Even if the Crown proves that the accused committed the prohibited act and had the required fault element, the accused may still avoid conviction by raising a relevant defence. Some common defences, such as mistake of fact and intoxication, are not really defences, but conditions that prevent the Crown from proving the required mental or fault element beyond a reasonable doubt. A person accused of murder could be so intoxicated that he or she did not know that the victim was likely to die. Likewise, a hunter accused of murder could commit the prohibited act of causing another hunter’s death but have had the mis-
taken impression that he or she was shooting a deer. In such instances, the Crown can prove the commission of the prohibited act, but will be unable to prove that the accused had the mental element required for murder. The defences of intoxication and mistake of fact are derived from the fault element of the particular crime. For example, an offence requiring objective negligence will allow a defence of mistake of fact only if the mistake was a reasonable one. It will also generally not allow any intoxication defence because the reasonable person is sober.
Other defences may excuse or justify conduct, even though the accused committed the offence with the required fault element. Those who defend themselves may have a defence of self-defence, even if they intentionally kill or harm the attacker. Self-defence is usually considered a defence that justifies conduct, and it leads to a full acquittal. Those who commit a crime in reasonable response to serious threats of harm by third parties may have a defence of duress, even if they commit the crime with the required fault element. An example would be the person who goes along with a robbery with a gun at his or her head. Similarly, a person who commits a crime in response to circumstances of dire peril may have a defence of necessity. This would apply to a lost hiker who intentionally breaks into a cabin because he or she desperately needs food and water. Those who have valid defences of duress and necessity act in a morally involuntary manner because in the dire circumstances it was impossible for them to comply with the law and there was no safe and lawful avenue of escape. The defences of necessity and duress are usually thought to excuse conduct, but they also lead to a full acquittal.
Defences are related to the appropriate disposition of the accused. The...