The Defence of Impossibility in Victoria: When Is It a Complete Defence?

The defence of impossibility is a principle in criminal law that can relieve an accused person of criminal responsibility where it was genuinely impossible for them to commit the alleged offence. In Victoria and across Australia, this concept most commonly arises where the prosecution cannot prove an essential element of the offence because the facts make the crime incapable of being committed by the accused.

Although the courts have not fully recognised impossibility as a standalone, general defence in every context, it frequently operates in practice by exposing weaknesses in the prosecution case. This article explains how the defence of impossibility works, the difference between factual and legal impossibility, its interaction with attempt offences under the Crimes Act 1958 (Vic), and how it may apply in real-world situations.

What Is the Defence of Impossibility?

In simple terms, impossibility applies where:

• It was physically impossible for the accused to commit the crime; or
• It was factually or legally impossible for the offence to occur in the way alleged.

If established, impossibility can operate as a complete defence, resulting in an acquittal. In many cases, however, the defence is raised by demonstrating that the prosecution cannot prove one or more essential elements of the offence beyond reasonable doubt.

Types of Impossibility in Criminal Law

1. Factual Impossibility

Factual impossibility arises where, due to the facts of the situation, the accused could not have committed the offence.

Common examples include:

• Alibi: The accused was not present at the scene when the crime occurred.
• Physical incapacity: A medical condition or disability made it impossible to perform the alleged act.
• Incorrect assumptions about facts: The accused believed something was illegal (for example, believing they possessed a prohibited drug), but testing later reveals it was not prohibited at all.
  
  

In alibi cases, Victorian criminal procedure requires that the defence notify the prosecution in advance, providing details of the alibi so it can be investigated. Failure to give proper notice may limit how the alibi can be used at trial.

Factual impossibility often overlaps with reasonable doubt. If the accused can produce credible travel records, medical evidence, or other documentation showing they could not have committed the offence, the prosecution’s case may collapse.

2. Legal Impossibility

Legal impossibility occurs when the act alleged, even if fully carried out, would not amount to a criminal offence.

For example:

• A person is charged with receiving stolen property, but the property was never stolen.
• A person believes they are breaching the law, but the conduct is not actually prohibited.

In such cases, the accused cannot be convicted because a fundamental element of the offence is missing.

Impossibility and Legal Duties

Impossibility can also arise where a person is under a legal duty to act but is unaware of the circumstances triggering that duty.

For instance:

• A driver is under a duty to stop and render assistance after an accident.
• If the driver genuinely does not know an accident occurred, it may be impossible for them to comply with the duty.

However, in many such cases, the more appropriate defence may be an honest and reasonable mistake of fact, rather than strict impossibility. Courts tend to analyse whether the accused had the necessary knowledge or intention required by the offence.

Impossibility and Criminal Attempts in Victoria

The law becomes more complex when dealing with attempt offences.

Under section 321(3) of the Crimes Act 1958 (Vic), a person may still be guilty of attempting to commit an offence even if unknown facts made the offence impossible to complete.

For example:

• A person attempts to pick an empty pocket, believing money is inside.
• A person attempts to receive property they believe is stolen, but it is not.

In such cases, the impossibility of completing the offence does not automatically excuse criminal liability for attempt.

Impossibility as a Mitigating Factor

Even where impossibility does not provide a complete defence, it may be relevant at sentencing.

Victorian courts have recognised that the seriousness of the attempted offence, and the realistic likelihood of success are relevant when determining penalty. 

Impossibility and Failure to Prove an Element

In practice, the defence of impossibility frequently operates by challenging whether the prosecution has proven all required elements.

For example:

• If the prosecution must prove “loitering,” but the accused’s conduct does not legally amount to loitering, the charge cannot succeed.
• If the prosecution alleges possession of a prohibited substance, but testing confirms it is not prohibited, the essential element of possession of a drug of dependence is absent.

In such cases, the court does not necessarily label the outcome as “impossibility,” but the reasoning reflects the same principle: the offence could not have been committed as alleged.

Is Impossibility a Recognised General Defence?

Australian courts have not definitively endorsed impossibility as a broad, standalone defence applicable in all situations. Instead, the concept tends to operate through:

• Failure to prove essential elements;
• Absence of intention or knowledge;
• Honest and reasonable mistake of fact;
• The statutory framework governing attempts.

As a result, whether impossibility applies depends heavily on:

• The wording of the offence provision;
• The mental elements required;
• The surrounding factual circumstances.

When Can the Defence of Impossibility Succeed?

Impossibility may succeed where:

• The accused was demonstrably elsewhere at the time of the offence (alibi).
• Physical or medical evidence makes commission of the offence impossible.
• The alleged “criminal” conduct was not illegal in law.
• A legal duty could not arise because the triggering circumstance was unknown and unprovable.
• The prosecution cannot prove a required element beyond reasonable doubt.

Key Takeaways: Defence of Impossibility in Victoria

• The defence of impossibility can operate as a complete defence in certain circumstances.
• It most commonly applies where the accused could not physically or legally commit the offence.
• In attempt offences under the Crimes Act 1958 (Vic), impossibility may not prevent liability.
• Courts may consider impossibility as a mitigating factor in sentencing.
• Often, the defence works by demonstrating that the prosecution cannot prove one essential element of the offence.

The defence of impossibility is a nuanced area of Victorian criminal law. While not always described as a separate defence, it can be decisive where the facts make the alleged offence incapable of being committed.

Every case turns on its specific circumstances, the wording of the relevant legislation, and the available evidence. If you are facing criminal charges and believe it was impossible for you to have committed the offence, obtaining early legal advice is critical to properly assess whether this defence, or another more appropriate defence, may apply.

For more information, read our blog article on impossibility defence.