The principle that ignorance of the law is not a defence is a cornerstone of Canadian criminal law. Under the Criminal Code , section 19 states that a person cannot avoid liability simply because they did not know their actions were illegal.
However, the legal reality is more nuanced. While a mistake of law rarely excuses criminal conduct, Canadian courts recognize that a mistake of fact may affect whether the required intent exists. This distinction plays a critical role in determining criminal liability, particularly where the accused acted on an honest but mistaken belief about the situation.
Understanding how mistakes of fact and mistakes of law operate is essential because these concepts are closely tied to how courts assess intent, responsibility, and fairness in criminal proceedings.
Although these two concepts are often mentioned together, they play very different roles in Canadian criminal law . Understanding the distinction is essential because it directly affects whether a defence may be available and how courts assess criminal responsibility.
In Canadian criminal law, most offences require proof of two essential elements:
The Crown must prove both elements beyond a reasonable doubt to secure a conviction.
A mistake of fact can directly affect whether mens rea exists. If an accused honestly believed in a set of facts that, if true, would make their actions lawful, they may lack the required intent.
By contrast, a mistake of law does not usually impact liability. Even if a person genuinely misunderstands the law, that misunderstanding will not excuse the offence.
| Issue | Mistake of fact | Mistake of law |
|---|---|---|
| What the person got wrong | A factual circumstance (e.g., ownership, identity, what was said or done) | The legal rule itself (e.g., “I didn’t know that was illegal”) |
| Usual legal effect | May negate mens rea and raise a reasonable doubt | Generally no defence — s. 19 |
| Typical result if accepted | Acquittal (or failure of the Crown’s case on intent) | Conviction still available if the act and fault are otherwise proved |
| Narrow carve-outs | Offence-specific limits (e.g., sexual-assault belief in consent under s. 273.2) | Rare doctrines such as officially induced error — not a general excuse |
Mistake of fact is one of the most important concepts in criminal defence because it directly relates to intent. In many cases, the success of this argument depends on whether the accused can demonstrate a genuine misunderstanding of the situation rather than a deliberate act.
A mistake of fact argument applies when the accused had an honest belief in circumstances that, if true, would make the act lawful. For most true-crime offences, that belief does not need to be correct — but it must be genuine, and it must relate to a fact that matters to the mental element of the charge.
Canadian courts focus on whether:
If these conditions are met, the accused may lack mens rea, potentially resulting in an acquittal. Once there is an air of reality to the claim, the Crown must still prove the mental element beyond a reasonable doubt.
Courts do not automatically accept a claimed mistake. Instead, they evaluate the surrounding evidence to determine whether the belief is credible.
Key factors include:
“In practice, courts in Canada do not simply accept that an accused claims a mistake of fact. The court will closely examine whether the belief was genuinely held and whether it relates directly to the mental element of the offence. If the belief is inconsistent with the evidence or appears to be a justification created after the fact, it will not succeed. However, where there is a credible and honest misunderstanding of the situation, this can completely undermine the Crown’s ability to prove intent beyond a reasonable doubt.” — Brian Brody, Criminal Defence Lawyer
Unlike a mistake of fact, a mistake of law is governed by a strict legal rule in Canada. This principle reflects the expectation that individuals are responsible for understanding the legal consequences of their actions.
Section 19 of the Criminal Code establishes that ignorance of the law is not an excuse. This reflects a fundamental principle: individuals are expected to know the law governing their conduct.
As a result, misunderstanding legal rules does not eliminate criminal responsibility, even if the mistake was made in good faith — including reliance on a private lawyer’s incorrect advice in ordinary circumstances.
Although the rule is strict, courts recognize that certain rare situations may raise issues related to mistake of law.
These may include:
These situations do not create a general defence. Officially induced error, where it applies, is a limited excuse rooted in fairness — not a free-standing right to misunderstand the Criminal Code .
In practice, mistake of fact is simply the mens rea point above applied to real files: the Crown still has to prove intent, and an honest belief about a key fact can raise a reasonable doubt. Mistake of law almost never does that work under s. 19.
A mistake of fact is not usually pleaded as a standalone “affirmative defence.” It challenges the Crown’s ability to prove mens rea beyond a reasonable doubt — subject to any offence-specific reasonableness or “reasonable steps” rules Parliament has added.
A common example arises in theft-related situations. Someone takes a bag from a public setting, honestly believing it is their own. Evidence that they owned a similar item, had it earlier, and behaved consistently with that belief may support the argument that there was no intent to steal. The issue is not whether the act occurred, but whether the accused intended a criminal offence.
Mistake of fact is particularly complex where the claim is belief in consent. Under s. 273.2 , belief in consent is not a defence where it arose from self-induced intoxication, recklessness or wilful blindness, or circumstances where the Code says no consent is obtained — or where the accused did not take reasonable steps, in the circumstances known to them at the time, to ascertain that the complainant was consenting. Courts look for affirmative communication, not assumptions. Supreme Court guidance in Pappajohn and Sansregret , read with modern s. 273.2, still requires evidence of communicated consent rather than speculation.
Mistake of fact does not apply in the same way where subjective intent is not required — including many strict liability regulatory offences (where due diligence may be the real issue). Impaired-driving files also turn on specific Part VIII.1 elements (impaired operation, over 80, refusal) rather than a free-floating “I didn’t know the limit” narrative.
In practice, a mistake of fact is often used as part of a broader defence strategy rather than as a standalone slogan. Defence lawyers assess whether the evidence supports a genuine misunderstanding of the situation and whether that misunderstanding raises a reasonable doubt about intent.
A successful argument based on a mistake of fact typically involves:
Defence counsel will carefully analyze all available evidence, including witness testimony and surrounding circumstances, to reinforce the argument that there was no criminal intent.
A mistake of fact involves an incorrect belief about a situation that may negate intent (mens rea), while a mistake of law refers to misunderstanding the law itself and is generally not a valid defence under section 19 of the Criminal Code .
Yes, if the accused honestly believed in a set of facts that would make their actions lawful, the court may find that mens rea is missing, which can result in an acquittal — subject to any special statutory limits for that offence.
Canadian law follows the principle that everyone is expected to know the law. Section 19 of the Criminal Code clearly states that ignorance of the law does not excuse criminal liability.
It can be used when the accused had an honest belief about a key fact related to the offence, and that belief, if true, would make the act lawful — and where any offence-specific limits (such as s. 273.2 in sexual assault) are met.
No, it generally applies to offences requiring proof of a subjective mental element. It does not apply in the same way to many strict-liability or regulatory offences.
Courts assess whether the belief was genuinely held by examining evidence, consistency of the accused’s explanation, and whether the belief aligns with the surrounding circumstances.
Yes, but only in limited situations. The accused must show an honest belief in communicated consent that survives s. 273.2 — including reasonable steps — not assumptions or reckless indifference.
In rare cases, such as officially induced error based on incorrect advice from an authorized official, courts may consider a limited excuse. That is not the same as a general “I didn’t know the law” defence under section 19.
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Legally Reviewed by
Jeff Mass
| Updated: August 26, 2026
