The “But For” Test: When Is an Express Counterfactual Analysis Required?
Trial judges are generally afforded considerable deference when making findings of fact, including whether a defendant’s negligence caused a plaintiff’s injuries. However, this deference is not absolute.
In Hemmings v. Padmore (“Hemmings“)[i], the Supreme Court of Canada (“SCC”) clarified the circumstances in which errors in a trial judge’s causation analysis may justify appellate intervention. The decision provides important guidance on the distinction between factual and legal errors, the required application of the established “but for” test, and the limits of appellate deference in negligence claims.
Background
The case arose from a medical negligence action brought by Sophia Hemmings and members of her family after Ms. Hemmings suffered a cardiac arrest during an emergency caesarean section, resulting in severe and permanent brain damage.
The plaintiffs alleged negligence by several healthcare practitioners involved in Ms. Hemmings’ pregnancy and delivery, including her treating obstetrician and the anesthesiologist who attended her delivery. The plaintiffs also sought to hold Scarborough Hospital (the “Hospital”) vicariously liable for the conduct of its Nurse.
At trial, the judge found the obstetrician, the anesthesiologist, and the Hospital all liable in negligence. On appeal, however, the Ontario Court of Appeal overturned the findings against the obstetrician and the Hospital while upholding the finding against the anesthesiologist.[ii]
Both the plaintiffs and anesthesiologist appealed to the SCC. The Court dismissed both appeals.
The differing outcomes turned, in part, on whether the trial judge’s findings on causation were entitled to appellate deference or were affected by errors of law requiring intervention.[iii]
Key Takeaway from Hemmings v. Padmore: The “But For” Test Does Not Always Require an Express Counterfactual
The established “but-for” test in negligence requires a plaintiff to demonstrate, on a balance of probabilities, that their injury would not have occurred but for the defendant’s negligence. This necessarily involves considering what would have happened had the defendant acted appropriately, a process known as a “counterfactual analysis.”[iv]
However, the SCC clarified that trial judges are not always required to expressly include the counterfactual analysis in their reasons. Where the connection between the defendant’s negligence and the resulting injury is clear and direct, requiring judges to explain what would have happened otherwise may be unnecessary. In such circumstances, courts may rely on common-sense inferences to establish causation.
The situation is different where the circumstances are more complex, particularly where multiple events or individuals may have contributed to the injury. In these cases, courts may need to undertake a more detailed counterfactual analysis to determine whether the defendant’s negligence actually caused the harm.
1. The Hospital and Nurse San Juan – Counterfactual Needed
In Hemmings, the trial judge found that the hospital’s nurse, Ms. San Juan, had negligently failed to review Ms. Hemmings’ medical records or advise her to seek medical attention during a telephone consultation. Ms. Hemmings had called the hospital complaining of frequent vomiting, but Ms. San Juan failed to review records that could have helped her assess whether the symptoms required urgent medical attention.[v] The trial judge concluded that this negligence contributed to Ms. Hemmings’ injuries, reasoning that she would likely have received earlier medical treatment had Ms. San Juan acted appropriately.
However, the SCC found that the trial judge had not adequately considered whether Ms. Hemmings would have suffered the same injuries even if Ms. San Juan had provided proper advice.[vi] Ms. San Juan’s negligence occurred approximately ten days before the emergency caesarean section. Unlike a situation where negligent conduct immediately causes an injury, several events and medical decisions stood between Ms. San Juan’s omission and Ms. Hemmings’ eventual injuries.
For example, it was necessary to consider whether Ms. Hemmings would have followed Ms. San Juan’s advice to seek medical attention, what treatment she would have received, and whether that treatment would have prevented her injuries.[vii] These questions could not simply be answered by assuming that earlier medical attention would necessarily have led to a different outcome.
A more thorough counterfactual analysis was therefore needed to determine whether Ms. San Juan’s negligence had actually caused the injuries. The SCC found that the trial judge had made an error of law by failing to adequately explain what would likely have happened had Ms. San Juan acted appropriately.
This error justified appellate intervention, and the Hospital was ultimately held not liable.
2. The Anesthesiologist – Counterfactual Not Needed
The trial judge also found that Dr. Jamensky, the anesthesiologist, had negligently converted Ms. Hemmings from regional to general anesthesia to address her panic without first taking reasonable steps to calm her. They concluded that this decision directly caused Ms. Hemmings’ cardiac arrest and resulting brain injury.[viii]
Dr. Jamensky argued on appeal that the trial judge had failed to adequately consider what would have happened had he exercised reasonable care before administering general anesthesia.[ix]
The SCC rejected this argument. Unlike Ms. San Juan’s negligence, which occurred over ten days before Ms. Hemmings’ injuries and involved several intervening events, Dr. Jamensky’s negligence occurred immediately before the cardiac arrest, creating a much clearer connection between his actions and the resulting harm.[x]
Importantly, the trial judge’s findings were also supported by largely uncontested expert evidence that patients experiencing panic during a C-section can almost always be calmed through appropriate measures. The trial judge had also accepted testimony from Ms. Hemmings’ sister that she was responsive and not moving around, suggesting that there was no immediate need to administer general anesthesia. Together, this evidence supported the conclusion that reasonable efforts to calm Ms. Hemmings would likely have succeeded, allowing the surgery to continue without general anesthesia and preventing her injuries.[xi]
Accordingly, the SCC concluded that the necessary counterfactual analysis was already implicit in the trial judge’s findings.[xii] Given the direct connection between Dr. Jamensky’s negligence and the injuries, and the strong supporting evidence, a separate, express explanation of what would have happened had he acted appropriately was redundant.
Conclusion
The SCC’s decision in Hemmings does not introduce a new test for factual causation or remoteness. Rather, its significance lies in clarifying the circumstances in which a trial judge’s application of these established principles may justify appellate intervention.
The contrasting findings concerning Ms. San Juan and Dr. Jamensky demonstrate that an appellate court must distinguish between an insufficiently articulated analysis and a genuine failure to apply the correct legal test.
For parties considering an appeal in a negligence action, Hemmings underscores the importance of identifying an actual legal error rather than simply challenging the trial judge’s assessment of the evidence.
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[i] Hemmings v Padmore, 2026 SCC 34.
[ii] Ibid at para 23.
[iii] Ibid at para 10.
[iv] Ibid at para 20.
[v] Ibid at para 90.
[vi] Ibid at paras 94-95.
[vii] Ibid at paras 91-93.
[viii] Ibid at para 130.
[ix] Ibid at para 152.
[x] Ibid at para 158.
[xi] Ibid at paras 154-156.
[xii] Ibid at paras 157-158.