Defence Of Honest And Reasonable Mistake Of Fact

, Defence Of Honest And Reasonable Mistake Of Fact

Defence Of Honest And Reasonable Mistake Of Fact

We have often heard the phrase, “ignorance of the law”. As lawyers we know that the law does not protect the ignorant. However, did you know that it is a full defence at law if you can satisfy that you held an honest and reasonable mistaken belief of fact?

Often it is difficult to differentiate between reasonable mistake of fact and law as they are generally intertwined. For example, take a person who was driving whilst unaware that he or she was suspended from driving and as a result, drove whilst suspended? Is it open to him to defend the matter?

The above example is squarely analogous to the person who was caught with drugs in his system and claimed that he didn’t know the drug was in his system as a government website suggested that marijuana only stays in the system for 12 hours. He was caught some 2 days after smoking marijuana. To read more about this, please click here.


Honest and reasonable mistake of fact is a defence which applies to strict liability offences, which do not require proof of fault, negligence or criminal intent. These types of offences do not require the prosecution to prove that an accused person intended to commit the crime.


In a well-known case dealing with the defence of reasonable mistake of fact – CTM v The Queen [2008] HCA 25 – the appellant was convicted by a jury of an offence under Section 66C(3) of the Crimes Act 1900. The offence was sexual intercourse with a person of or above the age of 14 and under the age of 16 years. The appellant reported to the police that he was convinced that the complainant was in fact 16 years old. The appeal raised a significant question of law. The question was whether or not the defence of honest and reasonable mistake of fact applied to the newly created offence under s 66C(3).

In that case, the appellant failed to discharge the burden of evidence. He was not prevented from raising the mistaken belief despite denying that sexual intercourse took place, however, there was nothing to support the honesty and reasonableness of the asserted belief that the complainant was 16 years of age. The appellant gave no sworn evidence about his belief and the complainant was not asked to respond to the appellant’s assertion in his interview with police that she had told him she was 16.


It is a basic common law principle of criminal responsibility that the accused is not criminally liable for an act or omission if he or she has an honest and reasonable belief in a state of facts, which, if it was true, would make the act or omission innocent. The term “innocent” as used here means not guilty of a criminal offence.

This kind of mistake is made when a person (the accused) has committed an offence holding an honest belief that is reasonable but mistaken.


The defence of honest and reasonable mistake of fact is based on the idea that if an honest and reasonable mistake of fact as to a particular state of affairs actually existed, then no criminal offence was committed. Consequently, the accused is not held liable for the offence.


When raising this defence in evidence, you must be able to show that you held an honest and reasonable belief that facts existed which, had they actually existed, would have meant you were not committing an offence.

The test as to whether the belief you held was honestly held is a subjective one. The test as to whether the belief was reasonable in the circumstances is an objective test.


  1. First, you must be able to prove that you honestly held the belief in the mistaken facts.

In the example referred to above, this element is satisfied, if you are charged with Driving Whilst Suspended, but were not aware that your licence had been suspended because you had not received the notification from the Roads and Maritime Services.

  1. Second, the belief forming the basis of the mistake must have been reasonable in the circumstances of your case.

In order to assess what is ‘reasonable’ in the circumstances, the court will apply the so-called reasonable person test, by asking whether an ordinary person in the same circumstances as yours would have held the same belief or acted in the same way.

  1. Thirdly, the mistake must relate to fact rather than law.

You will not be able to an argue honest and reasonable mistake based on the fact that you did not know that what you were doing was illegal. The belief you held must relate to the facts of the offence.

You must also be able to prove that if your belief had been correct, you would not have been committing an offence.

Thus, to use another ‘driving’ example, if the speedometer in your car was not calibrated correctly and you were charged with exceeding the speed limit, you could argue an honest and reasonable mistake of fact as you relied on the faulty speedometer, honestly believing that it was accurate, and if the speedometer had been correct, you would not have committed the offence.

To view our previous blogs, please click here.

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