Our hub page includes a short overview of common criminal defences, touching on issues like Charter breaches, identification, alibi, consent, and insufficient evidence. This article is the full-length companion to that overview: it goes deeper into each category, explains how these ideas tend to actually come up in Ontario cases, and is meant to be read as general background, not as a checklist for evaluating any specific charge.
The most important point to keep in mind throughout this guide is one that bears repeating: whether any defence applies to a real case depends entirely on the specific evidence involved, and only a lawyer who has reviewed the actual disclosure in that case can meaningfully assess it. Nothing here is a substitute for that review.
Self-Defence
Self-defence generally involves the idea that a person used force to protect themselves, or in some cases another person, from an actual or perceived threat. In Ontario cases, this is not simply a matter of showing who started a physical confrontation. Courts generally look at a range of factors, including the nature of the perceived threat, whether the person's response was reasonable in the circumstances, and what alternatives, if any, were realistically available. See our assault charge page for how self-defence considerations can intersect with a specific charge.
Because this analysis is so fact-dependent, two cases that sound superficially similar can be assessed very differently depending on details such as the relative size or history between the people involved, whether a weapon was present, and how the confrontation actually unfolded.
Identity and Mistaken Identity
In some cases, the central issue is not what happened, but who did it. Identification evidence, particularly eyewitness identification made under stressful or brief circumstances, has long been recognized as an area where errors can occur. Where identity is genuinely in dispute, a case can turn heavily on the quality and reliability of identification evidence, including how and when a witness was asked to identify a suspect, and whether other evidence, such as surveillance footage or digital records, supports or contradicts that identification.
Alibi
An alibi defence involves evidence that the accused was somewhere else, or doing something else, at the time the offence is alleged to have occurred, making it impossible for them to have committed it. Alibi evidence can come from other people, from records such as time-stamped receipts or digital location data, or from a combination of sources. Because an alibi is only as strong as the evidence supporting it, and because it can be undermined if it is not raised and investigated promptly, this is an area where speaking with a lawyer as early as possible tends to matter a great deal.
Charter Breaches and Exclusion of Evidence
As discussed in more depth in our Charter rights guide, a breach of a person's Charter rights, such as an unlawful search or a failure to provide timely access to a lawyer, does not amount to a defence to the underlying charge in the traditional sense. Rather, it can potentially lead to a remedy, most commonly the exclusion of evidence obtained through the breach under section 24(2) of the Charter. Where key evidence is excluded, the Crown's ability to prove the case can be significantly weakened, though this outcome depends on a separate legal analysis and is never automatic.
Charter-based arguments generally require a detailed review of exactly what police did, in what order, and under what legal authority. This is one of the areas where reviewing full disclosure, rather than relying on a summary, makes the biggest practical difference.
Mistake of Fact
A mistake of fact defence generally involves the idea that the accused held an honest, though mistaken, belief about a factual circumstance that, if true, would have made their conduct lawful. This is a narrow and fact-specific concept, and how it applies can vary considerably depending on the offence involved and the nature of the mistake claimed. It is not a general excuse for having been wrong about something; the mistake generally needs to relate directly to an element of the offence itself.
Necessity and Duress
Necessity and duress are related but distinct concepts that, in general terms, involve a person acting unlawfully because of extraordinary pressure. Necessity typically relates to being compelled to act by circumstances, such as an emergency situation with no reasonable legal alternative, while duress typically relates to being compelled to act because of a threat made by another person. Both are treated as narrow defences with strict requirements, and both require a genuinely exceptional set of circumstances rather than ordinary difficulty or pressure. See our theft charge page for an example of a charge where these kinds of arguments occasionally arise.
Mental Disorder: A Distinct, Specialized Area
A finding that a person is not criminally responsible on account of mental disorder, often referred to by the abbreviation NCRMD, is a separate and highly specialized area of criminal law, distinct from the defences discussed above. It does not result in either a conviction or a straightforward acquittal, and it leads to its own distinct process, generally involving assessment and oversight by a review board rather than a traditional sentence. Because of its complexity, this is an area that typically calls for lawyers with specific experience in mental-disorder matters, and it is mentioned here only to flag that it exists as a distinct path, not to describe how it works in detail.
It is a mistake to assume that any one of these categories automatically applies just because it sounds like it fits the general shape of what happened. Each of these concepts has specific legal requirements, and applying them to a real case requires a careful, evidence-based assessment by a lawyer, not a general comparison to a description like this one.
How a Defence Strategy Is Actually Decided
In practice, a defence strategy is not chosen off a list. It develops out of a careful review of the disclosure provided by the Crown, discussions with the client about their own recollection of events, and, where relevant, independent investigation or expert input. Multiple categories of argument, such as a Charter issue and a factual dispute about identity, can sometimes apply to the same case, and a lawyer will generally consider how they fit together rather than treating them as separate, isolated options.
This process typically continues right up to, and sometimes through, a trial, since new information from ongoing disclosure or witness preparation can shift how a case is best approached. This is part of why it is generally unwise to settle on a fixed theory of a case very early on, before the full picture is available.
Frequently Asked Questions
How do I know which defence applies to my case?
This is not something that can be determined from a general article. Whether any defence applies, and how strongly, depends entirely on the specific evidence in your case, and only a lawyer who has reviewed the disclosure can meaningfully assess this.
Is self-defence the same as saying the other person started it?
Not exactly. Self-defence generally involves a broader legal assessment of the perceived threat and the reasonableness of the response, not simply who acted first. Whether it applies depends on the specific facts.
Can a Charter breach be raised as a defence on its own?
A Charter breach is not a defence to the underlying allegation in the traditional sense, but it can lead to a remedy, such as the exclusion of evidence, which can significantly affect the Crown's ability to prove the case. This depends on a separate legal analysis.
What is the difference between necessity and duress?
In general terms, necessity relates to being forced to act by circumstances, such as an emergency, while duress relates to being forced to act by a threat from another person. Both are narrow, fact-specific defences with strict requirements.
Is NCRMD the same as a not guilty verdict?
No. A finding of not criminally responsible on account of mental disorder is a distinct, specialized outcome that leads to a different process than either an acquittal or a conviction. It requires its own specific evidence and is generally handled with the involvement of specialized counsel.
Do I need to decide on a defence before I see disclosure?
No, and it is generally unwise to commit to a theory of the case before disclosure has been received and reviewed. See our disclosure guide for more on why this stage matters so much.
Related Insights
This article is general legal information, not legal advice, and does not create a lawyer-client relationship. Criminal procedure can vary by case, courthouse, and circumstance. Confirm current requirements with a qualified lawyer or an official source before relying on anything here.