When facing criminal charges in California, one of the most powerful—yet often misunderstood—legal defenses is the Mistake of Fact defense. It can mean the difference between a conviction and a complete dismissal of charges, but it only applies under very specific circumstances.
Imagine being arrested for theft after picking up the wrong phone at a café, truly believing it was yours. Or being accused of assault because you struck someone you mistakenly thought was attacking you. In both examples, your intent plays a critical role—and that’s where the Mistake of Fact defense comes in. Whether you’re a defendant, law student, or just curious about criminal law, this guide offers clear, actionable insight into one of California’s most nuanced defenses.
1. Understanding “Mistake of Fact” as a Legal Concept
A mistake of fact occurs when a person has an incorrect belief about a fact that’s relevant to a criminal charge. In California, this can matter because guilt often hinges on whatever mental state—mens rea—a law requires. For example:
If you took someone else’s property thinking it was your own, you might lack the intent needed for theft.
Likewise, if you used force thinking you were in danger, you may lack the intent required for assault or battery.
Why it matters: Criminal convictions usually need two elements:
A prohibited act (actus reus)
A criminal intent (mens rea)
If a person honestly and reasonably misunderstood a fact central to intent, California law sometimes lets that person avoid conviction—even if the mistake later proves incorrect.
2. Statutory Basis: California Penal Code § 26(1)
California’s statutory framework spells it out: “All persons are capable of committing crimes except those who commit the act or make theomisison charged without being aware of the facts which make the act or omission criminal…” – Penal Code Section 26, subdivision 1.
This means if someone isn’t aware of essential facts that make their act unlawful, they generally can’t be held criminally responsible.
3. Types of Mistakes of Fact
| Type | Definition | Example |
|---|---|---|
| Reasonable (Honest & Good-Faith) | The belief is both honest and one that a reasonable person might hold. | Picking up someone else’s phone, believing it’s yours. |
| Honest but Unreasonable | The belief is sincere, but no reasonable person would have it. | Thinking it’s okay to punch someone who’s barking at your dog. Generally not valid. |
| Honest with Mixed Motives | The belief exists, but mixed with ulterior motives (e.g., to benefit unlawfully). | Claiming you wrongly believed another’s car was yours but intended to “borrow” it anyway. |
4. Criminal vs. Non-Criminal Acts
Criminal Offenses: E.g., theft, assault, rape
Require proof of intent. Mistake of fact defense works if it negates intent.
Strict Liability Crimes: E.g., statutory rape, some traffic offenses
Often don’t require intent; even honest mistakes aren’t a valid defense unless the law explicitly allows them.
Regulatory (Public Welfare) Offenses
Also often allow no-fault prosecution, and reasonable mistakes might not help.
5. Key California Court Cases
People v. Concha (2001)
A sneezing and upset stomach by Concha caused a motel employee to believe he was intoxicated. Courts ruled that a reasonable mistake (in remembering the event) could negate intent to commit a misdemeanor.
People v. Dekraai (2016)
The defendant believed a divorce attorney was interfering with his custody case and acted upon that belief. The court acknowledged even problematic beliefs might affect mens rea, but limits apply if beliefs are unreasonable.
People v. Lee Kong (1897)
A classic case: man took another’s horse believing it was his—an honest and reasonable mistake, so theft charges didn’t stick.
These cases show courts weigh whether a mistake was genuine, reasonable, and directly related to the mental state required for the crime charged.
6. When the Defense Can Succeed
To use mistake of fact as a defense in California:
Statutory requirement: The underlying crime must include a mental-state element (e.g., intent, knowledge).
Honest belief: The defendant must have genuinely believed in the mistaken fact.
Reasonableness: The belief must be what a reasonable person in the same circumstances would have thought.
Timing: The belief must exist at the moment the alleged crime was committed—even if it’s short‑lived.
7. Examples
A. Theft Offense
Facts: You take a phone from a table in a coffee shop, thinking it’s yours.
Application: Honest belief. If someone in your shoes could reasonably make the same error, you may lack intent—making the defense valid.
B. Assault or Battery
Facts: You punch someone thinking they’re about to hit you.
Application: Honest & reasonable fear removes intent to commit assault. You’d face an issue-centered around justifiable self-defense as well.
C. Rape/Unlawful Sexual Intercourse
Facts: You reasonably believe your partner consented.
Application: In California, the law used to allow a reasonable mistake of fact defense (even if mistaken), but Proposition 8 passed in 2020 removing the belief-in-consent defense entirely. You may be ineligible to use it now.
8. Statutory Exceptions & Limitations
Prop 8 (2020): Eliminated criminal defense for “mistake of fact about consent.” Even a reasonable, honest belief does not excuse sexual assault/rape in California.
Strict Liability Crimes: Because there’s no mens rea component, an honest mistake does not generally excuse the conduct.
Confusion vs. Mistake: Simple confusion (“I forgot”) is different from a genuine mistaken belief.
9. Jury Instructions & Burden of Proof
In California criminal trials:
If the defense raises the issue of a reasonable mistake of fact, courts must give CALCRIM 3406 or similar instructions.
The defendant must present some evidence for honest & reasonable belief.
Once there’s evidence, the prosecution must prove beyond a reasonable doubt that the defendant did not hold that belief.
10. Practical Tips For Defendants & Attorneys
Document your belief, if possible — e.g., signed notes, timelines, witness testimonies from the moment.
Compare your belief against standard of reasonableness.
In sexual-offense charges, don’t rely on mistake of fact regarding consent—Proposition 8 closed that path.
Some crimes—like defrauding an older adult—involve legal impossibility, which confers no defense.
11. Difference Between Mistake of Fact and Mistake of Law
Mistake of Fact: Wrong about a circumstance (e.g., property owner, consent). In some cases, a valid defense.
Mistake of Law: Wrong about what the law says. Generally not a valid defense—“ignorance of the law is no excuse”—except for certain limited situations.
12. FAQs
Q: Can I claim mistake of fact if I genuinely thought I had permission?
A: Yes—if your belief was reasonable under the circumstances. If you acted recklessly or vaguely guessed, the defense likely won’t hold.
Q: Does not understanding a law count as a mistake of fact?
A: No. That’s mistake of law, and ignorance—even honest—is typically no defense.
Q: Does mistake of fact work for speeding tickets?
A: Usually not. Traffic offenses are typically strict liability; a genuine but unreasonable belief (e.g., you “thought” there was a 65‑mph limit in a school zone) isn’t an excuse.
Concluding Takeaways
When it works: If the crime hinges on intent (like theft or assault), and you honestly and reasonably misunderstood a key detail, the defense might succeed.
When it doesn’t: For strict liability offenses, regulatory crimes, or rape cases post‑Prop 8, you generally can’t use it.
How to prepare: Keep clear documentation, focus on your genuine belief and its reasonableness, and ensure your attorney seeks proper jury instructions.
Encouragement to Seek Professional Help
If you or someone you know is facing criminal charges in California, understanding whether a mistake of fact defense applies is critical—and the nuances are complex. You should consult an experienced criminal defense attorney promptly. They can:
Review your case in detail
Gather supporting evidence or testimony
Request the proper jury instructions
Navigate tricky areas—like Prop 8’s exceptions—for you
Additional Resources
California Jury Instructions (CALCRIM 3406) – Model instruction on mistake of fact
Summary
The mistake of fact defense in California criminal law is powerful—but narrow. It operates only where intent matters and only when your belief is both honest and reasonable. You cannot use it in strict liability crimes or sexual assault cases post‑Proposition 8. Courts carefully scrutinize whether your belief fits what a “reasonable person” would genuinely hold under the same circumstances. If successfully established, it can negate criminal intent and lead to acquittal.
