Ignorantia legis non excusat-ignorance of the law does not excuse-is a centuries-old criminal law maxim familiar to lawyer and layperson alike. Under the doctrine, an accused finds little protection in the claim "But, I did not know the law," for all are presumed either to be familiar with the law's commands or to proceed in ignorance at their own peril. The ignorant must be punished along with the knowing, the maxim teaches, to achieve a better educated and more law-abiding populace and to avoid the easy-to-assert and difficult-to-dispute claim of ignorance that would otherwise flow from the lips of any person facing criminal punishment. Despite this country's long-standing allegiance to the hoary maxim, over the last century, and in particular over the last decade, the courts have seriously eroded the ignorantia legis principle by frequently construing the mens rea term "willfully" to require proof of an accused's knowledge of the law. The erosive effect that these constructions have had on the ignorantia legis maxim is referred to in this Article as the "jurisprudence of willfulness." Professor Davies demonstrates that, contrary to the maxim, the number of federal criminal statutes that have been construed to impose such a heightened mens rea requirement is already quite large. The Article reveals that, if the courts continue to employ their current interpretive approach to the term "willfully," at least 160 additional federal statutes containing the term are at risk of similar treatment. The author argues that contemporary constructions of the troublesome scienter term to impose a knowledge of the law element have been grounded on doubtful, unchallenged logic and have bequeathed a legacy of grave interpretive confusion. Professor Davies maintains that much of the "jurisprudence of willfulness" is inimical to congressional judgments and, therefore, violative of rule of law and separation of powers principles. The Article urges a return to the ignorantia legis principle in all cases in which a clear legislative intent to abandon the maxim when employing the term "willfully" is missing.

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