Impossibility Defense in Criminal Law
A defense to criminal attempt liability. Impossibility may be either factual or legal. Factual impossibility arises if the defendant has a criminal objective, but a fact or circumstance unknown to the defendant would prevent the defendant from completing the target offense. True legal impossibility arises if the defendant's completed act would not have been a crime even if the circumstances were as the defendant believed them to be. A type of hybrid legal impossibility bars liability if the defendant made a factual mistake about the legal status of some necessary element of the crime, i.e., if the defendant would have committed a crime if the circumstances had been as the defendant believed them to be. True legal impossibility may be a viable defense to attempt liability, but neither factual impossibility nor hybrid legal impossibility is an acceptable defense in most jurisdictions.