Mistake of Law

Mistake of Law: ∆'s ignorance or misunderstanding of the criminal law is generally no defense.

  • General Rule (CL & MPC): ignorantia legis neminem excusat—ignorance of the law excuses no one.
  • Narrow Exceptions:
    • Reasonable reliance on an official statement of law (statute later overturned, official interpretation, judicial decision).
    • The statute itself makes knowledge of illegality an element (e.g., some tax-code provisions).
    • Mistake of law that negates a specific-intent element (e.g., believing the property is yours in a theft case—blurs into mistake of fact).
  • MPC § 2.04(3): belief that conduct is not criminal is a defense if the law was not known and not reasonably made available, or if ∆ reasonably relied on an official statement later determined to be invalid.

Cf. Mistake of Fact — different rules apply.