Editing Mens rea (section)

== Ignorance of law contrasted with ''mens rea'' ==
The general rule under common law and statutory law is that ignorance of the law or a mistake of law is no defense to criminal prosecution. However, in some cases, courts have held that if knowledge of a law, or if intent to break a law, is a material element of an offense, then a defendant may use good faith ignorance as a defense.<ref>{{cite web |author1=Byron White |author1-link=Byron White |title=John L. CHEEK, Petitioner, v. UNITED STATES (498 U.S. 192) |url=https://www.law.cornell.edu/supremecourt/text/498/192 |website=Legal Information Institute |access-date=5 May 2022 |quote=The proliferation of statutes and regulations has sometimes made it difficult for the average citizen to know and comprehend the extent of the duties and obligations imposed by the tax laws. [...] Thus, the Court almost 60 years ago interpreted the statutory term "willfully" as used in the federal criminal tax statutes as carving out an exception to the traditional rule. This special treatment of criminal tax offenses is largely due to the complexity of the tax laws.}}</ref>

In the 1991 US Supreme Court opinion for ''[[Cheek v. United States]]'',<ref>{{cite web |author1=Byron White |author1-link=Byron White |title=John L. CHEEK, Petitioner, v. UNITED STATES (498 U.S. 192) |url=https://www.law.cornell.edu/supremecourt/text/498/192 |website=Legal Information Institute |access-date=5 May 2022}}</ref> [[Byron White]] wrote: {{blockquote|The proliferation of statutes and regulations has sometimes made it difficult for the average citizen to know and comprehend the extent of the duties and obligations imposed by the tax laws. [...] Thus, the Court almost 60 years ago interpreted the statutory term "willfully" as used in the federal criminal tax statutes as carving out an exception to the traditional rule. This special treatment of criminal tax offenses is largely due to the complexity of the tax laws.}}

Crimes like tax evasion are specific intent crimes and require intent to violate the law as an element of the offense. In ''R v. Klundert'', for example, the [[Court of Appeal for Ontario]] found as follows:

{{blockquote|[55] Section 239(1)(d) is part of an Act which is necessarily and notoriously complex. It is subject to ongoing revision. No lay person is expected to know all the complexities of the tax laws. It is accepted that people will act on the advice of professionals and that the advice will often turn on the meanings to be given to provisions in the Act that are open to various interpretations. Furthermore, it is accepted that one may legitimately structure one's affairs so as to minimize tax liability. Considered in this legislative context, I have no difficulty in holding that a mistake or ignorance as to one's liability to pay tax under the Act may negate the fault requirement in the provision, regardless of whether it is a factual mistake, a legal mistake, or a combination of both.}}

A good-faith belief that a law is unjust or unconstitutional is no excuse, but "reasonable reliance upon an official statement of law, afterward determined to be invalid or erroneous" does not constitute a criminal act.

In the United States, a law must be reasonably clear; it must be worded so that a reasonable layman can comprehend the specific prohibited acts. Otherwise, the law may be unconstitutional pursuant to the [[vagueness doctrine]].