Types of Criminal Defences

While trial is a complicated affair full of rules, regulations, and expected decorum, I believe that everyone has a right to know the most common defence arguments. These are used when you do not dispute the occurrence of the event(s), but rather, the circumstances of the events. Without further adieu, the following is a brief description of the defences.


If your conduct was involuntary then we can raise the defence of automatism. This means that you had no conscious control over your body’s movements. If the defence of automatism is successful, it means you lacked the necessary mens rea (mental aspect) for a conviction. There are two different kinds of automatism: (1) mental disorder, and (2) non-mental disorder. Automatism that derives from a state of temporary insanity is classified as mental disorder. It is important to know that under current case law, automatism cannot be used if you entered that state willingly. For example, if you choose to get drunk and then get into an accident, you cannot claim that you were so intoxicated as to not realise you were driving.


In certain situations, you can claim that the victim consented to your actions. For example, if two parties agree to engage in combat sports. However, under current case law, a person cannot consent to physical harm. Furthermore, consent is never a defence to murder. Another example would be if your neighbor agrees to lend you his property. That consent would be a valid defence against theft. The Crown Prosecutor would have to prove that there was an absence of consent from the property owner in order to prove your guilt.


This defence can only be used in extremely limited circumstances, as the duress needs to occur at the very moment you are committing the offense. Furthermore, to establish this defence the evidence must show that you were compelled to act by threats of immediate bodily harm, and that you believed at the time of committing the offence, that the threat would be carried out. The defence cannot be used in cases of murder, attempted murder, treason, sexual assault, forcible abduction, piracy, arson, or robbery. Finally, the person delivering the threat must be present at the time the offence was committed.


This defence can be utilized if you were ‘set-up’ or trapped into committing a crime by the police. An example of this would be an undercover police officer threatening you into buying drugs. This defence is often used for narcotics crimes and prostitution offences. This defence is one that recognizes that sometimes police can abuse the process to find/charge alleged criminals. The police can avoid this defence by investigating a target that has already engaged in crime, and they must be carrying on a genuine investigation.


While intoxication is usually not an effective defence to a criminal charge, it may be used to  alter the charge in certain circumstances. It can be used as a partial defence to specific intent crimes. These are crime which require intent in order to prove guilt. Thus, if you were too intoxicated to form the necessary intent to carry out a specific crime, then this defence can be quite effective. Once again it should be noted that if you willingly got extremely intoxicated, for the sole purpose of avoiding liability, this defence will fail. Furthermore, the bar for how intoxicated you must be is quite high. The Supreme Court of Canada stated in R. v. Perrault that the degree of drunkenness must render a person “so stupid by drink that he does not know what he is doing.


There are three factors that must be met in order for this defence to apply. You must have either a natural imbecility, a disease of the mind, or an inability to appreciate the nature and quality of an act while you were committing it:

Natural imbecility: a person’s mental development is limited, and the condition that has thus limited the person was caused at birth, or by natural decay.

A disease of the mind: This is more complicated and heavily reliant on the facts of the case. Some examples of disorder that courts have recognized in the past are schizophrenia, dementia, paranoia, and some types of epilepsy. In order for this defence to be successful, you must suffer from the impairment at the time of the offense, although it does not need to be a permanent condition.

While most of the time the Crown must prove that you had the mental aspect of the crime, in order to use this defence the onus is shifted. This means that you, the accused, must prove your state of insanity to the court, rather than the Crown proving that you were sane.

Mistake of Fact/Mistake of Law

If you believe that your actions were not criminal by virtue of the circumstances, then this defence can be highly effective if certain factors are met. The mistake must be 1) an honest one, and 2) such that no offence would have been committed if the circumstances had been as you believed them to be. For example, if you are at a party, and when you leave you take the wrong jacket (thinking it is yours), then no crime has been committed. This is because if the facts were as you thought them to be (i.e., that the jacket was yours) then no crime would have been committed.

A mistake of law, by contrast, is a very limited defence. This is mainly used if an official provides you permission to act, but the act itself is a violation of the law. For example, if a tow truck driver is asked to remove a vehicle from private property, and the vehicle is in fact owned by somebody else, the driver could not be blamed for thinking his actions are legal.

It is important to note that mere ignorance of the law is not an excuse to commit crimes. (i.e., you cannot claim that you did not know that murder was illegal)


This defence is rarely used, and essentially means that an ordinary person was compelled to break the law due to an emergency. For example, you witness a car accident, and break the car window to free a trapped victim, this defence would protect you from the damage you caused to property (the car).


While provocation is not a defence, it is a relevant condition for the use of self-defence. Self-defence is only a valid defence if; 1) you were under a reasonable fear of death or serious bodily harm, and 2) you believed that there was no other way to protect yourself, or your personal property. It is also possible to use this defence if you acted in defence of others. However, no matter the circumstances, you cannot use more force than is necessary to prevent the assault or its repetition.