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The Basic Rule of Recovery for Negligence

January 7, 2022

British Columbia

,

Canada

Issue

Is the material contribution test still applied in cases involving dependency causation?

Conclusion

The basic rule of recovery for negligence is that the plaintiff must establish on a balance of probabilities that the defendant caused the plaintiff’s injury on the “but for” test. This is a factual determination. Exceptionally, however, courts have accepted that a plaintiff may be able to recover on the basis of “material contribution to risk of injury”, without showing factual “but for” causation. This can occur in cases where it is impossible to determine which of a number of negligent acts by multiple actors in fact caused the injury, but it is established that one or more of them did in fact cause it. (Clements v. Clements)

In Clements (Litigation Guardian of) v. Clements, the British Columbia Court of Appeal ruled that a judge can resort to the material-contribution test in only two situations: ones involving circular causation and dependency causation. Dependency causation involves factual situations where it is impossible for the plaintiff to prove if a third party would have taken some action in the face of a defendant’s negligence and such third party’s action would have facilitated harm to the plaintiff. The Court concluded that the “but for” test rarely fails, and should be applied only in situations involving circular causation and dependency causation. If the “but for” test fails, the plaintiff must meet two pre-conditions to utilize the material contribution test for causation:

1) It must be impossible for the plaintiff to prove causation (either due to circular or dependency causation); and,

2) The plaintiff must be able to prove that the defendant breached the standard of care, exposed the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that type of injury.

On appeal to the Supreme Court in Clements v. Clements, the Supreme Court clarified the law of causation in Canada. The Court concluded as a general rule, a plaintiff cannot succeed unless she shows as a matter of fact that she would not have suffered the loss “but for” the negligent act or acts of the defendant. A trial judge is to take a robust and pragmatic approach to determining if a plaintiff has established that the defendant’s negligence caused her loss. Scientific proof of causation is not required. Exceptionally, a plaintiff may succeed by showing that the defendant’s conduct materially contributed to risk of the plaintiff’s injury, where:

(a) the plaintiff has established that her loss would not have occurred “but for” the negligence of two or more tortfeasors, each possibly in fact responsible for the loss; and

(b) the plaintiff, through no fault of her own, is unable to show that any one of the possible tortfeasors in fact was the necessary or “but for” cause of her injury, because each can point to one another as the possible “but for” cause of the injury, defeating a finding of causation on a balance of probabilities against anyone.

The Court stated that the British Columbia Court of Appeal reached a similar view of the law and that it correctly identified the critical element to the application of a material contribution to risk approach — the impossibility of proving which of two or more possible tortious causes is in fact the cause of the injury. However, the Supreme Court stated that it was unnecessary to hang the analysis on “circular causation”, and “dependency causation”, which might complicate the matter rather than simplify it.

Clements v. Clements is the leading authority on the relationship between the “but for” test and liability on the basis of material contribution to risk. In that decision, the Supreme Court explained that “but for” causation and material contribution to risk are different concepts and that the latter is not a test of causation at all. Rather, it is a policy-driven rule of law aimed at avoiding situations where denying liability would offend notions of fairness and justice. (Saskatchewan Government Insurance v Schira)

No decision since the Supreme Court's ruling in Clements v. Clements was identified which considered the concept of "dependency causation" in deciding whether to apply the material contribution test.

Law

In Resurfice Corp. v. Hanke, [2007] 1 SCR 333, 2007 SCC 7 (CanLII)("Resurfice"), the Supreme Court of Canada reaffirmed the "but for" test as the primary test for determining causation. McLachlin C.J., in stating the general principles that apply to the determination of causation, said:

[21] First, the basic test for determining causation remains the “but for” test. This applies to multi-cause injuries. The plaintiff bears the burden of showing that “but for” the negligent act or omission of each defendant, the injury would not have occurred. Having done this, contributory negligence may be apportioned, as permitted by statute.

[22] This fundamental rule has never been displaced and remains the primary test for causation in negligence actions. As stated in Athey v. Leonati, at para. 14, per Major J., “[t]he general, but not conclusive, test for causation is the ‘but for’ test, which requires the plaintiff to show that the injury would not have occurred but for the negligence of the defendant”. Similarly, as I noted in Blackwater v. Plint, at para. 78, “[t]he rules of causation consider generally whether ‘but for’ the defendant’s acts, the plaintiff’s damages would have been incurred on a balance of probabilities.”

[23] The “but for” test recognizes that compensation for negligent conduct should only be made “where a substantial connection between the injury and the defendant’s conduct” is present. It ensures that a defendant will not be held liable for the plaintiff’s injuries where they “may very well be due to factors unconnected to the defendant and not the fault of anyone”: Snell v. Farrell, at p. 327, per Sopinka J.

McLachlin C.J. explained that in “special circumstances” it will be appropriate to depart from the "but for" test and make the causation determination under the material contribution test. The material contribution test applied where it was impossible due to factors outside the plaintiff's control to prove causation using the "but for" test. In addition, it had to be clear that the defendant breached a duty of care owed to the plaintiff:

[24] However, in special circumstances, the law has recognized exceptions to the basic “but for” test, and applied a “material contribution” test. Broadly speaking, the cases in which the “material contribution” test is properly applied involve two requirements.

[25] First, it must be impossible for the plaintiff to prove that the defendant’s negligence caused the plaintiff’s injury using the “but for” test. The impossibility must be due to factors that are outside of the plaintiff’s control; for example, current limits of scientific knowledge. Second, it must be clear that the defendant breached a duty of care owed to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that form of injury. In other words, the plaintiff’s injury must fall within the ambit of the risk created by the defendant’s breach. In those exceptional cases where these two requirements are satisfied, liability may be imposed, even though the “but for” test is not satisfied, because it would offend basic notions of fairness and justice to deny liability by applying a “but for” approach.

[26] These two requirements are helpful in defining the situations in which an exception to the “but for” approach ought to be permitted. Without dealing exhaustively with the jurisprudence, a few examples may assist in demonstrating the twin principles just asserted.

[27] One situation requiring an exception to the “but for” test is the situation where it is impossible to say which of two tortious sources caused the injury, as where two shots are carelessly fired at the victim, but it is impossible to say which shot injured him: Cook v. Lewis, 1951 CanLII 26 (SCC), [1951] S.C.R. 830. Provided that it is established that each of the defendants carelessly or negligently created an unreasonable risk of that type of injury that the plaintiff in fact suffered (i.e. carelessly or negligently fired a shot that could have caused the injury), a material contribution test may be appropriately applied.

[28] A second situation requiring an exception to the “but for” test may be where it is impossible to prove what a particular person in the causal chain would have done had the defendant not committed a negligent act or omission, thus breaking the “but for” chain of causation. For example, although there was no need to rely on the “material contribution” test in Walker Estate v. York Finch General Hospital, this Court indicated that it could be used where it was impossible to prove that the donor whose tainted blood infected the plaintiff would not have given blood if the defendant had properly warned him against donating blood. Once again, the impossibility of establishing causation and the element of injury-related risk created by the defendant are central.

In Clements (Litigation Guardian of) v. Clements, 2010 BCCA 581 (CanLII), the issue was whether the trial judge had erred by applying the material contribution test on the issue of causation in a motor vehicle accident claim. The plaintiff was injured while riding as a passenger on a motorcycle driven by her husband, the defendant. The defendant pulled out to pass a vehicle when his rear tire was punctured by an unknown small object on the road. He lost control and the motorcycle flipped over, throwing both rider and passenger off the bike. The trial judge determined that the defendant was negligent since he was driving too fast and the bike was overloaded. However, the judge was not satisfied on a balance of probabilities that, "but for" the excessive speed and excessive weight, the motorcycle would not have capsized in any event. Since it was impossible to determine the combination of speed and weight at which the defendant would have been able to regain control of the motorcycle and bring it to a safe stop, the trial judge turned to the material contribution test. Under this test, the defendant was liable. The Court of Appeal ruled that the trial judge should have dismissed the plaintiff's action once he found that causation could not be established under the "but for" test:

[39] In my view, once the trial judge found that Mrs. Clements had failed to prove causation under the but-for test, he should have dismissed her action. This is not a case that permits causation being decided on another basis.

[40] Causation is a fundamental element of liability for negligence. A person who suffers harm is entitled to compensation from those who caused that harm. The but-for test is the method by which factual causation is established. The way the test works is described in Linden and Feldthusen, Canadian Tort Law, 8th ed. (Markham, Ont.: LexisNexis Butterworths, 2006) at 116:

[I]f the accident would not have occurred but for the defendant’s negligence, this conduct is a cause of the injury. Put another way, if the accident would have occurred just the same, whether or not the defendant acted, this conduct is not a cause of the loss. Thus the act of the defendant must have made a difference. If the conduct had nothing to do with the loss, the actor escapes liability.

[Emphasis added.]

[41] In Cork v. Kirby McLean, Ltd., [1952] 2 All E.R. 402 at 407 (C.A.), Lord Denning (as he then was) stated the test as follows:

Subject to the question of remoteness, causation is, I think, a question of fact. If you can say that the damage would not have happened but for a particular fault, then that fault is in fact a cause of the damage; but if you can say that the damage would have happened just the same, fault or no fault, then the fault is not a cause of the damage. It often happens that each of the parties at fault can truly say to the other: “But for your fault, it would not have happened.” In such a case both faults are in fact causes of the damage.

[Emphasis added.]

The Court reviewed Resurfice and stated the "but for" test was the default test for determining causation. The Court clarified that the material contribution provides a basis for legal and not factual causation:

[45] It is important to keep in mind that the material-contribution test discussed in Resurfice Corp. is not a test for determining factual causation. It does not provide a framework for determining whether a plaintiff has proven on a balance of probabilities that a defendant’s negligence has in fact caused harm. Rather, it provides a basis for finding legal causation when there is a possibility that the defendant’s negligent actions could have been a factual cause.

[46] In Chambers v. Goertz, 2009 BCCA 358, 96 B.C.L.R. (4th) 236, Mr. Justice K. Smith discussed the fact that the use of the material-contribution test leads to the finding of a legal, as opposed to a factual, connection between a defendant’s negligence and the harm suffered by a plaintiff:

[17] In the passages from Resurfice Corp. v. Hanke, to which Mr. Ahmad refers, Chief Justice McLachlin, writing for the Court, used the phrase in connection with cases in which it is impossible for the plaintiff to prove a causal link between the breach of duty and the harm, such as where the explication of the causal link is beyond the limits of current scientific knowledge (Fairchild v. Glenhaven Funeral Services Ltd., [2002] UKHL 22, [2002] 3 All E.R. 305; Barker v. Corus (UK) Plc., [2006] UKHL 20, [2006] 2 A.C. 572 – cases in which the defendants’ breach of duty materially increased the risk of harm but it was not possible to prove a causal connection to the harm itself); where it is impossible to prove which of two simultaneous acts by two negligent actors caused the loss (Cook v. Lewis, 1951 CanLII 26 (SCC), [1951] S.C.R. 830, [1952] 1 D.L.R. 1); and where it may be impossible to prove what a third party, whose conduct was a “but for” cause of the loss, would have done absent the defendant’s careless conduct (Walker Estate v. York Finch General Hospital, 2001 SCC 23, [2001] 1 S.C.R. 647, 198 D.L.R. (4th) 193). As this Court noted in Sam v. Wilson, 2007 BCCA 622, 78 B.C.L.R. (4th) 199 at para. 109, 249 B.C.A.C. 228, this use of “material contribution” does not signify a test of causation at all; rather it is a policy-driven rule of law designed to permit plaintiffs to recover in such cases despite their failure to prove causation. In such cases, plaintiffs are permitted to “jump the evidentiary gap”: see “Lords a’leaping evidentiary gaps”, (2002) Torts Law Journal 276, and “Cause-in-Fact and the Scope of Liability for Consequences”, (2003) 119 L.Q.R. 388, both by Professor Jane Stapleton. That is because to deny liability “would offend basic notions of fairness and justice”: Resurfice Corp. v. Hanke, para. 25.

[Underlining in original; bold added.]

[47] Although the discussion of the material-contribution test in Resufice Corp. is obiter dicta—the appeal was allowed on the basis that the Court of Appeal should not have interfered with the finding of the trial judge that the manner in which the plaintiff was injured was not reasonably foreseeable—the Supreme Court of Canada clearly intended to provide guidance with respect to the issue of causation. Accordingly, what it said must be accepted as authoritative in that regard: Reilly v. Canada (Attorney General), 2008 BCCA 167, 77 B.C.L.R. 230 at paras. 69, 70, applying R. v. Henry, 2005 SCC 76, [2005] 3 S.C.R. 609.

[48] However, I do not read Resurfice Corp. as supporting resort to the material-contribution test whenever a defendant’s negligence has materially increased a plaintiff’s risk of injury and it is impossible for the plaintiff to prove that that negligence was a factual cause of the injury. To do so would substantially alter the existing law and would have the effect of displacing but-for as the primary test for determining causation. It is only in exceptional circumstances that resort to the material-contribution test will, as a matter of policy, be appropriate.

The Court of Appeal agreed with the academic opinion of Professor Erik Knutsen that a judge can resort to the material contribution test in only two situations: what the professor referred to as circular causation and dependency causation. Dependency causation is where proof of factual causation depends on establishing what one party would have done if another party had not acted in a negligent manner, something which may be impossible to prove:

[54] The question of when it will be appropriate to resort to the material-contribution test discussed in Resurfice Corp. has been the subject of some appellate consideration and considerable academic writing. In my view, the answer to this question is fully and articulately set out in a paper by Professor Erik S. Knutsen entitled “Clarifying Causation in Tort”, found at (2010), 33 Dal. L.J. 153. Professor Knutsen’s view, with which I agree, is that a judge can resort to the material-contribution test in only two situations: what he refers to as ones involving circular causation and dependency causation. In all other cases, causation must be determined on the but-for test.

[55] Cook is an example of circular causation. The but-for test makes it impossible to determine which of two negligent parties caused the damage suffered by the plaintiff: as it is just as likely to have been A, it is impossible to show, on a balance of probabilities that it was B, and vice-versa. As Professor Knutsen said (at 164):

The Supreme Court’s words in Hanke are likely trying to express that, in instances where there is complete circular logic which makes the “but for” test unanswerable, like in cases where it is impossible to prove which one of two or more tortious sources caused the plaintiff’s injury, one can reach for the material contribution test to find causation. It is a question not of “how much” but of “which one.” The Supreme Court is not saying, however, that the material contribution test applies to any case where there is more than one tortfeasor. That was the mistake previous courts kept committing. Rare is the case where a fact scenario with multiple tortfeasors requires the material contribution test. McLachlin C.J.C.’s example of Cook v. Lewis is likely trying to communicate that, in instances of “circular causation,” where the “but for” test produces an endless circular answer that is unsatisfactory because one potential causal source is certainly a cause of harm, one can use the material contribution test as long as both pre-conditions are met.

[Emphasis added.]

[56] Walker Estate is an example of dependency causation, where proof of factual causation depends on establishing what one party would have done if another party had not acted in a negligent manner, something which may be impossible to prove. In this regard, Professor Knutsen states (at 164):

The second example in Hanke where the material contribution test is suitable to use involves a chain of multi-party actions, each depending on the other, in a situation of “dependency causation.” The “but for” test may be impossible to prove when one must determine what a party would have done had the defendant not been negligent, and thus how that party’s decision affects the plaintiff’s resulting injury. The example the Court gives is Walker v. York Finch Hospital, a case where it may have been impossible to prove “but for” causation. In that case, it may have been impossible to prove that, but for the negligent screening of blood donors by the defendant blood collection service, a person with HIV-infected blood may not have donated the infected blood which eventually injured the plaintiff. The causal link between the at-fault defendant and the injured plaintiff is thus mediated by the action of a third party. This “dependency causation” necessarily relies on evidence of causation beyond the relationship between the at-fault defendant and the injured plaintiff, and is potentially very difficult to obtain.

[Footnotes omitted, emphasis added.]

The Court of Appeal accepted that the material contribution test should be limited for rare cases, like dependency causation:

[58] In explaining why the material-contribution test should be reserved for rare cases involving logical impossibilities, Professor Knutsen said (at 167):

“But for” works when there is enough evidence to prove, on a balance of probabilities, that the defendant’s breach of the standard of care was a cause of the plaintiff’s injury. The reverse is also true. “But for” works when there is insufficient evidence to prove, on a balance of probabilities, that the defendant’s breach of the standard of care was not a cause of the plaintiff’s injury. The logical answer, whether in favour of the plaintiff or defendant, is usually the result. The material contribution test is not a solution for evidentiary insufficiency. Plaintiffs must still prove causation on a balance of probabilities. The only instances “but for” does not work are in instances where there is insufficient evidence to prove “but for” causation and there is either circular or dependency causation.

[Emphasis in original.]

[59] Perhaps of more importance in the context of the case at bar is Professor Knutsen’s discussion of the impossibility requirement and the reference in Resurfice Corp. to the “current limits of scientific knowledge”. As he points out, our knowledge of science is ever-increasing. What is provable today may not have been provable last year; what cannot be proven today may be provable next year. That forensic science is not always able to provide an answer to a causation question is not a reason for doing away with causation as an essential element of a plaintiff’s case. In this regard, Professor Knutsen said this (at 171):

“Current limits of scientific knowledge” should not be read out of context to mean that the material contribution test is appropriate in any case where the science involved is difficult, complex, or “just not there yet.” Frankly, that is just about any case where personal injury is involved. The science of medicine as it relates to the interaction of disease, medication, and trauma on the body is more of an art than a science. It is constantly evolving. Indeed, one might argue it will always have current limits that soon get eclipsed by future, unknowable limits. But the Supreme Court’s statement is nothing more than an example of one reason why there may be a logical impossibility in proving causation with the “but for” test. It is an explanatory reason, so to speak, for the existence of circular causation. It is not a reason to turn to the material contribution test. It is certainly not a gatekeeper for the material contribution test. The gatekeeping function is met by the two pre-conditions which must be satisfied in instances of circular or dependency causation.

The Court concluded that when the "but for" test fails, the plaintiff must meet two pre-conditions to utilize the material contribution test for causation, including situations of dependent causation. The case before the Court did not involve dependent causation and therefore the judge was wrong to have applied the material contribution test:

[63] In summary, having regard to the over-arching policy that the material-contribution test is available only when a denial of liability under the but-for test would offend basic notions of fairness and justice, I agree with the following statement made by Professor Knutsen in setting out his conclusions (at 187):

g) The “but for” test rarely fails, and currently only in situations involving circular causation and dependency causation:

1) Circular causation involves factual situations where it is impossible for the plaintiff to prove which one of two or more possible tortious causes are the cause of the plaintiff’s harm;

2) Dependency causation involves factual situations where it is impossible for the plaintiff to prove if a third party would have taken some action in the face of a defendant’s negligence and such third party’s action would have facilitated harm to the plaintiff;

h) If the “but for” test fails, the plaintiff must meet two pre-conditions to utilize the material contribution test for causation:

1) It must be impossible for the plaintiff to prove causation (either due to circular or dependency causation); and,

2) The plaintiff must be able to prove that the defendant breached the standard of care, exposed the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that type of injury.

[64] What does this mean for the present case? It means that once the trial judge determined that Mrs. Clements had failed to establish that the motorcycle would not have capsized but for Mr. Clements’s negligence, he should have found that causation had not been proven. This is not a case involving either circular or dependency causation. Rather, it is a case like many others in which, given the current state of knowledge, it is not possible to prove whether the negligent actions of a defendant caused harm. I do not consider it either unfair or unjust, or, to use the words of Professor Knutsen (at 172), “just plain wrong” not to fix Mr. Clements with liability when Mrs. Clements has been unable to show factually that his negligence was a cause of her damages.

In Clements v. Clements, [2012] 2 SCR 181, 2012 SCC 32 (CanLII) ("Clements"), a majority of the Supreme Court allowed an appeal of the Court of Appeal's decision and ordered a new trial. McLachlin C.J. explained that the test for showing causation is the "but for" test:

[8] 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 necessary to 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.

[9] 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. See Wilsher v. Essex Area Health Authority, [1988] A.C. 1074 (H.L.), at p. 1090, per Lord Bridge; Snell v. Farrell, 1990 CanLII 70 (SCC), [1990] 2 S.C.R. 311.

McLachlin C.J. stated that the material contribution test removes the requirements of "but for" causation and substitutes proof of material contribution to risk. Material contribution to risk, as opposed to injury, was the more accurate formulation of the test. McLachlin C.J. summarized the Supreme Court's jurisprudence on the material contribution approach:

[13] To recap, the basic rule of recovery for negligence is that the plaintiff must establish on a balance of probabilities that the defendant caused the plaintiff’s injury on the “but for” test. This is a factual determination. Exceptionally, however, courts have accepted that a plaintiff may be able to recover on the basis of “material contribution to risk of injury”, without showing factual “but for” causation. As will be discussed in more detail below, this can occur in cases where it is impossible to determine which of a number of negligent acts by multiple actors in fact caused the injury, but it is established that one or more of them did in fact cause it. In these cases, the goals of tort law and the underlying theory of corrective justice require that the defendant not be permitted to escape liability by pointing the finger at another wrongdoer. Courts have therefore held the defendant liable on the basis that he materially contributed to the risk of the injury.

[14] “But for” causation and liability on the basis of material contribution to risk are two different beasts. “But for” causation is a factual inquiry into what likely happened. The material contribution to risk test removes the requirement of “but for” causation and substitutes proof of material contribution to risk. As set out by Smith J.A. in MacDonald v. Goertz, 2009 BCCA 358, 275 B.C.A.C. 68, at para. 17:

. . . “material contribution” does not signify a test of causation at all; rather it is a policy-driven rule of law designed to permit plaintiffs to recover in such cases despite their failure to prove causation. In such cases, plaintiffs are permitted to “jump the evidentiary gap”: see “Lords a’leaping evidentiary gaps” (2002), Torts Law Journal 276, and “Cause-in-Fact and the Scope of Liability for Consequences” (2003), 119 L.Q.R. 388, both by Professor Jane Stapleton. That is because to deny liability “would offend basic notions of fairness and justice”: Hanke v. Resurfice Corp., para. 25.

[15] While the cases and scholars have sometimes spoken of “material contribution to the injury” instead of “material contribution to risk”, the latter is the more accurate formulation. As will become clearer when we discuss the cases, “material contribution” as a substitute for the usual requirement of “but for” causation only applies where it is impossible to say that a particular defendant’s negligent act in fact caused the injury. It imposes liability not because the evidence establishes that the defendant’s act caused the injury, but because the act contributed to the risk that injury would occur. Thus, this Court in Snell and Resurfice Corp. v. Hanke, 2007 SCC 7, [2007] 1 S.C.R. 333, raised the possibility of a material contribution to risk approach. The English law takes the same approach, as discussed below.

[16] Elimination of proof of causation as an element of negligence is a “radical step that goes against the fundamental principle stated by Diplock, L.J., in Browning v. War Office, [1962] 3 All E.R. 1089 (C.A.), at 1094-95: ‘. . . A defendant in an action in negligence is not a wrongdoer at large: he is a wrongdoer only in respect of the damage which he actually causes to the plaintiff’”: Mooney v. British Columbia (Attorney General), 2004 BCCA 402, 202 B.C.A.C. 74, at para. 157, per Smith J.A., concurring in the result. For that reason, recourse to a material contribution to risk approach is necessarily rare, and justified only where it is required by fairness and conforms to the principles that ground recovery in tort.

[....]

[28] To recap, the Canadian Supreme Court jurisprudence on a material contribution approach to date may be summarized as follows. First, while accepting that it might be appropriate in “special circumstances”, the Court has never in fact applied a material contribution to risk test. Cook was analyzed on a reverse onus basis. Snell, Athey, Walker Estate and Resurfice were all resolved on a robust and common sense application of the “but for” test of causation. Nevertheless, the Court has acknowledged the difficulties of proof that multi-tortfeasor cases may pose ― difficulties which in some cases may justify relaxing the requirement of “but for” causation and finding liability on a material contribution to risk approach.

McLachlin C.J. considered Resurfice where the Court had stated the material contribution test may be appropriate where it is "impossible" for the plaintiff to prove causation on the "but for" test and where it was clear that the defendant was negligent. McLachlin C.J. found that it was necessary to discuss what was meant by "impossible" and what negligence must be shown. McLachlin C.J. stated that the circumstances where it will be "impossible" for the "but for" test to be applied are demonstrated by the caselaw:

[39] What then are the cases referring to when they say that it must be “impossible” to prove “but for” causation as a precondition to a material contribution to risk approach? The answer emerges from the facts of the cases that have adopted such an approach. Typically, there are a number of tortfeasors. All are at fault, and one or more has in fact caused the plaintiff’s injury. The plaintiff would not have been injured “but for” their negligence, viewed globally. However, because each can point the finger at the other, it is impossible for the plaintiff to show on a balance of probabilities that any one of them in fact caused her injury. This is the impossibility of which Cook and the multiple-emp

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