The Supreme Court handed down some interesting cases this morning, and one that caught my eye involves a criminal law issue: When the law says that it’s a crime to knowingly do something, and that something has a legal status, is there a requirement that the person knows about the legal status?

The issue arose in McFadden v. United States, which involves a law banning distribution of a controlled substance. Here’s the question: Is that law violated if a person knows that he distributes a particular substance, but he does not know that that the law has designated that substance a “controlled” substance? Or is the law violated only if the person knows that the relevant legal decisionmaker has designated the substance “controlled”? The majority opinion by Justice Thomas, joined by seven other Justices, says that mere knowledge that he distributed that particular substance is enough:

The knowledge requirement may . . . be met by showing that the defendant knew the identity of the substance he possessed. Take, for example, a defendant who knows he is distributing heroin but does not know that heroin is listed on the schedules, 21 CFR §1308.11 (2014). Because ignorance of the law is typically no defense to criminal prosecution, Bryan v. United States, 524 U. S. 184, 196 (1998), this defendant would also be guilty of knowingly distributing “a controlled substance.”

Chief Justice Roberts was less sure of this. In a separate opinion, he argued that knowledge that the substance is controlled under the law may be required:

As the Court points out, the word “knowingly” applies “not just to the statute’s verbs, but also to the object of those verbs—‘a controlled substance.’” That suggests that a defendant needs to know more than the identity of the substance; he needs to know that the substance is controlled.

In cases involving well-known drugs such as heroin, a defendant’s knowledge of the identity of the substance can be compelling evidence that he knows the substance is controlled. But that is not necessarily true for lesser known drugs. A pop quiz for any reader who doubts the point: Two drugs—dextromethorphan and hydrocodone—are both used as cough suppressants. They are also both used as recreational drugs. Which one is a controlled substance?* [FN*: The answer is hydrocodone.]

The Court says that knowledge of the substance’s identity suffices because “ignorance of the law is typically no defense to criminal prosecution.” Ante, at 5. I agree that is “typically” true. But when “there is a legal element in the definition of the offense,” a person’s lack of knowledge regarding that legal element can be a defense. Liparota v. United States, 471 U. S. 419, 425, n. 9 (1985). And here, there is arguably a legal element in Section 841(a)(1)— that the substance be “controlled.”

The analogy the Court drew in Liparota was to a charge of receipt of stolen property: It is no defense that the defendant did not know such receipt was illegal, but it is a defense that he did not know the property was stolen. Here, the argument goes, it is no defense that a defendant did not know it was illegal to possess a controlled substance, but it is a defense that he did not know the substance was controlled.

Ultimately, the Court’s statements on this issue are not necessary to its conclusion that the District Court’s jury instructions “did not fully convey the mental state required by the Analogue Act.” Ante, at 10. Those statements should therefore not be regarded as controlling if the issue arises in a future case.

I’m particularly interested in this issue because a closely related question comes up when interpreting the Computer Fraud and Abuse Act. The CFAA prohibits “intentionally access[ing] a computer without authorization,” and the word “intentionally” applies to the “without authorization” element. So you run into the same interpretive problem that you have in McFadden. You could read that as saying that the government must prove intent to do a specific thing that it turns out the law says is unauthorized, much like the majority reads the statute in McFadden. Alternatively, you could say that the government has to prove that the defendant knew that his act was unauthorized under the law and that he intentionally did that thing, akin to the Chief’s approach.

In the CFAA context, my understanding has always been that the former reading — like the McFadden majority — is more persuasive. As the majority suggests, the norm in federal criminal law is that knowledge of illegality is irrelevant. Congress knows how to make subjective awareness of illegality an element: They use the willful mental state for that. See Cheek v. United States, 498 U.S. 192 (1991). So I’d be reluctant to adopt the latter reading, as I fear it amounts to reading the word “intentionally” as if it said “willfully.” And although there have been no appellate decisions on the question, this is the interpretation that trial courts have adopted for purposes of jury instructions.

With that said, the question gets trickier as you vary the role of the element with respect to the overall offense. The more the element is the core of the crime, the more it seems like the norm that ignorance of the law is no excuse should apply. On the other hand, the more the legal question raised by the element is distinct from the definition of the crime, the more it seems like knowledge of a legal status can be incorporated without running afoul of that principle. And from a policy perspective, the more cases of fair uncertainty as to legality you have, the more desirable it becomes to incorporate knowledge of illegality as an element. That surely has an influence on interpretation, even if is not directly relevant doctrinally. Either way, very interesting questions.