Ontario Negligence Law: Duty, Standard of Care, and Causation

Elements of a Negligence Claim

To succeed in negligence, a plaintiff must establish on a balance of probabilities:

1. The defendant owed the plaintiff a duty of care
2. The defendant breached the standard of care
3. The breach caused the plaintiff's loss (causation)
4. The loss was not too remote (remoteness)
5. Actual damages

Duty of Care: The Anns/Cooper Test

The foundational duty of care test in Canada is the two-stage Anns/Coopertest, reformulated by the Supreme Court of Canada in Cooper v Hobart, [2001] 3 SCR 537, and clarified in Edwards v Law Society of Upper Canada, [2001] 3 SCR 562 and Design Services Ltd v Canada, [2008] 1 SCR 737:

Stage One — Prima facie duty:

• Proximity: Was there sufficient proximity between the parties that it is fair to impose a duty? Proximity is assessed from the perspective of the type of relationship, the nature of the act and loss, and any direct/indirect dealings between the parties. Recognized categories of proximity include manufacturer-consumer, employer-employee, professional-client, and occupier-entrant.
• Reasonable foreseeability: Was it reasonably foreseeable that the defendant's conduct could cause damage to a person in the plaintiff's position?

If both proximity and foreseeability are satisfied, a prima facie duty of care arises.

Stage Two — Policy considerations: Are there residual policy considerations that negate or limit the prima facie duty? Policy considerations include: indeterminate liability (floodgates concern — Hercules Management v Ernst & Young, [1997] 2 SCR 165); conflicting statutory duties of the defendant; and concerns about overlapping judicial and regulatory functions.

Novel duties: Where a plaintiff relies on a recognized category of proximity, the court proceeds directly on established precedent. Where no recognized category exists, the full two-stage analysis is required.

Standard of Care

The standard of care in negligence is the objective standard of the reasonable person in the circumstances of the defendant:

• Ordinary persons: The reasonable person of ordinary prudence. The defendant's subjective characteristics (intelligence, experience) are generally irrelevant.
• Professionals: The standard is the reasonably competent practitioner in the relevant field and specialty. Experts must meet the standard of the specialty they hold themselves out as practicing (ter Neuzen v Korn, [1995] 3 SCR 674). The standard evolves with the state of medical/professional knowledge at the time of the alleged negligence.
• Children: Children are held to the standard of a child of the same age, intelligence, and experience in the circumstances (modified objective standard). An exception applies where the child is engaged in an adult activity (e.g., operating a motorboat).
• Utilities: The Bolam test (a UK standard requiring merely that the defendant act in accordance with a body of responsible professional opinion) was rejected in Canada. The court independently assesses what the standard required — expert evidence is valuable but not conclusive.

Causation

Causation is frequently the most contested element in negligence cases. Ontario applies a multi-step causation analysis:

But-For Test

The primary test is the but-for test: but for the defendant's negligence, would the plaintiff have suffered the loss? The plaintiff must prove on a balance of probabilities (more than 50%) that the negligence caused the loss (Clements v Clements, 2012 SCC 32).

Multiple sufficient causes: Where two defendants each negligently cause an injury that the other could also have caused alone (two fires combine to burn a house), the but-for test fails both defendants. Courts apply Cook v Lewis, [1951] SCR 830 — causation is made out against both, and the burden shifts to each defendant to disprove their causal role.

Material Contribution to Risk

The material contribution to risk (MCR) doctrine is a narrow exception to the but-for test (Clements at para 46): MCR applies only where:

• It is impossible to prove but-for causation due to factors outside the plaintiff's control (not merely evidentiary gaps)
• The plaintiff's injury falls within the ambit of the risk that made the defendant's conduct negligent
• The defendant's negligence materially contributed to the risk of injury

MCR is not a general relaxation of the causation standard — it applies in exceptional cases only. Courts in Ontario have resisted expanding MCR beyond the scenarios contemplated in Clements.

Loss of Chance

Ontario courts have generally not adopted a loss-of-chance doctrine in medical negligence cases. The plaintiff must prove that the negligence caused the injury, not merely that it reduced a statistical chance of a better outcome (though this remains an evolving area).

Remoteness

Even where causation is established, a defendant is not liable for losses that are too remote. The test for remoteness in Canada is reasonable foreseeability of the type of damage (not the precise manner in which it occurred):

• Wagon Mound test: A defendant is liable only for damage of a type that was a reasonably foreseeable consequence of their negligence (not for entirely unforeseeable consequences).
• Thin skull rule: A defendant must take the plaintiff as they find them — if the type of damage was foreseeable, the defendant is liable for the full extent even if the severity was not foreseeable due to a pre-existing vulnerability (Athey v Leonati, [1996] 3 SCR 458).
• Crumbling skull: A defendant is not liable for pre-existing conditions that would have caused the same damage regardless of the negligence.Athey establishes that courts must apportion liability between the defendant's negligence and the pre-existing condition where the condition was going to worsen the plaintiff's situation anyway.

Contributory Negligence

Ontario's Negligence Act, RSO 1990, c N.1, replaced the common law all-or-nothing contributory negligence rule with a system of proportionate fault:

• Apportionment: Where a loss is caused by the negligence of multiple defendants and/or the plaintiff's own negligence, damages are apportioned in proportion to each party's degree of fault (s.3).
• Plaintiff's contributory negligence: The plaintiff's damages are reduced proportionately by their own fault (s.4). Wearing a seatbelt, using a handrail, and not contributory negligence in failure to mitigate.
• Contribution between defendants: Under s.2, a defendant who pays more than their share of a judgment can claim contribution from co-defendants in proportion to their respective fault.
• Joint and several liability: The Negligence Act maintains joint and several liability — a plaintiff can recover the full judgment from any one defendant, even if that defendant was only 1% at fault, leaving that defendant to seek contribution from co-defendants.

Occupiers' Liability

The Occupiers' Liability Act, RSO 1990, c O.2, replaced the common law categories of invitee, licensee, and trespasser with a unified regime:

• Occupier: A person in physical possession of premises or who has responsibility for and control over the condition or activities on the premises or the persons allowed to enter (s.1). More than one occupier can exist for the same premises.
• General duty (s.3): An occupier owes a duty to take such care as is reasonable in all the circumstances to ensure that persons entering the premises are reasonably safe. The duty extends to hazards from the condition of the premises and activities carried on.
• Trespasser duty (s.4): The occupier's duty to trespassers is lower — not to create a danger with intent to harm or reckless disregard for the trespasser's presence. This applies unless the trespasser is on the property with criminal intent, in which case the occupier may use reasonable defensive force.
• Limitation of liability: Occupiers can restrict or exclude their duty to certain categories of entrant by agreement (subject to the duty to take reasonable steps to bring the restriction to the attention of the person).

Nervous Shock and Pure Psychiatric Injury

Ontario courts have recognized duties of care for pure psychiatric injury (not accompanied by physical injury) in limited circumstances:

• Immediate victim: A plaintiff who was themselves in the danger zone created by the defendant's negligence can recover for psychiatric injury on ordinary negligence principles.
• Secondary victim (bystander): A plaintiff who witnessed a traumatic event involving close relatives and suffered psychiatric injury may recover if they were a recognizable plaintiff (close tie of love and affection + proximity to the accident + direct perception) — Alcock v Chief Constable of South Yorkshire Police [1992] AC 310, applied in Ontario.

Summary

Ontario negligence law is structured around the Anns/Cooper duty test, the objective standard of care, and the but-for causation test (with the narrow MCR exception fromClements). The thin skull and crumbling skull rules from Atheyare essential for damages analysis. The Negligence Act's proportionate fault regime and joint and several liability combine to create a complex damages landscape in multi-party personal injury and professional liability cases.

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