1) Cause-in-Fact

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. [Note 55: This step-by-step process is outlined by D.W. Robertson, "The Common Sense of Cause in Fact" (1997) 75 Tex. L. Rev. 1765 at 1769-73.] First, 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. [Note 56: 99 S.W.2d 594 (Tex. Comm'n App. 1936).] some 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. [Note 57: 453 S.W.2d 466 (Tex. 1970).] The 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. Leonati [Note 58: [1996] 3 S.C.R. 458.] is illustrative. The plaintiff, who had a long history of back problems, 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 breaks down and leads to clear injustice. This has arisen, for example, in situations of multiple sufficient causes. The classic example is that of two defendants negligently lighting fires, each of which is sufficient, independently, to cause the plaintiff's loss. 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 or substantial connection test. Under this test the conduct of both defendants is regarded as a cause-in-fact because it materially contributed to the loss.

The material contribution test has sometimes been used in situations where the but for test is not productive of a clearly erroneous or unfair result. It has been expressed as a permissible alternative to the but for test. Judicial statements that the defendant must cause or materially contribute to the plaintiff's loss are not uncommon. Technically, there does not seem to be any advantage to be gained by using the material contribution test in substitution of the but for test. It may, however, be advantageous in practice to use it because the concept is sufficiently vague and imprecise to permit a lowering of the cause-in-fact hurdle when judicial intuition and a sense of fairness suggest that the defendant should be held liable for the damage. [Note 59: See Klar, above note 41 at 323.] The contribution must, nevertheless, still be substantial and significant to qualify as a cause-in-fact. Insubstantial or insignificant contributions to the damage are often described as de minimis.

In the past few decades, there has been some dissatisfaction with the conventional causation rules and the burden of proof. This has arisen most often in respect of medical malpractice cases and claims arising out of the testing, manufacture, and distribution of toxic products and compounds that are suspected of causing cancer and other illnesses. In these kinds of cases, proof of causation presents special difficulties for plaintiffs and some courts have proposed modifications of the conventional causation rules to ease their burden of proof. The most provocative decision of this kind is McGhee v. National Coal Board. [Note 60: (1972), [1973] 1 W.L.R. 1 (H.L.). ] In that case, a majority of the House of Lords held that in some circumstances a material increase in the risk of injury may be equated to a material contribution to the injury sufficient to establish cause-in- fact. Lord Wilberforce was willing to go even further. 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 that made the defendant's conduct negligent, was sufficient to reverse the burden of proof of causation. To escape liability, the defendant must prove that his negligence was not a cause of the loss. Canadian courts were initially quite receptive to the general policy direction of McGhee and applied Lord Wilberforce's principle in a number of cases. The issue was not addressed by the Supreme Court until the case of Snell v. Farrell, [Note 61: [1990] 2 S.C.R. 311.] some eighteen years after McGhee. Ironically, by that time McGhee had fallen into disfavour in England. [Note 62: See Wilsher v. Essex Area Health Authority, [1988] A.C. 1074 (H.L.).]

In Snell, the defendant surgeon continued cataract surgery on the plaintiff in spite of the fact that an anaesthetizing injection had caused some bleeding behind her eye. The prudent course of action was to discontinue the surgery. Bleeding threatens the optic nerve and a continuation of the surgery could exacerbate the bleeding and increase the risk of damaging the patient's sight. Some months later it was discovered that the plaintiff had lost her sight in that eye. At the trial, the medical experts were unable to give a firm opinion that the nerve damage was caused by a continuation of the surgery. It may have resulted from natural causes, including the plaintiff's high blood pressure or her diabetes. The plaintiff argued that the defendant's negligent act had certainly increased the risk of damage to the optic nerve and the loss of sight was within the scope of that risk. The lower courts found for the plaintiff on the basis of McGhee. The Supreme Court upheld that decision but did not adopt the McGhee approach. In a unanimous decision, the Court reasserted the conventional causation rules and the traditional burden of proof. The Court was not convinced that a change in the law was necessary. In its view, the traditional rules had not prevented plaintiffs with valid claims from proving their cases. Furthermore, the adoption of McGhee would create the risk of defendants being held responsible for loss that they had not in fact caused. It might also lead to an undesirable increase in medical liability, placing pressure on the liability insurance system. The Court, however, emphasized that causation rules must not be applied in a strict or rigid manner; it called for a flexible, pragmatic, and common-sense approach. It also noted that, where facts lie particularly within the knowledge of the defendant, little affirmative evidence of cause-in-fact is required of the plaintiff and, in the absence of evidence to the contrary, it is fair to make an inference of cause-in-fact. It is not appropriate, however, to reverse the burden of proof. The ultimate burden remains on the plaintiff. The Court also addressed the issue of expert evidence in medical malpractice cases. It is not necessary to secure a firm expert opinion in favour of the plaintiff's assertion of cause. Medical experts tend to speak in terms of scientific certainty rather than the lower standard of the balance of probabilities favoured by tort law. In the Court's view, the plaintiff had presented sufficient evidence to permit an inference of causation to be drawn.

Since Snell, the language of decision making has changed. The courts no longer use the language of presumptions or reversing the burden of proof. Now reference is made to the terminology used in Snell, including the propriety of drawing inferences of causation and the need to take a pragmatic and common-sense approach to the question of cause-in-fact. The patterns of decision making do not, however, seem to have been substantially affected by Snell. The gradual easing of the burden of proof sparked by McGhee continues. In the recent case of Webster v. Chapman, [Note 63: (1997), 155 D.L.R. (4th) 82 (Man. C.A.).] for example, a physician was held liable for failing to terminate promptly a woman's medication (coumedin) when she became pregnant. The medication created a material risk to the fetus, a risk that materialized and damaged her child. The Court equated the material increase in risk of birth defect with a material contribution to the plaintiff's injuries.

It should also be noted that the assertion of traditional causation principles in Snell does not foreclose their future modification. The Court observed that causation principles are not immutable and are subject to change to reflect societal needs and justice. The Court has recognized certain exceptions in the past and a number of special challenges lie ahead. Some are canvassed below.

2) Alternative Liability

In Cook v. Lewis, [Note 64: [1951] S.C.R. 830.] the Supreme Court adopted the American principle of alternative liability. It applies where it is clear that only one of a small number of negligent persons caused the plaintiff's loss, but the plaintiff is unable to establish which person it was. If all the negligent persons are joined as defendants, the burden of proof of causation is reversed and each defendant is held jointly and severally liable (each defendant is fully liable for the plaintiff's losses) unless he can establish on the balance of probabilities that he did not cause the loss to the plaintiff. In Cook, for example, two hunters fired simultaneously in the direction of the plaintiff. The plaintiff was hit by a single bullet. Both hunters were clearly negligent but the plaintiff was unable to prove which of them shot him. Each hunter claimed that the other caused the injury. The requirements of alternative liability were met and, in the absence of exonerating evidence from either one of them, they were held jointly and severally liable. Alternative liability is normally justified on the grounds that all of the defendants are wrongdoers, they normally have better information of the circumstances of the accident than the plaintiff, they may have impaired the plaintiff's power to prove cause-in-fact, and, given the small number of defendants, there is a high likelihood that any one of them caused the loss. [Note 65: There are some indications that the principle of alternative liability will be kept on a tight rein. It has been suggested, for example, that it may not apply where the plaintiff has been guilty of contributory negligence: see Lange v. Bennett, [1964] 1 O.R. 233 (H.C.J.).]

3) Joint Tortfeasors (Concerted Action)

In some circumstances, a number of people may be responsible for the single tortious act of one of them. In those circumstances, proof of a single tort suffices to establish liability against them all. Broadly speaking, this arises where the defendants have some special relationship or they participate in a common venture or joint enterprise involving tortious conduct. These defendants are known as joint tortfeasors and they are jointly and severally liable for the plaintiff's loss.

There are four categories of joint tortfeasors. First, one who instigates or encourages another to commit a tort and the person who commits it are joint tortfeasors. Second, an employer and an employee are joint tortfeasors in respect of a tort committed by the employee within the scope of his employment. Third, a principal and agent are joint tortfeasors in respect of torts committed by the agent within the actual or apparent authority of the agent. Fourth, there is a residual fact- specific category covering other instances of concerted action by two or more involving the commission of a tortious act. The basis of joint responsibility in this residual category is guilt by participation, not guilt by association. The hunters in Cook v. Lewis, for example, were not joint tortfeasors. It was a case of independent and parallel tortious conduct. That situation may be contrasted with those of a driver of a towed vehicle and the driver of the vehicle doing the towing, who were held to be joint tortfeasors in respect of damage arising from safety violations in the towed vehicle, [Note 66: Harpe v. Lefebvre (1976), 1 C.C.L.T. 331 (Alta. Dist. Ct.).] and highway workers who were held to be joint tortfeasors when they threw sand at a passing bus and thereby injured the eye of a passenger who was sitting by an open window. [Note 67: Beecham v. Henderson & Houston, [1951] 1 D.L.R. 628 (B.C.S.C.).]