Canadian Criminal Law/Defences
An accused person who is able to raise a defence can escape criminal liability for an offence that they could otherwise be convicted for.
Defences are often categorized as follows:
- Justification: a justifiable act is one that makes out the offence but is justified by the external circumstances in which the act was committed. (e.g. self-defence)
- Excuse: a criminal act is excused where the accused would have committed an undesirable criminal offence, for which punishment would be morally inappropriate due to the extenuating circumstances. (e.g. offences due to mental infirmities, duress)
- Affirmative Defence: a defence that, if proven, will eliminate liability despite all the elements of the offence having been made out
- Negating Defence: a defence that negates one more of the essential elements of the prosecution's case.
Under s. 794, the burden is on the defendant to prove an exception or excuse:
794 (1) No exception, exemption, proviso, excuse or qualification prescribed by law is required to be set out or negatived, as the case may be, in an information.
(2) The burden of proving that an exception, exemption, proviso, excuse or qualification prescribed by law operates in favour of the defendant is on the defendant, and the prosecutor is not required, except by way of rebuttal, to prove that the exception, exemption, proviso, excuse or qualification does not operate in favour of the defendant, whether or not it is set out in the information.
Excuses and justifications "do not negative the mens rea rather they operate by justifying or excusing what would otherwise be criminal conduct".
- R. v. Hibbert, 1995 CanLII 110 (SCC),  2 S.C.R. 973 (SCC) para. 47
Raising a DefenceEdit
Before the trier-of-fact can consider a defence, thus requiring the crown to disprove at least one of the elements of the defence beyond a reasonable doubt, there must be an "air of reality" to the defence.
The purpose of the air of reality test is to prevent "outlandish defences" being put to the jury that would be "confusing and would invite unreasonable verdicts."
- R. v. Cinous 2002 SCC 29, (2002), 162 C.C.C. (3d) 129 (S.C.C.) at paras. 53-54 and 65
- R. v. Cinous, 2002 SCC 29,  2 SCR 3 at 84