Is ignorance an allowable defense?

Mistake of Law
A few summers ago, I rented a house in Wilmington, NC with a guy from Maine. One night the cops caught him drinking in his car, and were all set to write him a ticket. Andy told them that drinking in your car was legal in Maine, as long as the engine is off. Therefore, he didn't know he was breaking the law. And they let him walk!

This is a Mistake of Law defense, and it is not valid in any court. When you engage in an activity, it’s your responsibility to know the relevant laws. Andy waived the right to live by Maine law when he moved to North Carolina for the summer. I’m sure the police knew this, but they must have felt bad for the guy.

Just in case you ever visit Maine, let me point out that Andy was probably lying about being allowed to drink in your car.

Mistake of Fact
Ignorance can only be a defense if it applies to fact patterns, and even this defense is not absolute. Imagine buying a rifle on Craigslist, only to be arrested later for possession of a stolen gun. You have a solid Mistake of Fact defense, because you honestly didn’t know the weapon was stolen.

Bear in mind that Mistake of Fact is intricately tied to mens rea (criminal intent). If the statute in your jurisdiction was "knowingly possess a stolen gun", your case is airtight. What if the statute stated "negligently possess a stolen gun", and the gun was covered in blood when you received it? You probably aren’t getting away with that one.

A bit on Strict Liability
Some acts are sufficiently wicked that strict liability comes into play, which makes the fact pattern irrelevant. For example, some states use strict liability for statutory rape. A defendant might claim that his victim told him she was 18, and that he was mistaken about her factual age. Under strict liability, he is still guilty.

We’ll delve much deeper into strict liability in the next Criminal Law post.

summarized from Life of a Law Student