An accused person can escape criminal liability for an offence that they could otherwise be convicted for by sufficiently proving the existence of one or more established defences.
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, the punishment for the offence would be morally inappropriate due to the extenuating circumstances. (eg. offences due to mental infirmities, duress). Defence such as necessity and duress are excuses since they are founded in their moral involuntariness.
- 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 or more of the essential elements of the prosecution's case.
An affirmative defence is generally considered a type of justification defence.
Ignorance of the Law
By s. 19, the ignorance of the law is no defence. However, there are limited exception where the underlying belief is due to officially induced error or mistake of fact.
Ignorance of the law
19 Ignorance of the law by a person who commits an offence is not an excuse for committing that offence.
R.S., c. C-34, s. 19.
Whether the judge correctly put a defence to a jury is a question of law and reviewable on a standard of correctness.
Excuses and justifications do not "negative the mens rea rather they operate by justifying or excusing what would otherwise be criminal conduct". It is a "concessions of human frailty" when face with an untenable choice. Such conduct is not always morally blameless, however.
Burden to Prove Excuse
Under s. 794, the Code states that the burden is on the defendant to prove an exception or excuse:
No need to negative exception, etc.
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.
Burden of proving exception, etc.
(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.
R.S., c. C-34, s. 730.
The shifted burden found in s. 794(2) has been interpreted as applying only to the "narrow circumstances, usually regulatory offences, where a status in law has been conferred upon the accused who would otherwise be culpable". This section has no application to offences in s. 335(1.1) It has been applied in charges of refusal to give a breath sample under s. 254(5). As well as s. 145(3) breaches of conditions.
The section has been found to apply in regulatory provincial offences.
R v Hibbert, 1995 CanLII 110 (SCC),  2 SCR 973 (SCC) para 47
R v Ryan, 2013 SCC 3 (CanLII), per LeBel and Cromwell JJ, at para 23 - An excuse does not negate the wrongfulness of the act.
- Ryan, ibid. at para 23 citing R v Ruzic, 2001 SCC 24 (CanLII)
- Ryan, ibid. at para 23
e.g. Refusal (Offence)
R v Greenshields, 2014 ONCJ 35 (CanLII) at para 16
R v Taraschuk, 1975 CanLII 37 (SCC),  1 SCR 385
see also Intention
R v PH, 2000 CanLII 5063 (ON CA) at para 14
- PH, ibid. at para 14
R v Goleski, 2015 SCC 6 (CanLII)
R. v. A.M.Y., 2017 NSSC 99
c.f. R v Truong, 2008 BCSC 1151 (CanLII), per Smart SCJ, at para 24
e.g. R v DMH, (1991) 109 NSR (2d) 322 (CA), per Hart JA
R v TG, (1998), 165 NSR (2d) 265 (CA), per Chipman JA at paras 15 to 19
Raising a Defence
Types of Defences
- Reasonable Excuse
- Self-Defence and Defence of Another
- Defence of Property
- Acting in Authority
- Officially Induced Error
- Corrective Force
- Accident and Mistake
- De Minimus Non Curat Lex
- Due Diligence
- Alternative Suspect Defence
- Innocent Possession
- Mistaken Belief of Age