Necessity, Duress & Impossibility
- Lesson 16 of 24
- Advanced
- Excuses: Moral Involuntariness. Statutory s. 17 and common law duress (Ryan) vs emergency necessity (Perka).
- 12 min
- Reviewed
By James R. GosnellEducational material, not legal advice.
Key points
Necessity and duress excuse conduct only when their distinct conditions for constrained choices are met, while impossibility requires objective inability to comply despite the required efforts. Once a defence has an air of reality, the prosecution must disprove an essential condition beyond a reasonable doubt to exclude it.
The lesson's scenario
The Impaired Driver Fleeing Active Gunfire Toward Immediate Shelter
Go to the worked example- Builds on
- Lesson 15 analyzed when the law justifies physical force used to protect people or property.
- This lesson
- Moral involuntariness: necessity's three conditions (imminent peril, no reasonable legal alternative, objective proportionality), duress by coercive threat, and objective impossibility.
- Leads to
- Lesson 17 examines the partial defence of provocation, which can reduce murder to manslaughter.
A three-pass reading method
- Start with the worked example. Seeing the facts first anchors the abstract rules.
- Read the doctrine: the statutory elements, the fault standard and the leading cases. Note the tests judges apply.
- Finish with the practice checklist and the recall cards at the end of the lesson.
Overview
and excuse otherwise criminal conduct where the legally required conditions of moral involuntariness are met. addresses an objectively insurmountable inability to comply with the law. These are distinct defences with demanding conditions. A personal belief that breaking the law was preferable, a threat causing ordinary anxiety, or serious inconvenience does not by itself justify an acquittal.
Learning Objectives
- Distinguish necessity, coercive threats and objective impossibility.
- Apply the correct objective, modified objective and subjective inquiries.
- Identify offence exclusions and distinguish evidentiary from persuasive burdens.
Necessity
The three cumulative conditions
Necessity is a common-law excuse preserved by section 8(3) of the Criminal Code. Perka and Latimer identify three conditions: , no reasonable legal alternative, and between the harm inflicted and the harm avoided. Moral involuntariness explains the defence; it does not replace these conditions with an unrestricted assessment of compassion or fairness.
The danger must be pressing, not a speculative or distant possibility. The accused's perception of peril and of the absence of a legal alternative is assessed on a : reasonable beliefs in the circumstances, with relevant personal characteristics considered. Purely personal conviction that the conduct was necessary is insufficient. Investigate available assistance, lawful routes, opportunities to wait safely and whether the prohibited conduct continued after the danger passed.
Proportionality is assessed objectively, without adopting the accused's personal valuation of the interests involved. The harm inflicted must not exceed the harm avoided. Necessity differs here from duress, whose proportionality inquiry uses a modified objective standard.
Prior conduct and homicide
Prior negligence or unlawful activity does not automatically exclude necessity. It matters whether the emergency was foreseeable and whether the accused's prior choices undermine the claim that lawful compliance was realistically unavailable. Perka does not establish that every emergency arising during illegal activity is unanswerable by necessity. Equally, a person cannot convert a foreseeable difficulty with available lawful solutions into an unavoidable emergency simply by proceeding.
In Latimer, the defence lacked an air of reality on its conditions. The decision does not establish a categorical rule that necessity can never arise on a murder charge. The objective proportionality requirement is particularly demanding where the accused intentionally kills another person; it cannot be satisfied merely by asserting a benevolent motive.
Applying the test to an emergency
Factual Scenario
In this hypothetical, an impaired person is sitting in the driver's seat of a parked car when an unexpected confrontation nearby turns into gunfire directed toward the car. Their sober passenger does not know the roads. The driver immediately travels a short distance on an empty road to an occupied building offering shelter, then stops and requests help. The Crown argues that the passenger could have driven or that they could have called police without moving. Assume the impaired-driving offence is otherwise proved.
Gunfire toward the car supports imminent peril. The alternatives must be assessed realistically in the seconds available: switching seats, explaining the route or waiting for police may not provide a reasonable legal escape. The passenger's sobriety is relevant, but is not conclusive where unfamiliarity with the roads and the urgency make taking over impractical. JurisClasseur's examples specifically reject treating an alternative driver as automatically decisive (nos 14–16).
Objective proportionality still requires comparing the harm of the impaired driving with the danger avoided. The short route, empty road and prompt stop support the defence; impairment and any risk imposed on others count against it. Fear does not itself settle that comparison. These facts can give all three conditions an air of reality. The Crown must then disprove one beyond a reasonable doubt; absent such disproof, the applicable necessity defence requires acquittal.
Variation
After reaching shelter and learning the attacker has left, the driver instead continues home through busy streets, although the passenger can now drive safely. The driver says they remain frightened.
Reassess the later driving. Available shelter and a capable driver undermine both continuing imminent peril and the absence of a legal alternative; the added risk to road users also changes proportionality. The Crown can defeat the defence by disproving one condition for the conduct charged. An initial emergency does not excuse the entire journey. Conversely, prior drinking alone did not automatically exclude the first claim: the relevant inquiry included whether that unexpected emergency was foreseeable.
Duress
Threats compelling the offence
Duress concerns express or implied threats of death or bodily harm to the accused or another person, made to compel the accused to commit the offence. Bodily harm is sufficient; the threat need not be lethal. General fear of someone, a desire for money or a threat unrelated to compelling the charged conduct does not automatically establish duress.
Section 17 applies to principal offenders. A common-law defence applies to secondary parties, including the forms of participation discussed in Paquette and Hibbert. In Ruzic, the Supreme Court invalidated the statutory requirements of the threatener's presence and immediate execution of the threat. It did not strike down the entire section or dispense with the need for a sufficiently close temporal connection.
Factual Scenario
Consider a separate hypothetical: an armed person threatens to shoot a driver unless the driver transports stolen goods to a warehouse. Compare two changed facts: the gunman makes no demand and the driver instead damages a stranger's gate to escape; or the driver strikes the gunman to stop the threatened shooting.
The demanded transport points to duress: a qualifying threat compels the particular offence. The Crown may dispute safe alternatives or the temporal connection, and the accused's participation route and any offence exclusion must first be checked. Damaging the stranger's gate as a chosen escape points to necessity; there was no demand to commit that offence, and all three necessity conditions remain necessary. Striking the gunman points to self-defence under section 34. Ryan prevents using duress merely to fill a failure of self-defence when force is directed against the threatener.
None of these facts describes objective impossibility: each involves choosing an unlawful response to danger. For each applicable defence, evidence must support every condition before the Crown must disprove one beyond a reasonable doubt. Selecting the route does not establish its success (no 27; no 45).
Variation
A different driver, travelling slowly with sound tires on an apparently clear road, encounters an invisible patch of ice. Despite braking and attempting to steer within the lane, the vehicle slides across a prohibited line. The driver points to photographs, vehicle records and observations supporting the absence of warning and the inability to retain traction.
This raises impossibility: the alleged breach results from inability to keep the vehicle within the line, rather than a decision to cross it as the lesser harm. The evidence addresses an unforeseeable external condition, precautions and efforts to comply. The Crown may dispute that the ice was unforeseeable, the speed was appropriate or the loss of control unavoidable. The ultimate question is whether a reasonable driver in analogous circumstances would likewise have been unable to comply, not merely whether this driver acted understandably. If every condition has an air of reality, the Crown must exclude one beyond a reasonable doubt. The source's ice examples turn on concealed ice and impeccable driving, not on ice alone (nos 48–52).
Belief, escape and temporal connection
The accused must reasonably believe that the threats will be carried out, have no and face a close temporal connection between the threats and the threatened harm. These inquiries require a practical assessment of the person's circumstances and relevant characteristics. The possibility of safe escape remains relevant until the offence is complete.
There is no standalone rule requiring a call to the police in every case. A safe, realistic opportunity to obtain protection can defeat the defence, but evaluate whether such assistance was actually available in context. Trauma, isolation, the threatener's reach and the location can matter; they do not create automatic exemptions from the legal test. A remote threat followed by prolonged voluntary participation may undermine the required connection and the absence of alternatives.
A timeline must identify the particular offence's completion point. JurisClasseur's importation example does so: the court treated the drug-importation offence as incomplete until passage through Canadian customs and found a safe opportunity to seek help from the Canadian authorities present on arrival. Duress therefore failed despite the earlier threats. The source also describes an accessory-after-the-fact case where an opportunity to call police arose before the assistance was complete (no 31).
The lesson is to test the initial compulsion, each later opportunity for protection and the legally relevant completion point. The Crown can rely on a later safe opportunity; evidence of the coercer's continuing reach or control over a threatened third person may support the defence in a different case. Neither police presence nor continuing subjective fear settles the issue abstractly. Once the complete defence has an air of reality, the ultimate burden remains the Crown's (nos 29–31).
Proportionality and criminal association
Duress proportionality has two aspects: the threatened harm must be at least as serious as the harm inflicted, and the accused's conduct must satisfy society's expectations of reasonable resistance in similar circumstances. The modified objective standard recognizes ordinary human limits without accepting every personally understandable reaction. Equality between the threatened and inflicted harms does not alone establish the defence.
Voluntary involvement in a conspiracy or criminal association with subjective awareness of a risk of coercion can exclude duress. Do not substitute a bare finding of association or objective foreseeability for the required inquiry into the accused's knowledge. The circumstances of entry, continued participation and any actual withdrawal matter.
Excluded offences and authority
Section 17 excludes numerous offences, including murder, attempted murder, specified sexual and other assaults, robbery and arson. The statutory and common-law routes must be distinguished. JurisClasseur discusses Aravena, where the Ontario Court of Appeal accepted the availability of common-law duress to a secondary party charged with murder, and Willis, where the Manitoba Court of Appeal upheld the statutory murder exclusion for principals.
The Supreme Court left the broader exclusions questions unresolved in Ruzic and Ryan. Trial decisions invalidating particular exclusions do not establish that the entire list is inoperative throughout Canada. Identify the charged offence, the participation route, the court's jurisdiction and the authority of the relevant decision before asserting availability or exclusion.
Impossibility
Objective inability to comply
Impossibility concerns total inability to comply, assessed objectively through a reasonable person in analogous circumstances. JurisClasseur explains it through an external, unforeseeable situation and an irresistible obstacle: the defendant must not have caused the impediment through their own fault, must have made the required efforts to overcome it, and a reasonable person would likewise have failed. Personal inconvenience or economic difficulty is insufficient.
In Strasser, an alternative route and the later removal of an obstruction defeated the alleged impossibility of reaching work. Similarly, a hidden road sign or unexpected ice calls for analysis of visibility, reasonable precautions, foreseeability and the ability to comply; it does not automatically establish the defence. A labour shortage requires evidence of the steps taken and the objective inability to comply, not a bare assertion that lawful staffing was difficult.
Distinction from due diligence
Impossibility is available through section 8(3), and in Quebec provincial penal proceedings through article 60 of the Code of Penal Procedure, subject to the governing law. JurisClasseur recognizes its possible application even to absolute-liability offences. Absolute liability excludes , not every defence.
For strict liability, due diligence asks whether the defendant took all reasonable precautions and is ordinarily proved by the defendant on a balance of probabilities. Impossibility asks whether compliance was objectively impossible despite the required efforts. Its ultimate burden is different: once supported by an air of reality, the prosecution must exclude it beyond a reasonable doubt. That lower evidentiary burden does not make its substantive conditions easier to meet.
Proof and Outcome
Air of reality and ultimate burden
Each defence requires evidence capable of supporting every essential condition. At the air-of-reality stage, the judge considers the whole record and the inferences reasonably available without deciding credibility as the trier of fact would. Evidence may come from either party; the accused need not necessarily testify.
Once properly in issue, necessity, duress and impossibility must be excluded by the prosecution beyond a reasonable doubt. Disproving one essential condition suffices. If the prosecution cannot exclude an applicable defence, the result is an acquittal. Relevant pressure or hardship may still inform sentencing when a complete defence fails, but mitigation is a separate analysis.
Practice Checklist
- Identify the source of the danger, the charged conduct and the correct defence.
- Build a timeline including safe alternatives before the offence was complete.
- Apply the correct standard to each condition, particularly proportionality and prior conduct.
- For duress, verify principal or secondary participation and the applicable exclusions.
- Distinguish objective impossibility from due diligence and apply the correct burdens.
Check your understanding
Two short exercises before you move on: reason through the lesson’s worked examples, then recall its key terms from memory.
Apply the rules
Each worked example gives the facts first and keeps its analysis closed. Decide the outcome, then open the analysis to compare.
Active recall
1 / 8Formulate your answer before revealing the definition. Your self-assessment schedules a review; it does not measure mastery.
Necessity
Nécessité
How would you define this concept? Which conditions or limits matter?
Glossary
- Due diligenceDiligence raisonnable
- Taking all reasonable precautions, ordinarily established by the defendant on a balance of probabilities in strict liability.
- DuressContrainte
- An excuse for conduct compelled by qualifying threats, subject to escape, temporal, proportionality and other requirements.
- Imminent perilPéril imminent
- A pressing danger, rather than a speculative or distant possibility, required for necessity.
- ImpossibilityImpossibilité
- Objective inability to comply despite the required efforts and without culpably causing the obstacle.
- Modified objective standardNorme objective modifiée
- Assessment from the perspective of a reasonable person with the accused’s relevant characteristics in similar circumstances.
- NecessityNécessité
- An excuse requiring imminent peril, no reasonable legal alternative and objective proportionality.
- ProportionalityProportionnalité
- Comparison of inflicted and avoided or threatened harm, assessed objectively for necessity and on a modified objective standard for duress.
- Safe avenue of escapeIssue sûre
- A realistic way to avoid the threatened harm, whose availability must be assessed in context until the offence is complete.
References and Further Reading
- JurisClasseur Québec, Droit pénal général, ; merged PDF pp. 638–673, especially nos 9–19, 20–26, 29–44 and 45–53.
- Criminal Code, ss. 8(3), 17 and 21; Quebec Code of Penal Procedure, art. 60; Canadian Charter of Rights and Freedoms, s. 7.
- Perka v. The Queen, [1984] 2 S.C.R. 232; R. v. Latimer, 2001 SCC 1; R. v. Ruzic, 2001 SCC 24; R. v. Ryan, 2013 SCC 3; R. v. Aravena, 2015 ONCA 250; R. v. Willis, 2016 MBCA 113; Strasser v. Roberge, [1979] 2 S.C.R. 953, as analyzed in the fascicule.