The plaintiff must prove that the defendant’s negligence caused his loss. This is known as cause-in-fact. It should not to be confused with the control device remoteness of damage, sometimes known as proximate cause, which may excuse a defendant from liability for loss caused to the plaintiff on the ground of fairness. Cause-in-fact focuses on the factual issue of the sufficiency of the connection between the defendant’s wrongful act and the plaintiff’s loss. It is this connection that justifies the imposition of responsibility on the negligent defendant. That is the issue canvassed here together with some related problems of multiple tortfeasors.
The conventional test to determine cause-in-fact is the but for test. One must ask the question "would the plaintiff’s damage have occurred but for the defendant’s negligence?" If the answer is "no," the defendant’s negligence is a cause-in-fact of the damage. If the answer is "yes," indicating that the damage would have occurred whether or not the defendant was negligent, his negligence is not a cause-in-fact. The test is grammatically awkward but it does have the merit of focusing on the defendant’s role in producing the damage to the exclusion of other legally extraneous causes.
The application of the but for test rarely calls for close or precise analysis. Most frequently, courts merely identify the test and draw a conclusion. It has recently been pointed out, however, that clarity, accuracy, and certainty are enhanced by recognizing that the application of the but for test involves a number of discrete steps.61First, the harm that is alleged to have been caused by the defendant must be identified. Second, the specific act or acts of negligence by the defendant must be isolated. Third, the trier of fact must mentally adjust the facts so that the defendant’s conduct satisfies the standard of care of the reasonable person, being sure to leave all other facts the same. Fourth, it must be asked if the plaintiff’s harm would have occurred if the defendants had been acting with reasonable care. The fifth step is to answer the question.
The burden of proof in respect of cause-in-fact is on the plaintiff. The trier of fact must be persuaded that the defendant’s negligence probably caused the plaintiff’s loss. Courts have warned against sheer
speculation, theorizing, and guessing, but there is always some degree of speculation in determining cause-in-fact. It is inevitably a hypothetical inquiry. One can never be assured of what would have happened if the defendant had exercised reasonable care. The trier of fact is assisted by the evidence of the circumstances of the accident, but ultimately, the determination of cause-in-fact depends upon a generous application of common sense, experience, and intuition.
The operation of the but for test is usefully illustrated by two contrasting American decisions. In Marek v. Southern Enterprises, Inc.62some unknown persons began throwing firecrackers around a movie theatre. Several minutes after this began, one of the firecrackers exploded close to the plaintiff’s head, causing him a loss of hearing in one ear. The defendant owner of the theatre was found negligent for failing to deal with this dangerous situation more promptly. The Court was also persuaded that, if the defendant had immediately turned on the lights and interrupted the movie, the plaintiff’s injury would not have occurred. The but for test was satisfied. The opposite conclusion was drawn in East Texas Theatres, Inc. v. Rutledge.63The plaintiff was hit in the head by a bottle when she was leaving the defendant’s movie theatre at the end of the show. The bottle was thrown from the balcony by some unidentified person. During the performance of the movie, there had been a good deal of rowdiness in the theatre and paper cups had been thrown about. The jury found that the defendant was negligent. He ought to have intervened and ejected the rowdy persons. In its opinion, the bottle would not have been thrown if he had taken these steps. The Texas Court of Appeal disagreed. In its view, it had not been established on the balance of probabilities that the bottle thrower was one of the rowdy persons who would have been ejected if due care had been taken. The injury, therefore, might have occurred even if such steps had been taken. An alternative argument that some timely and lesser measures of crowd control would have prevented the bottle-throwing incident was dismissed by the Court as purely speculative.
It is not necessary to prove that the defendant’s negligence was the sole cause or the predominant cause of the plaintiff’s damage. There may be a number of causes both tortious and non-tortious. So long as the defendant’s act is a cause of the plaintiff’s damage, the defendant is fully liable for that damage. The Supreme Court decision in Athey v. Leonati64is illustrative. The plaintiff, who had a long history of back prob-
lems, suffered back injuries as a result of the defendants’ negligence. In the course of his rehabilitation, he suffered a herniated disc. The trial judge found that his herniated disc was caused by a combination of the pre-existing problems and the defendants’ negligence. In her view, the defendants’ negligence was 25 percent responsible for the herniated disc and she awarded 25 percent of her assessment of the plaintiff’s damages. The Supreme Court held that this was incorrect. On the balance of probabilities, the trial judge had found that the defendants’ negligence was a cause of the loss and consequently the defendants were 100 percent liable for that loss.
The but for test has proved to be an effective one in determining cause-in-fact but there are circumstances where it is unworkable and leads to clear injustice. The classic example is where two defendants negligently light separate fires, each of which is sufficient to spread and destroy a neighbour’s premises. The fires, however, converge and a single conflagration destroys the premises. Application of the but for test sequentially to each of the defendants results in each defendant being exonerated because the loss would still have occurred if either one, but not both, had been careful. Clearly, in fairness, both defendants should be held responsible. To achieve this result the courts developed the material contribution test. Under this test the conduct of both defendants is regarded as a cause-in-fact because it materially contributed to the loss.
In the latter part of the twentieth century, there was a good deal of debate about cause-in-fact and the sufficiency of the but for test to handle sophisticated medical malpractice cases; "toxic torts" cases dealing with the negligent testing, manufacture, and distribution of products and compounds that are suspected of causing cancer or other illnesses; and cases dealing with the exposure of persons to illness-causing micro-organisms. These are situations where the plaintiff may be able to prove that the defendant was negligent and that the harm she suffered was within the scope of the risk created by the defend-ant’s negligence, but she cannot prove a causal link on the balance of probabilities. It was argued that in such cases it was appropriate to ease the conventional burden of proof on the plaintiff by applying an augmented risk theory. An augmented risk rule would require a plaintiff to prove that the defendant was negligent and that the harm suffered by the plaintiff was within the scope of the risk created by the defendant’s negligence. This would be sufficient to establish a prima facie case of cause-in-fact and liability would be imposed unless the defendant was able to prove on the balance of probabilities that his conduct was not a cause-in-fact of the plaintiff’s loss.
The augmented risk theory was considered by the House of Lords in MCGHEE v. National Coal Board.65In that case the plaintiff worker suffered dermatitis as a consequence of working in dusty brick kilns. There was no negligence in having a dusty work site. The only negligence was in failing to provide the worker with adequate shower facilities to remove the dust at the end of his shift. The expert scientific/medical evidence could not determine if the delay in removing the dust caused the dermatitis. All that could be said was that exposure to dust increased the risk of getting dermatitis. A majority of the House of Lords held that in these circumstances, a material increase in the risk of the disease may be equated with a material contribution to the disease, and it concluded that the defendant’s act was a cause of the dermatitis. Lord Wilberforce, however, was willing to go further and more fully embrace an augmented risk theory. In his view, proof by the plaintiff that the defendant was negligent, coupled with proof that the plaintiff’s loss was within the scope of the risk created by the defendant’s negligence, was sufficient to reverse the burden of proof of causation. To escape liability, the defendant would have to prove on the balance of probabilities that the lack of washing facilities was not a cause of the dermatitis. MCGHEE gave rise to a sustained academic and judicial debate about cause-in-fact and the scope and merit of an augmented risk rule. The Canadian courts initially embraced Lord Wilberforce’s approach in Mc-Ghee but they became more ambivalent about it when the House of Lords insisted in Wilsher v. Essex Area Health Authority66that no new principle of law had been established in MCGHEE. It was construed as no more than a robust and pragmatic application of conventional cause-in-fact principles. Eighteen years after MCGHEE, the Supreme Court joined the debate in Snell v....