A case brought before the Supreme Court of Canada demonstrates the possibility of successfully using the “but for” test to prove causation.


A husband was driving his motorcycle in wet weather with his wife seated in the back. A nail punctured the rear tire and the bike was 100 pounds overloaded when it spun out of control. The wife suffered a traumatic brain injury, alleging that her injury was caused by the husband’s negligence in driving the overloaded bike at too high a speed. 


The trial judge found the husband was negligent, contributing to the injury. However, the trial judge also found that the wife was not able to prove “but for” causation. Applying a material contribution test, the husband was found liable. 

Once brought before the Court of Appeal, the judgment was set aside and the action was dismissed. In this decision, the Court of Appeal held that the “but for” causation was not proven and the material contribution test was not applicable.  Thus, the appeal was allowed, as well as a new trial was to be ordered but with the proper application of “but for” causation. 

Material contribution to the risk of injury occurs when it is not possible to determine which of a number of negligent acts, by multiple actors, actually caused the injury but it is established that at least one of them did in fact cause it. This substitutes the “but for” causation for proof of material contribution of risk, imposing liability because the act itself contributed to the risk that injury would occur. 

The plaintiff cannot successfully bring the claim unless she is able to show as a matter of fact that she would not have suffered her loss “but for” the negligent act of her husband. 

 Read the full case here

MedMalDoctors provides expert evidence-based opinions on Causation and Standard of Care regarding potential Medical Malpractice. To learn more about how MedMalDoctors can assist you in your next Medical Malpractice case, call us at 1.800.590.9631 or send an email to marketing@medmaldoctors.ca

From CanLii