MBE Rules · Criminal Law
Mistake of fact vs. mistake of law
The rule
Mistake of fact: defense if it negates the required mens rea. Specific intent — any honest mistake. General intent — must be reasonable. Strict liability — never. Mistake of law: generally NOT a defense (ignorance is no excuse), except (1) reliance on official interpretation, (2) lack of notice for malum prohibitum offenses (rare).
In plain English
If you misunderstood a fact and it affects your intention, it might excuse you, but misunderstanding the law usually won't help unless you relied on an official statement.
Worked example
The defendant believed a jacket was theirs and took it. If this mistake was honest, it might excuse theft. But if they didn't know taking jackets was illegal, that's not a defense unless a police officer told them it was okay.
Memory hook
Fact vs. Law: Facts can free, law locks up. Mistake of fact can negate intent; mistake of law rarely helps.
The trap
Students think: Any mistake can be a defense. Wrong, because mistake of law almost never works. The actual test is mistake of fact negates mens rea.
How examiners test it
MBE loves: defendant claims ignorance of the law. Trap: students assume it's a defense—it's not, unless an official told them wrong.
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