The Defence of Honest and Reasonable Mistake (Vic) | Armstrong Legal

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This article was written by Deike Kemper - Associate - Melbourne

Deike Kemper holds a Juris Doctor (Master of Laws degree) from Monash University, a Graduate Diploma of Legal Practice from the College of Law and a Graduate Certificate of Forensic Psychology from Curtin University. She is admitted to practice in the Supreme Court of Victoria and the High Court of Australia. Deike’s main area of practice is criminal law. She...

The Defence of Honest and Reasonable Mistake (Vic)


Most criminal offences require the accused to have acted either intentionally or recklessly as to the offending conduct. However, there are a number of offences, especially under the Road Safety Act, which are ‘strict liability’ offences. This means that the state of mind of the accused when they committed the offence is irrelevant. For example, it does not matter whether the accused intended to drive whilst suspended, or whether the accused was reckless as to it, all that matters is that the accused did drive whilst their licence was suspended. For these offences, the defence of honest and reasonable mistake of fact is available.

What is honest and reasonable mistake of fact?

When an offence is a strict liability offence, the defences which are available are very limited. An accused may argue factual defences  (eg. that their licence was actually not suspended). However, the only legal defence available to strict liability offences is that the accused committed the offence as a result of an honest and reasonable mistake of fact. To succeed with this defence, the accused must show that they held an honest belief of a certain state of affairs and facts, which had they been correct would have rendered the offending act innocent. They must also show that the belief was reasonable.

An example of when a person may rely on this defence is when an accused charged with driving while suspended honestly held the reasonable belief that their licence was valid and not suspended. Whilst many persons may easily be able to argue that they had the honest belief that such was the case, the hurdle of demonstrating that the belief was reasonable is significant.

When can honest and reasonable mistake be argued?

Notably, though whilst almost all offences under the Road Safety Act are strict liability offences, there are also a number of offences under the Crimes Act, such as dealing with suspected proceeds of crime, where this defence is available.

Mistake of fact vs mistake of law

It is also important to note that the mistaken belief must be in relation to a matter of fact and not a matter of law. One cannot enliven this defence by saying it was the accused’s honest but mistaken belief that it was not illegal to drive whilst suspended. One can only enliven the defence by saying it was their honest though mistaken belief that their licence was not suspended.

To summarise, the following three elements must be proven in order to successfully rely on this defence:

  • The mistaken belief was a genuinely bona fide honest belief held by the accused at the time of the offending;
  • The mistaken belief must have been reasonable in the circumstances; and
  • The mistaken belief related to a fact, not law.

With respect to the reasonableness of the mistaken belief, arguably the hardest element to make out, it is relevant to note that the standard that applies is an objective standard. The reasonableness of the accused’s belief will be measured objectively by the observed circumstances.

Once the defence of honest and reasonable mistake is raised by an accused or their legal representatives, the onus is on the prosecution to prove, beyond a reasonable doubt that the mistaken belief was either not honestly held, not reasonably held or not a mistake of fact.

A number of key cases have considered the defence of honest and reasonable mistake. They can be summarised as follows:

  • Proudman v Dayman [1941] established that the mistaken belief must be a positive belief formed by the accused not just mere ignorance;
  • Knight v R (1992) 175 CLR 495 established that if the facts of a case allow for an inference consistent with the accused’s innocence, then the accused must be given the benefit of doubt. This applies to the consideration of this defence;
  • He Kaw Teh v The Queen [1985], established, in furtherance of Proudman v Dayman, that the accused must have expressly turned their mind to a particular fact and made the honest mistake which was reasonable in the circumstances. The accused must have done more than just not considered the matter at all.
  • Mei Ying Su and Others v Australian Fisheries Management Authority and Another (no2) (2008) confirmed at [106] that the defence:
    • does not involve the hypothetical ordinary or reasonable person test.
    • it requires that the belief be that of the accused
    • it requires that the accused’s belief be objectively reasonable, that is, rational, based on reason, or capable of sustaining belief and
    • it requires the objective reasonableness of the accused’s belief to be assessed by reference to the subjective circumstances in which the accused was placed, including the accused personal attributes and the information available to him at the time.

If you require legal advice or representation in any legal matter please contact Armstrong Legal. 

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