Cite as: 511 U. S. 600 (1994)
Opinion of the Court
ment. In such a case, the usual presumption that a defendant must know the facts that make his conduct illegal should apply.
III
In short, we conclude that the background rule of the common law favoring mens rea should govern interpretation of § 5861(d) in this case. Silence does not suggest that Congress dispensed with mens rea for the element of § 5861(d) at issue here. Thus, to obtain a conviction, the Government should have been required to prove that petitioner knew of the features of his AR-15 that brought it within the scope of the Act.17
We emphasize that our holding is a narrow one. As in our prior cases, our reasoning depends upon a commonsense evaluation of the nature of the particular device or substance Congress has subjected to regulation and the expectations that individuals may legitimately have in dealing with the regulated items. In addition, we think that the penalty attached to § 5861(d) suggests that Congress did not intend to eliminate a mens rea requirement for violation of the section. As we noted in Morissette: "Neither this Court nor,
17 In reaching our conclusion, we find it unnecessary to rely on the rule of lenity, under which an ambiguous criminal statute is to be construed in favor of the accused. That maxim of construction "is reserved for cases where, '[a]fter "seiz[ing] every thing from which aid can be derived," ' the Court is 'left with an ambiguous statute.' " Smith v. United States, 508 U. S. 223, 239 (1993) (quoting United States v. Bass, 404 U. S. 336, 347 (1971), in turn quoting United States v. Fisher, 2 Cranch 358, 386 (1805)). See also United States v. R. L. C., 503 U. S. 291, 311 (1992) (Thomas, J., concurring in part and concurring in judgment); Chapman v. United States, 500 U. S. 453, 463 (1991) (rule of lenity inapplicable unless there is a " 'grievous ambiguity or uncertainty' " in the statute). Here, the background rule of the common law favoring mens rea and the substantial body of precedent we have developed construing statutes that do not specify a mental element provide considerable interpretive tools from which we can "seize aid," and they do not leave us with the ultimate impression that § 5861(d) is "grievous[ly]" ambiguous. Certainly, we have not concluded in the past that statutes silent with respect to mens rea are ambiguous. See, e. g., United States v. Balint, 258 U. S. 250 (1922).
619
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