The SCC on Causation in Fact
In an earlier blog post we discussed the four elements a plaintiff must prove in a negligence action. Causation is the last of these four elements. After identifying an allegedly negligent act, the plaintiff must prove that harm flowed from that act. There are two types of causation that the plaintiff must establish: factual causation and legal causation. This blog post will focus on the former.
In order to establish factual causation, the plaintiff must show that “but for” the negligent act or omission, the plaintiff’s injuries would not have occurred. In Athey v Leonati,  3 SCR 458, a leading case on factual causation, the Supreme Court of Canada (SCC) held that causation is established when the defendant’s act or omission causes or contributes to the injury in a material way. This means that the defendant does not need to be the sole cause of the injury, but merely part of the cause.
The SCC has considered factual causation on a number of occasions over the years. The foundational case on causation in a medical malpractice action is Snell v Farrell,  2 SCR 311, in which the Court endorsed a robust and pragmatic approach to causation meaning that a court may draw an inference of causation using a common sense approach to the facts even if scientific proof has not been adduced. This is especially important in medical malpractice cases. As noted by Sopinka J in Snell, medical experts often think of causation in terms of scientific certainty which is a much more stringent standard that the balance of probabilities standard required by the law (51%).
The inference of causation has been the subject of much jurisprudence in recent years. In Clements v Clements, 2012 SCC 32, the SCC reaffirmed that the “but for” test is to be applied in a common sense fashion and that while the ultimate evidentiary burden remains with the plaintiff, it is permissible for the court to draw an inference of causation in the absence of scientific proof. In Ediger v Johnston, 2013 SCC 18, the SCC held that the court may draw an inference of causation against a defendant who does not adduce sufficient evidence contrary to the plaintiff’s theory. In St-Germain v Benhaim, 2016 SCC 48, the SCC confirmed that the courts are permitted but not required to draw an inference of causation in the absence of positive scientific proof.
The ability of the court to draw an inference of causation may be especially important in the context of a negligent omission. In such cases, the allegation is that the defendant failed to do something he or she ought to have done. It is the plaintiff’s burden to prove what would have happened but for the defendant failing to do same. Click here to read more about how the courts approach causation in these cases.
Written by Iman Jomha