The impossibility defense can only be applied for incomplete offenses (i.e. attempt). There are two types of impossibility defenses: factual impossibility and legal impossibility.
- Factual Impossibility – the defendant could not complete the crime because…; this defense seeks to negate the actus reus. The defendant is arguing that something got in the way of his completion of the crime. Generally, a factual impossibility defense is not permitted.
- Legal Impossibility – even if the defendant’s conduct was or is completed, it is not illegal. Here, the court looks at the elements of the offense and finds that not all of the elements are present. Even if the defendant thought his conduct was wrong, a legal impossibility defense will be valid.
Example: Defendant burns down his own house in order to collect the insurance proceeds. Under common law, arson required the burning of the dwelling of another. Therefore, it is legally impossible to find the defendant guilty of arson.