human being. Everyone seems to agree that type 1 mistakes negate the intent required for commission of the offense, but if the defendant is negligent with regard to the relevant element, he or she may be guilty of negligently committing the offense.
Type Two: Mistakes about Norms of the Definition , e.g., a mistake about whether property held in joint ownership with a spouse is property "belonging to another" under the rule defining theft. These are mistakes about whether particular factual situations fall within a prohibition of the criminal law. They are not, strictly speaking, mistakes about the interpretation of the norm and therefore do not qualify as mistakes of law. They are irrelevant to liability.
Type Three: Mistakes about the Factual Basis of Justification , e.g., Bernhard Goetz believes unreasonably that someone who smiles at him is about to attack him. This is the most controversial category. My view is that these mistakes should be treated as excuses, effective only if reasonable.
Type Four: Mistakes about the Norms of Justification , e.g., the actor thinks that consent is a defense in homicide cases. These are pure mistakes of law, for which the better rule would be to excuse all reasonable, unavoidable mistakes. If the mistake is unreasonable, it is not clear that the defendant should get the benefit of his good faith views.
Type Five: Mistakes about the Factual Basis of Excuses , e.g., the actor thinks he is in great danger when he is not. These mistakes should be relevant only so far as they permit the conclusion that the defendant's wrongdoing was, all things considered, not blameworthy.
Type Six: Mistakes about the Norms Governing Excuses , e.g., the actor thinks he is entitled to rely on the advice of his lawyer about what it is legal for him to do. These mistakes should be irrelevant.
It is appropriate to end the chapter with a judgment that certain kinds of mistakes are irrelevant. Yet these are difficult and subtle matters and there is room to argue that good faith reliance on a lawyer's advice should indeed be relevant. The issues raised in this chapter are among the most difficult in the theory of the criminal law. Readers are invited to make their own contribution to the problem.