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Cite as: 524 U. S. 184 (1998)

203

Scalia, J., dissenting

a license), I see no principled way to determine what law the
defendant must be conscious of violating. See, e. g., Lewis
v. United States, 523 U. S. 155, 174–175 (1998) (Scalia, J.,
concurring in judgment) (pointing out a similar interpretive
problem potentially raised by the Assimilative Crimes Act).
Congress is free, of course, to make criminal liability under
one statute turn on knowledge of another, to use its ﬁrearms
dealer statutes to encourage compliance with New York
City’s tax collection efforts, and to put judges and juries
through the kind of mental gymnastics described above.
But these are strange results, and I would not lightly assume
that Congress intended to make liability under a federal
criminal statute depend so heavily upon the vagaries of local
law—particularly local law dealing with completely unre-
lated subjects.
If we must have a presumption in cases like
this one, I think it would be more reasonable to presume
that, when Congress makes ignorance of the law a defense
to a criminal prohibition, it ordinarily means ignorance of
the unlawfulness of the speciﬁc conduct punished by that
criminal prohibition.

That is the meaning we have given the word “willfully” in
other contexts where we have concluded it requires knowl-
edge of the law. See, e. g., Ratzlaf, supra, at 149 (“To con-
vict Ratzlaf of the crime with which he was charged, . . . the
jury had to ﬁnd he knew the structuring in which he engaged
was unlawful”); Cheek v. United States, 498 U. S. 192, 201
(1991) (“[T]he standard for the statutory willfulness require-
ment is the ‘voluntary, intentional violation of a known legal
duty.’ . . . [T]he issue is whether the defendant knew of the
duty purportedly imposed by the provision of the statute or
regulation he is accused of violating”). The Court explains
these cases on the ground that they involved “highly techni-
cal statutes that presented the danger of ensnaring individu-
als engaged in apparently innocent conduct.” Ante, at 194.
That is no explanation at all. The complexity of the tax
and currency laws may explain why the Court interpreted