Mistake

Despite these problems in distinguishing mistakes of law that can exculpate from the mistakes of law that do not, the modern approach possesses the key to their solution. For the modern approach says that: (1) mistakes exculpate when they negate the mens rea required by the legislature; and (2) the legislature will be presumed not to require knowledge of the existence or meaning of the criminal law. If we put aside (2) and look at (1), we can avoid the problems of classification by asking what mental states with regard to what things did the legislature require. If, for example, the legislature requires knowledge of an element, then regardless how the defendant's mistake regarding that element is classified (reasonable or unreasonable), the mistake entails that she is not criminally liable.

This solution—the analytic solution—works so long as the legislature has been relatively clear about what mental states are required for various elements. But if the legislature has not been clear, and its intent must be interpreted through recourse to more basic policies and principles, matters become difficult. For example, ignorance of different aspects of the law will reveal varying degrees of culpability. The fact that one does not know it is illegal to take what belongs to another may not diminish one's culpability one whit, whereas the fact that one does not know that the paneling he installs in his apartment is the property of one's landlord does reduce or eliminate one's culpability for later destroying it. But the degree to which culpability is reduced by legal mistakes does not provide a fine enough instrument for separating those mistakes into two categories. There are countless criminal statutes, ignorance of which is widespread, and violation of which as a result of such ignorance is surely nonculpable. And there are many mistakes regarding civil law matters that, if they result in criminal violations, would not lead us to deem those violations nonculpable. (Consider someone who, in being prosecuted for fraud, claims he did not know that lying about the existence of the item promised was lying about a material term of the contract, the materiality of the lie being a component of criminal fraud.)

The only other consideration that might conceivably assist the individuation of law required when the legislature has been silent about mens rea is the claim, frequently voiced, that the criminal law cannot as a conceptual matter require mens rea as to its own existence. However, this argument is unsound. There is nothing in the least bit paradoxical about the law's being self-referential, especially if we separate the conduct that is proscribed from the mental state accompanying it. Indeed, as proof that requiring one to be aware of a criminal statute is an entirely possible condition for holding him liable under the statute, there are actual cases, such as Ratzlaf v. United States, 510 U.S. 135 (1994), interpreting criminal statutes to make awareness of their existence a necessary condition for violation.

A third policy that might aid in the individuation of mistakes of law required under the Model Penal Code and like approaches when the legislature is silent about mental state is that of not encouraging ignorance of law, which some believe allowing mistakes of law to exculpate would do. Now while it is true in some sense that we do not wish to encourage ignorance of law, it is also true that we do not realistically expect, nor do we wish to encourage, encyclopedic knowledge of law, even criminal law (to the extent it can be separated from law generally). It would be crazily obsessive even to want judges and lawyers to possess such encyclopedic knowledge, much less the general population. Indeed, one who attains such knowledge is more likely culpable for having done so at the expense of more pressing concerns than is one who in ignorance runs afoul of some recondite legal requirement.

To summarize, the law of exculpatory mistakes distinguishes between mistakes regarding the existence and meaning of the criminal laws themselves and other mistakes of both law and fact. Although the treatment of all mistakes in either category is controlled by the legislature's specification of mens rea, when the legislature has been silent or ambiguous regarding mens rea, the distinction between these categories of mistakes becomes important in interpreting the required mens rea. However, any line that can be drawn to separate these categories appears quite arbitrary: laws are constituted by facts, and the line between the criminal law and the rest of the law can be drawn at an indefinite number of places. Moreover, the principles and policies that might rescue us from arbitrariness in drawing such lines—for example, culpability concerns and concerns with not encouraging ignorance—fail to track any consistent boundary line that might be drawn.