Introduction

Mistake of Law Defenses

Introduction

A person who has been assured by a government office that an activity is lawful, and who is later prosecuted for doing it, has a grievance that sounds close to unanswerable. So does a person who simply believed, with no assurance from anyone, that the conduct was permitted. Whether either can defend on the strength of that belief depends on a baseline rule that is firmly against them. Under both the common law and the Model Penal Code, ignorance of the law is no excuse, and a defendant ordinarily cannot escape liability by claiming not to have known that the conduct was unlawful.¹ The Code builds this baseline into its definition of culpability: knowledge that conduct is an offense, or knowledge of the law that defines the offense, is not part of the mental element unless the statute clearly requires it.² The reason is one of incentive. If a sincere belief in lawfulness excused conduct, every person would gain by never learning the law, and a legislature that wants citizens to find out what is forbidden and obey it would end up rewarding the opposite habit.³

Against that baseline, Model Penal Code § 2.04 is the Code's home provision on ignorance or mistake, and its subsection (3) carves out one narrow exception.⁴ The governing text provides that a "belief that conduct does not legally constitute an offense is a defense to a prosecution for that offense based upon such conduct" in two situations.⁵ The first door opens when the statute or other enactment defining the offense was not known to the actor and had not been published or otherwise reasonably made available before the conduct. The second opens when the actor reasonably relied on an official statement of the law, found in one of four listed official sources and afterward determined to be invalid or erroneous.⁶ Both doors answer the same worry, which is the apparent unfairness of convicting a person who had no fair notice that the conduct was illegal.⁷ In the first, the law was unavailable, so even a diligent person could not have learned it. In the second, the state's own official voice pointed the wrong way, so punishing the conduct would penalize the person for trusting the government. Because the excuse arises only where the failure of notice traces to the state, it leaves the incentive behind the baseline rule largely intact: a person who simply did not bother to look up the law gains nothing from it.

This reading concerns only that notice-based excuse. A mistake that prevents the prosecution from proving the purpose, knowledge, belief, recklessness, or negligence that a material element requires follows a different path under § 2.04(1), and a neighboring reading covers it.⁸ Subsection (3) asks instead whether the legal system gave the defendant a fair chance to know that the conduct was forbidden, and subsection (4) places the burden of proving the defense on the defendant by a preponderance of the evidence.⁹ This chapter follows the Code's order: the baseline first, then each door and the limits that keep the reliance defense narrow, then the rules for proving the defense and the constitutional protection that backstops it. The next section begins with the no-excuse rule and the reasons courts give for it.