Mistake

The rule is sometimes rephrased as saying that everyone is conclusively presumed to know the law. When Blackstone wrote, such a view was at least plausible. A claim that one did not know that rape, murder, robbery, or mayhem was illegal (or immoral) would hardly be taken seriously. Yet the rule continues to be followed today, when criminal law applies to many new areas of activities and encompasses literally hundreds of thousands of administrative regulations as well.[2] If this explanation of the rule were tested against modern methods of assessing presumptions,[3] it would be clearly unconstitutional.

The argument that the claim of ignorance is too easily made and too difficult to refute was rejected by Justice Holmes, who pointed out that that concern was present for virtually all defensive claims. To the extent that it was easier to make than some of those other claims, the law could place on the defendant the burden of persuasion. O.W. Holmes, The Common Law (1881).

Holmes proffered another support for the rule, however—that we wish to encourage people to learn what the criminal law is. Moreover, as an ardent utilitarian, he argued that it is occasionally necessary to sacrifice the morally innocent person to achieve the better good of establishing an incentive for learning the law. However, the doctrine has been applied even where the defendant has actively sought legal advice from various sources, including court opinions, judges, prosecuting attorneys, and lawyers. Still, there is the problem that Selden raised: Even if Arthur at trial produces those lawyers, priests, and government officials, and they affirm their advice, how will the prosecutor ever find the 30 lawyers, priests, and officials who gave Arthur different advice? Should he put Arthur’s picture in the newspaper with the caption “If you gave this man legal advice on dumping toluene, call my office”?

Similarly unsuccessful has been the argument that, even if ignorance of the criminal law should not excuse (in order to encourage persons to learn what the criminal law is), ignorance (or mistake) as to other laws, which are then incorporated into the criminal law, should excuse.[4] Suppose the criminal law prohibits blocking public roads, and Yehudi knows that he is blocking a road but he believes the road to be private. Unknown to him, the road has become “public” under condemnation just a few hours before. Yehudi should not be punished, the argument goes, because he has learned what the criminal law prohibits. His mistake is about condemnation law, not criminal law.

Until very recently the rule has reigned virtually unchallenged. However, the Model Penal Code and several recent United States Supreme Court cases discussed below suggest that future decisions may be more open to changing the rule, at least in some contexts.