The defence of impossibility aims to absolve the defendant of criminal responsibility by proving that it was physically impossible for the defendant to have committed the offence.
An example of when a person might successfully raise this defence is in situations where they are not present when the crime took place. This is a situation of factual impossibility. However, the prosecution must be informed of any alibi that is raised in support of the fact so that they have the opportunity to double check the validity of the alibi.
Another category of cases where the impossibility defence is raised are cases of legal impossibility. An example of such a case would be where a person was charged with receiving stolen property, but it was later found out that the property was not stolen.
The defence is also available in situations where the defendant is under a legal duty to act in a certain way in certain circumstances. If the defendant is not aware of the circumstances, then it is impossible for them to breach their duty to have acted in the way required by the duty.
Frequently the form this defence takes is by the defence highlighting that the prosecution is unable to prove one of the elements of their case. For example, in Starri, a man who was restrained by a bouncer was not convicted for failure to cease loitering. Here, the prosecution was unable to prove that Starri's conduct amounted to 'loitering'. The courts, however, have not yet agreed on the concept of impossibility as a general defence.