Cite as: 521 U. S. 642 (1997)
Opinion of the Court
measure, because its mission is to prevent, typically encompasses more than the core activity prohibited. As we noted in Schreiber, § 14(e)'s rulemaking authorization gives the Commission "latitude," even in the context of a term of art like "manipulative," "to regulate nondeceptive activities as a 'reasonably designed' means of preventing manipulative acts, without suggesting any change in the meaning of the term 'manipulative' itself." 472 U. S., at 11, n. 11. We hold, accordingly, that under § 14(e), the Commission may prohibit acts not themselves fraudulent under the common law or § 10(b), if the prohibition is "reasonably designed to prevent . . . acts and practices [that] are fraudulent." 15 U. S. C. § 78n(e).18
Because Congress has authorized the Commission, in § 14(e), to prescribe legislative rules, we owe the Commission's judgment "more than mere deference or weight." Batterton v. Francis, 432 U. S. 416, 424-426 (1977). Therefore, in determining whether Rule 14e-3(a)'s "disclose or abstain from trading" requirement is reasonably designed to prevent fraudulent acts, we must accord the Commission's assessment "controlling weight unless [it is] arbitrary, capricious, or manifestly contrary to the statute." Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837, 844 (1984). In this case, we conclude, the Commission's assessment is none of these.19
was "to bar warehousing under its authority to regulate tender offers." 445 U. S., at 234. The Government acknowledges that trading authorized by a principal breaches no fiduciary duty. See Reply Brief 17. The instant case, however, does not involve trading authorized by a principal; therefore, we need not here decide whether the Commission's proscription of warehousing falls within its § 14(e) authority to define or prevent fraud.
18 The Commission's power under § 10(b) is more limited. See supra, at 651 (Rule 10b-5 may proscribe only conduct that § 10(b) prohibits).
19 Justice Thomas' dissent urges that the Commission must be precise about the authority it is exercising—that it must say whether it is acting to "define" or to "prevent" fraud—and that in this instance it has pur-
673
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