Legal impossibility is a traditional common law defense to a charge of an attempted crime. Legal impossibility arises when the act, if completed, would not be a crime. A person believes she is committing a crime, but the act is, in fact, lawful. For example, a person may believe she is receiving stolen goods, but the goods are in fact not stolen.
A different form of legal impossibility (Known as "hybrid legal impossibility") comes into play when an actor's goal is illegal, but commission of the crime is impossible due to a factual mistake regarding the legal status of one of the attendant circumstances of one of the elements of the crime. For example, a man attempting to bribe someone whom he mistakenly believes is a juror is not liable for attempted bribery of a juror. On the other hand, some jurisdictions may find the actor guilty of attempt. For example, under the Model Penal Code, the defendant can be guilty of the attempted crime if the facts being the way she thought they were would indeed make it a crime; however, she would not be guilty of the completed crime, because the crime was never completed.
See also impossibility defense.