. 186, 200 (1974); Russello v. United States, 464 U. S., at 23.

IV

The INS makes two major arguments to support its contention that we should reverse the Court of Appeals and hold that an applicant can only show a "well-founded fear of persecution" by proving that it is more likely than not that he or she will be persecuted. We reject both of these arguments: the first ignores the structure of the Act; the second misconstrues the federal courts' role in reviewing an agency's statutory construction.

First, the INS repeatedly argues that the structure of the Act dictates a decision in its favor, since it is anomalous for § 208(a), which affords greater benefits than § 243(h), see n. 6, supra, to have a less stringent standard of eligibility. This argument sorely fails because it does not take into account the fact that an alien who satisfies the applicable standard under § 208(a) does not have a right to remain in the United States; he or she is simply eligible for asylum, if the Attorney General, in his discretion, chooses to grant it. An alien satisfying § 243(h)'s stricter standard, in contrast, is automatically entitled to withholding of deportation.28 In Matter of Salim, 18 I. & N. Dec. 311 (1982), for example, the Board held that the alien was eligible for both asylum and withholding of deportation, but granted him the more limited remedy only, exercising its discretion to deny him asylum. See also Walai v. INS, 552 F. Supp. 998 (SDNY 1982); Mat

"There are certain exceptions, not relevant here. See, e. g., § 243(h) (2)(A) (alien himself participated in "the persecution of any person. . ."); § 243(h)(2)(B) (alien was convicted of "serious crime" and "constitutes a danger to the community of the United States").

ter of Shirdel, Interim Decision No. 2958 (BIA Feb. 21, 1984). We do not consider it at all anomalous that out of the entire class of "refugees," those who can show a clear probability of persecution are entitled to mandatory suspension of deportation and eligible for discretionary asylum, while those who can only show a well-founded fear of persecution are not entitled to anything, but are eligible for the discretionary relief of asylum.

There is no basis for the INS's assertion that the discretionary/mandatory distinction has no practical significance. Decisions such as Matter of Salim, supra, and Matter of Shirdel, supra, clearly demonstrate the practical import of the distinction. Moreover, the 1980 Act amended § 243(h) for the very purpose of changing it from a discretionary to a mandatory provision. See supra, at 428-429. Congress surely considered the discretionary/mandatory distinction important then, as it did with respect to the very definition of "refugee" involved here. The House Report provides:

"The Committee carefully considered arguments that the new definition might expand the numbers of refugees eligible to come to the United States and force substantially greater refugee admissions than the country could absorb. However, merely because an individual or group comes within the definition will not guarantee resettlement in the United States." H. R. Rep., at 10.

This vesting of discretion in the Attorney General is quite typical in the immigration area, see, e. g., INS v. Jong Ha Wang, 450 U. S. 139 (1981). If anything is anomalous, it is that the Government now asks us to restrict its discretion to a narrow class of aliens. Congress has assigned to the Attorney General and his delegates the task of making these hard individualized decisions; although Congress could have crafted a narrower definition, it chose to authorize the At

torney General to determine which, if any, eligible refugees should be denied asylum.

The INS's second principal argument in support of the proposition that the "well-founded fear" and "clear probability" standard are equivalent is that the BIA so construes the two standards. The INS argues that the BIA's construction of the Refugee Act of 1980 is entitled to substantial deference, even if we conclude that the Court of Appeals' reading of the statutes is more in keeping with Congress' intent." This argument is unpersuasive.

"In view of the INS's heavy reliance on the principle of deference as described in Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984), we set forth the relevant text in its entirety:

"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, as well as the agency, must give effect to the unambiguously expressed intent of Congress. 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, 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.

""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, 231 (1974). If Congress has explicitly left a gap for the agency to fill, there is an express delegation 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. 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.

"We have long recognized that considerable weight should be accorded to an executive department's construction of a statutory scheme it is

The question whether Congress intended the two standards to be identical is a pure question of statutory construction for the courts to decide. Employing traditional tools of statutory construction, we have concluded that Congress did not intend the two standards to be identical.30 In Chevron

entrusted to administer, 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. . . .

"... If this choice represents a reasonable accommodation of conflicting policies that were committed to the agency's care by the statute, we should not disturb it unless it appears from the statute or its legislative history that the accommodation is not one that Congress would have sanctioned.' United States v. Shimer, 367 U. S. 374, 382, 383 (1961).

"Accord, Capital Cities Cable, Inc. v. Crisp, [467 U. S. 691, 699-700 (1984)].

"In light of these well-settled principles it is clear that the Court of Appeals misconceived the nature of its role in reviewing the regulations at issue. Once it determined, after its own examination of the legislation, that Congress did not actually have an intent regarding the applicability of the bubble concept to the permit program, the question before it was not whether in its view the concept is 'inappropriate' in the general context of a program designed to improve air quality, but whether the Administrator's view that it is appropriate in the context of this particular program is a reasonable one. Based on the examination of the legislation and its history which follows, we agree with the Court of Appeals that Congress did not have a specific intention on the applicability of the bubble concept in these cases, and conclude that the EPA's use of that concept here is a reasonable policy choice for the agency to make." Id., at 842-845 (citations and footnotes omitted).

"An additional reason for rejecting the INS's request for heightened deference to its position is the inconsistency of the positions the BIA has taken through the years. An agency interpretation of a relevant provision which conflicts with the agency's earlier interpretation is "entitled to considerably less deference" than a consistently held agency view. Watt v. Alaska, 451 U. S. 259, 273 (1981); see also General Electric Co. v. Gilbert, 429 U. S. 125, 143 (1976).

U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984), we explained:

"The judiciary is the final authority on issues of statutory construction and must reject administrative constructions which are contrary to clear congressional

The BIA has answered the question of the relationship between the objective § 243(h) standard and the fear-based standard of §§ 203(a)(7), 208, and the United Nations Protocol in at least three different ways. During the period between 1965, when § 203(a)(7) was enacted, and 1972, the BIA expressly recognized that § 203(a)(7) and § 243(h) prescribed different standards. See supra, at 433-434. Moreover, although the BIA decided in 1973 that the two standards were not irreconcilably different, see Matter of Dunar, 14 I. & N. Dec. 310 (1973), as of 1981 the INS was still instructing its officials to apply a "good reason" test to requests for asylum from aliens not within the United States. See Dept. of Justice, INS Operating Instructions Regulations TM 101, § 208.4, p. 766.9 (Nov. 11, 1981) (explaining that "well-founded fear" is satisfied if applicant "can show good reason why he/she fears persecution"). In 1984, when this case was decided by the BIA, it adhered to the view that the INS now espousescomplete identity of the standards. In 1985, however, the BIA decided to reevaluate its position and issued a comprehensive opinion to explain its latest understanding of the "well-founded fear" standard. Matter of Acosta, Interim Decision No. 2986 (Mar. 1, 1985).

In Acosta, the BIA noted a number of similarities between the two standards and concluded that in practical application they are "comparable" or "essentially comparable," and that the differences between them are not "meaningful," but the agency never stated that they are identical, equivalent, or interchangeable. On the contrary, the Acosta opinion itself establishes that the two standards differ. In describing the objective component of the asylum standard, the BIA concluded that the alien is not required to establish the likelihood of persecution to any "particular degree of certainty." Id., at 22. There must be a "real chance" that the alien will become a victim of persecution, ibid., but it is not necessary to show "that persecution is more likely than not' to occur." Id., at 25. The Acosta opinion was written after we had decided in Stevic that the § 243(h) standard "requires that an application be supported by evidence establishing that it is more likely than not that the alien would be subject to persecution," 467 U. S., at 429-430. The decision in Acosta and the long pattern of erratic treatment of this issue make it apparent that the BIA has not consistently agreed, and even today does not completely agree, with the INS's litigation position that the two standards are equivalent.