Opinion of the Court

an agency official does not authorize a court to read a regulation inconsistently with its language.8

In sum, the text of the 1980 PSD regulations on "modification" doomed the Court of Appeals's attempt to equate those regulations with their NSPS counterpart. As a consequence, we have to see the Court of Appeals's construction of the 1980 PSD regulations as an implicit invalidation of those regulations, a form of judicial review implicating the provisions of §307(b) of the Act, which limit challenges to the validity of a regulation during enforcement proceedings when such review "could have been obtained" in the Court of Appeals for the District of Columbia Circuit within 60 days of EPA rulemaking. See 42 U. S. C. § 7607(b); see also United States v. Cinergy Corp., 458 F. 3d 705, 707-708 (CA7 2006); Wisconsin Elec. Power Co., 893 F. 2d, at 914, n. 6. Because the Court of Appeals did not believe that its analysis reached validity, it did not consider the applicability or effect of that limitation here. We have no occasion at this point to consider the significance of § 307(b) ourselves.

IV

Finally, Duke assumes for argument that the Act and the 1980 regulations may authorize EPA to construe a PSD "modification" as it has done, but it charges that the agency has taken inconsistent positions and is now "retroactively

8 Duke now offers an alternative argument for applying the hourly emissions test for the PSD program: before a project can become a "major modification" under the PSD regulations, 40 CFR §51.166(b)(2)(i) (1987), it must meet the definition of "modification" under the NSPS regulations, § 60.14(a). That sounds right, but the language of the regulations does not support it. For example, it would be superfluous for PSD regulations to require a "major modification" to be a "physical change in or change in the method of operation," §51.166(b)(2)(i), if they presupposed that the NSPS definition of "modification," which contains the same prerequisite, § 60.14(a), had already been satisfied. The NSPS and PSD regulations are complementary and not related as set to subset.

THOMAS, J., concurring in part

targeting twenty years of accepted practice." Brief for Respondent Duke 37; see also Brief for State of Alabama et al. as Amici Curiae. This claim, too, has not been tackled by the District Court or the Court of Appeals; to the extent it is not procedurally foreclosed, Duke may press it on remand.

The judgment of the Court of Appeals is vacated, and the case is remanded for further proceedings consistent with this opinion.

JUSTICE THOMAS, concurring in part.

It is so ordered.

I join all but Part III-A of the Court's opinion. I write separately to note my disagreement with the dicta in that portion of the opinion, which states that the statutory cross-reference does not mandate a singular regulatory construction.

The Prevention of Significant Deterioration (PSD) statute explicitly links the definition of the term "modification" to that term's definition in the New Source Performance Standard (NSPS) statute:

"The term 'construction' when used in connection with any source or facility, includes the modification (as defined in section 7411(a) of this title) of any source or facility." 42 U. S. C. § 7479(2)(C).

Section 7411(a) contains the NSPS definition of "modification," which the parties agree is the relevant statutory definition of the term for both PSD and NSPS. Because of the cross-reference, the definitions of "modification" in PSD and NSPS are one and the same. The term "modification" therefore has the same meaning despite contextual variations in the two admittedly different statutory schemes. Congress' explicit linkage of PSD's definition of "modification" to NSPS' prevents the Environmental Protection

THOMAS, J., concurring in part

Agency (EPA) from adopting differing regulatory definitions of "modification" for PSD and NSPS. Cf. IBP, Inc. v. Alvarez, 546 U. S. 21, 34 (2005) (concluding that an "explicit reference" to a previous statutory definition prohibits interpreting the same word differently).

Section 7479(2)(C)'s cross-reference carries more meaning than the mere repetition of the same word in a different statutory context. When Congress repeats the same word in a different statutory context, it is possible that Congress might have intended the context to alter the meaning of the word. See Atlantic Cleaners & Dyers, Inc. v. United States, 286 U. S. 427, 433 (1932). No such possibility exists with § 7479(2)(C). By incorporating NSPS' definition of “modification," Congress demonstrated that it did not intend for PSD's definition of "modification" to hinge on contextual factors unique to the PSD statutory scheme. Thus, United States v. Cleveland Indians Baseball Co., 532 U. S. 200 (2001), which analyzes the mere repetition of the same word in a different statutory context, carries little weight in this situation.

Likewise, this case differs from the circumstance we faced in Robinson v. Shell Oil Co., 519 U. S. 337 (1997). In Robinson, we considered whether "employee," as used in §704(a) of Title VII of the Civil Rights Act of 1964, included former employees. We determined that under the clear language of the statute, certain statutory provisions using the term "employee" made sense only with respect to former employees or current employees, but not both. Id., at 342-343. Accordingly, upon analyzing the context of § 704(a), we were compelled to conclude that the term "employee" included former employees. This case does not present a similar situation. The statute here includes a statutory cross-reference, which conveys a clear congressional intent to provide a common definition for the term "modification." And the contextual differences between PSD and NSPS do not compel

THOMAS, J., concurring in part

different meanings for the term "modification." Robinson is, therefore, inapplicable.

Even if the cross-reference were merely the equivalent of repeating the words of the definition, we must still apply our usual presumption that the same words repeated in different parts of the same statute have the same meaning. See Atlantic Cleaners, supra, at 433; ante, at 574. That presumption has not been overcome here. While the broadly stated regulatory goals of PSD and NSPS differ, these contextual differences do not compel different definitions of "modification." That is, unlike in Robinson, reading the statutory definition in the separate contexts of PSD and NSPS does not require different interpretations of the term “modification." EPA demonstrated as much when it recently proposed regulations that would unify the regulatory definitions of "modification." See 70 Fed. Reg. 61083, n. 3 (2005) (terming the proposal "an appropriate exercise of our discretion" and stating that the unified definition better serves PSD's goals).

The majority opinion does little to overcome the presumption that the same words, when repeated, carry the same meaning. Instead, it explains that this Court's cases do not compel identical language to be interpreted identically in all situations. Granting that point, the majority still has the burden of stating why our general presumption does not control the outcome here. It has not done so.

REPORTER'S NOTE

The next page is purposely numbered 801. The numbers between 584 and 801 were intentionally omitted, in order to make it possible to publish the orders with permanent page numbers, thus making the official citations available upon publication of the preliminary prints of the United States Reports.