Mistake of Fact/Mistake of Law vs. Legal Impossibility/FactualImpossibility

The following question was asked in a comment on the blog:

"Hi Sean, can you discuss mistake of law, fact, factual impossibility, and legal impossibility, as well as voluntary intoxication, and when they are relevant as defenses to crimes, or to negate mens rea? "

Response:

This is an area of Criminal Law that, under time constraints on the MBE, could cause some trouble. I think it's best to go through each individual area, noting the distinctions.

Mistake of Fact: Mistake of fact is implicated only if the facts provided show that the defendant lacked the state of mind required for the crime. Because strict liability crimes do not take into account the state of mind of the defendant, mistake of fact is not a valid defense to strict liability crimes (such as statutory rape). You do, however, need to distinguish between specific intent crimes, and general intent crimes, when analyzing mistake of fact. If mistake of fact is offered as a defense to a specific intent crime, the mistake need not have been reasonable, but if it is offered as a defense to a general intent crime, it has to have been reasonable for it to be a valid defense to the crime. On that note, one of the initial considerations when studying Criminal Law should be to distinguish between specific intent crimes and general intent crimes.

Mistake of Law: Unlike with mistake of fact above, it is generally not a valid defense that the defendant believed that his activity would not be a crime, even if that belief was reasonable, and even if that belief was based on the advice of his attorney. However, an exception on the MBE that you should especially look out for is where a statute proscribing the conduct that the defendant engaged in was not published or made reasonably available prior to the conduct constituting the crime for which defendant has been charged.

Factual Impossibility: Factual Impossibility arises only when it would be factually impossible for the defendant to complete the crime. Like mistake of law, above, it is rarely a valid defense. An example is X entering a store with the intent of shooting and killing Y, and then stealing property. It may be the case that it would have been impossible for X to shoot and kill Y because the gun, unknown to X, was not loaded. This factual impossibility, however, will not prevent X from being charged with attempted murder, if the other elements of attempt are satisfied.

Legal Impossibility: Legal impossibility arises when the defendant did, or intended to do, acts that would not constitute a crime under any circumstances. In other words it is legally impossible for those acts to have been a crime. Even if defendant believed that his acts constituted a crime, he can be charged with no crime for engaging in those acts if, objectively, he was committing no crime. All states (and the Model Penal Code) recognize this defense.

Intoxication: Intoxication should be analyzed by determining whether the defense is being offered as a defense to a specific intent crime, or a general intent crime. Voluntary intoxication is a valid defense to specific intent crimes, unless the defendant voluntarily became intoxicated for the sole purpose of establishing the defense. It is not a valid defense to general intent crimes, or strict liability crimes. Involuntary intoxication will be treated as a mental illness (and if it rises to the level of insanity will be a valid defense against all crimes), if the substance causing the intoxication was taken without defendant's knowledge, under duress, or pursuant to medical advice while defendant was unaware of the intoxicating effects.