Under the MPC, which statement best describes the effect of reasonable mistake?

• A. Not a defense
• B. Mitigates offense
• C. Always a complete defense
• D. MPC & NY: not a defense

Answer: (C)

Reasonable mistake of fact can negate the required mental state for the crime, and under the MPC that negation means there’s no liability for the offense. Liability under the MPC hinges on having the culpable mental state for each element of a crime. When the facts as the defendant reasonably believed them would negate that mental state, the charged conduct isn’t criminal in the eyes of the statute. Because the essential element—the culpable mental state—disappears due to a reasonable belief about the facts, the result is acquittal rather than merely a lesser penalty. This is why, for offenses that rely on a specific mental state, a reasonable mistake can serve as a complete defense. (Note this doesn’t apply to strict liability offenses that don’t require any mental state. New York follows the same general principle.)