Why "I Didn't Know" Is Usually Not a Defence in Criminal Court

It is one of the most common things a person says when they are charged: “I didn’t know that was illegal.” Or “Nobody told me I couldn’t do that.” Or “My lawyer at the bail hearing never explained that condition to me.”

It feels unfair that a person could be convicted of a crime they did not realize they were committing. But the answer in Canadian criminal law is, almost always, the same: ignorance of the law is not a defence. The principle is so old it has a Latin name — ignorantia juris non excusat — and so important that Parliament wrote it directly into the Criminal Code.

This article explains where that rule comes from, why we have it, how it plays out in real cases (bail conditions, obscure offences, regulatory charges), and the narrow set of exceptions that actually exist.

The Statutory Rule: Section 19 of the Criminal Code

Section 19 of the Criminal Code says it plainly:

Ignorance of the law by a person who commits an offence is not an excuse for committing that offence.

That is the entire section. There is no carve-out for first-time offenders, no carve-out for laws that are obscure or counter-intuitive, no carve-out for people who genuinely had no idea their conduct was prohibited. If the Crown can prove the elements of the offence beyond a reasonable doubt, the fact that you did not know the conduct was illegal is, on its own, irrelevant.

Mistake of Law vs Mistake of Fact

The first thing to understand is the difference between a mistake of law and a mistake of fact, because the two are treated very differently.

• A mistake of law is what section 19 captures: you knew exactly what you were doing, but you did not know it was illegal. (“I didn’t know it was a crime to carry pepper spray in Canada.”) This is generally not a defence.
• A mistake of fact is different: you were mistaken about something in the world, and if the facts had been as you believed them to be, no offence would have occurred. (“I thought the jacket was mine — it was identical to the one I came in with.”) This can be a defence, depending on the offence.

Mistake of fact lives in a different legal universe than mistake of law. For most offences requiring intent, an honest mistake of fact that negates the mens rea (the mental element) of the offence is a defence. For some offences — sexual assault is the most important example — the mistake must also be reasonable in the sense that the accused took reasonable steps to ascertain the relevant facts (s. 273.2 of the Criminal Code).

The line between mistake of law and mistake of fact is not always obvious, and it is one of the most heavily-litigated areas of criminal law. But the basic rule holds: not knowing what the law says will not get you off. Not knowing what the world looked like sometimes will.

Why We Have This Rule

The rule looks harsh on first read. Why should it be a crime if the person genuinely did not know? There are several reasons, and they are all rooted in how a functioning justice system has to work.

Predictability and Equal Treatment

Imagine the alternative. If “I didn’t know” were a defence, every prosecution would turn into a credibility contest about what was inside the accused’s head at the moment of the offence. Two people doing exactly the same thing would face different outcomes based on nothing more than how convincingly each could claim ignorance. The well-informed would be convicted; the wilfully blind would walk free. That is not a workable system.

Incentives to Stay Informed

The rule creates a duty to find out. If you are about to do something where the legality is unclear, the law expects you to ask — to read the rule, to call a lawyer, to check the bail order. The cost of looking up the answer is small. The cost of allowing every accused to claim ignorance would be enormous.

The Crown Already Has to Prove Intent

For most criminal offences, the Crown must prove that you intended to do the prohibited act — not that you intended to break the law. If you punched someone, the Crown proves you intended to apply force. The Crown does not have to prove that you knew assault is in the Criminal Code. The mental element captures the relevant moral fault. Adding “knowledge of the law” on top would mean re-litigating Parliament’s choices in every single case.

Where This Comes Up in Real Cases

The abstract rule sounds fine. The problem is that it bites hardest in exactly the situations where the accused is most sympathetic. Three patterns come up over and over.

1. Bail Conditions People Did Not Understand

This is the most common scenario we see at our office. A person is released on bail with a long list of conditions — no contact with the complainant, residence requirements, curfews, no alcohol, no possession of cell phones, no attending certain addresses. The release order is read out quickly at a bail court already running behind. Duty counsel may have explained two of the eight conditions. The accused signs the document and goes home, exhausted.

A week later they are charged with breach of recognizance under s. 145 of the Criminal Code because they sent a “happy birthday” text to the complainant, or they had a beer at a family dinner, or they slept at their girlfriend’s place when their bail required them to reside at their parents’ address.

The defence “I didn’t realize that was a condition” is, in almost every case, a non-starter. The Crown is required to prove that you knowingly breached the order, but knowledge of the condition itself is much easier for the Crown to prove than knowledge of the legal consequence. Once the Crown puts the signed release order in front of the judge — and your signature on it — the burden of explaining your way out of it is heavy.

There are limited exceptions. If a condition was so vaguely worded that you could not have known what it required of you, that may be argued. If the condition was changed at a later appearance and the new version was never served on you, that is a real argument. But “I forgot” or “I didn’t read the whole thing” are not defences.

The lesson is straightforward: read every condition the day you are released, ask your lawyer to explain anything you do not understand, and if a condition is impossible or unworkable, apply to vary it before you breach it. We covered this in detail in our common bail variations guide and our breach of bail conditions explainer.

2. Offences You Did Not Know Existed

The Criminal Code is over 800 sections long, and there are dozens of other federal and provincial statutes that create criminal or quasi-criminal liability. Most people could not list ten specific Criminal Code offences off the top of their head. That does not help when they are charged with one.

A few examples we see regularly:

• Possession of property obtained by crime (s. 354). A person buys a used phone or bike from someone on Marketplace at a too-good-to-be-true price. The item turns out to be stolen. The Crown does not have to prove the accused knew for certain it was stolen — recklessness or wilful blindness can be enough.
• Uttering threats (s. 264.1). Many people do not realize that words alone — texted, posted, or shouted in anger — can found a criminal charge if a reasonable person would take them as a serious threat. The accused’s belief that “I was just venting” does not, on its own, defeat the charge.
• Possession of a prohibited weapon. Items that are legal in other countries — certain knives, brass knuckles, pepper spray, conducted energy weapons — are prohibited in Canada. Tourists and new immigrants are sometimes charged after going through airport security with items they bought legally elsewhere. “I didn’t know it was illegal here” is, again, not a defence under s. 19.
• Mischief (s. 430). Damaging property, including digital property, can be charged as mischief even when the accused believed they had a “right” to do it. The defence of “colour of right” is narrow and technical.

In all of these cases, the question is not whether the accused knew the law existed. The question is whether they did the prohibited act with the required mental state — usually some form of intention or recklessness about the facts, not about the legal classification.

3. Regulatory and Strict-Liability Offences

A separate category of offences — usually prosecuted under provincial or federal regulatory statutes (the Highway Traffic Act, the Liquor Licence Act, the Fisheries Act, securities legislation, environmental legislation) — operates on a different model entirely. Many of these are strict liability offences: the Crown only needs to prove the prohibited act, and the accused must then prove due diligence — that they took reasonable steps to comply with the law — to avoid conviction.

For these offences, “I didn’t know” is also typically not a defence, but for a different reason: the Crown was never required to prove you knew in the first place. The defence is “I tried my best to comply,” not “I had no idea this was a rule.” Showing that you researched the requirements, sought professional advice, or relied on official guidance can amount to due diligence. Showing that you simply never checked, generally cannot.

The Narrow Exceptions

There are a small number of doctrines that look like exceptions to s. 19. They are real, but narrow, and they almost never apply in the way non-lawyers expect them to.

Officially Induced Error

The Supreme Court of Canada recognized a narrow defence — first proposed by Chief Justice Lamer in R v Jorgensen and adopted unanimously by the Court in Lévis (City) v Tétreault — where the accused has been affirmatively misled by an official responsible for administering the law. To succeed, the accused must show: (1) that an error of law was made; (2) that the accused considered the legal consequences of the act; (3) that the advice came from an appropriate official; (4) that the advice was reasonable; (5) that the advice was erroneous; and (6) that the accused relied on the advice in committing the act.

This is much more demanding than “a police officer said it was probably fine.” Casual conversations, internet research, and bad advice from non-lawyers all fall outside the doctrine. Genuine, written, mistaken guidance from the regulator who administers the relevant statute can — sometimes — fall inside it.

Mistake About a Specific Legal Element of the Offence

A few offences are structured in a way that requires the Crown to prove the accused had knowledge of a specific legal fact — for example, that property was “stolen,” that a person was “lawfully” in a place, or that a previous court order was in force. A mistake about that specific legal element can defeat the mens rea. This is sometimes called the “mistake of law that is really a mistake of fact” issue. It is technical, offence-specific, and not something an accused can navigate without a lawyer.

Constitutional Vagueness

If a law is so vague that it gives no meaningful notice of what conduct is prohibited, it can be struck down under s. 7 of the Charter. This is not a defence about the accused’s personal ignorance — it is a constitutional challenge to the law itself. It is rare and difficult, but real. We discuss the broader landscape of Charter arguments in our Charter rights deep dive.

What This Means in Practice

Two practical lessons follow from all of this.

First, take legal documents seriously the day you receive them. A bail order, a probation order, a peace bond, or a restraining order is enforceable from the moment it is issued. You are presumed to know what is in it. If something is unclear, pick up the phone the same day. Our breach of bail conditions and practice area page on breach of conditions explain the consequences of getting this wrong.

Second, if you are charged with something you did not know existed, that is not the end of the case. It is the beginning of a different defence. The fight is rarely going to be “I didn’t know the law” — it is going to be about whether the Crown can prove the factual and mental elements of the specific offence beyond a reasonable doubt. That is the standard we explain in our article on reasonable doubt, and it is where most acquittals actually live.

A related question we hear from people whose charges have been withdrawn or who have been acquitted is whether they can sue the complainant or the police. The answer is more nuanced than most people expect, and we cover it in our companion article on whether you can sue after charges are dropped or you are found not guilty.

Contact a Criminal Defence Lawyer

If you have been charged with an offence you did not know existed, or breached a condition you did not understand, do not assume the case is hopeless — and do not assume that “I didn’t know” will fix it on its own. The defence has to be built around the actual elements of the actual offence, with a lawyer who knows where the real arguments are.

Call Mor Fisher LLP at 705-721-6642 for a free consultation, or contact us online. We defend clients in Barrie, Toronto, Orillia, Newmarket, Brampton, and throughout Central Ontario.