In the recently published and noteworthy case of Clements v. Clements
, 2012 SCC 32
, the Supreme Court of Canada re-established that the issue of whether an individual caused injury or harm to another individual (cause in fact) is determined by way of the so-called “but for” test. It further confirmed that a “material contribution to risk approach” to these matters is to be reserved for exceptional circumstances where it is required by fairness and conforms to the principles that ground recovery in tort. In particular, the Court held that the material contribution approach, which dispenses with the requirement that the plaintiff prove that a certain act or omission caused his or her injuries, may be used in cases with a number of “tortfeasors” (an individual who commits a wrongful act that injures another) where but for the negligent act of one or more of them the plaintiff would not have been injured.
Robust and Common Sense Material Contribution Test in Personal Injury Claims:
Importantly, and in keeping with its narrowing of the permitted uses of the material contribution approach, the Court emphasized that the but for test is to be applied in a “robust” and “common sense fashion”. Scientific precision is not required:
 On its own, proof by an injured plaintiff that a defendant was negligent does not make that defendant liable for the loss. The plaintiff must also establish that the defendant’s negligence (breach of the standard of care) caused the injury. That link is causation.
 Recovery in negligence presupposes a relationship between the plaintiff and defendant based on the existence of a duty of care — a defendant who is at fault and a plaintiff who has been injured by that fault. If the defendant breaches this duty and thereby causes injury to the plaintiff, the law “corrects” the deficiency in the relationship by requiring the defendant to compensate the plaintiff for the injury suffered. This basis for recovery, sometimes referred to as “corrective justice”, assigns liability when the plaintiff and defendant are linked in a correlative relationship of doer and sufferer of the same harm…
 The test for showing causation is the “but for”test. The plaintiff must show on a balance of probabilities that “but for”the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessaryto bring about the injury ― in other words that the injury would not have occurred without the defendant’s negligence. This is a factual inquiry. If the plaintiff does not establish this on a balance of probabilities, having regard to all the evidence, her action against the defendant fails.
 The “but for” causation test must be applied in a robust common sense fashion. There is no need for scientific evidence of the precise contribution the defendant’s negligence made to the injury…
The Court further affirmed that a trial judge may draw a common sense inference of causation using the but for test. However, it also confirmed that it is open to the defendant to challenge it by calling evidence tending to show that the accident would have happened without his or her negligence:
 A common sense inference of “but for” causation from proof of negligence usually flows without difficulty. Evidence connecting the breach of duty to the injury suffered may permit the judge, depending on the circumstances, to infer that the defendant’s negligence probably caused the loss…
 Where “but for” causation is established by inference only, it is open to the defendant to argue or call evidence that the accident would have happened without the defendant’s negligence, i.e. that the negligence was not a necessary cause of the injury, which was, in any event, inevitable…
Facts of Case & Court Decisions:
In this particular case, the defendant was driving his motorcycle in wet weather, with his wife riding behind on the passenger seat. The bike was about 100 pounds overloaded. Unbeknownst to the defendant driver of the motorcycle, a nail had punctured the rear tire. Though in a 100 km/h zone, the defendant accelerated to at least 120 km/h in order to pass a car; the nail fell out, the rear tire deflated, and the bike began to wobble. The defendant was unable to bring the bike under control and it crashed. As a result of the accident, the defendant’s wife suffered a severe traumatic brain injury. She then sued, alleging that her injury was caused by her husband’s negligence in driving an overloaded bike too fast.
The trial judge found that the defendant’s negligence, in fact, contributed to the injury. However, he also found that the defendant’s wife, through no fault of her own, was unable to prove “but for” causation, due to the limitations of scientific reconstruction evidence. The trial judge applied a material contribution test instead and found the Defendant liable on this basis. The B.C. Court of Appeal set aside the judgment and dismissed the action, on the basis that “but for” causation had not been proved and the material contribution test did not apply.
The Supreme Court of Canada held that the trial judge committed two errors: by insisting on scientific reconstruction evidence as a necessary condition of finding causation, using the but for test, and by applying a material contribution test. The Court held that scientific precision was not necessary to make a determination of the cause of the accident. It further held that the trial judge should not have applied the material contribution approach because the case was a “simpe single-defendant case”. The Court held that a new trial was the appropriate remendy, as it was uncertain whether the trial judge would have found that the defendant’s negligence caused the accident given the errors committed.