In this, since it is in reference to what would have happened If the defendant’s negligent action would not have occurred it is in part a counterfactual claim based on dependency (Lewis, 1973, pp. 556-558). It is not a claim about what happened in actuality but more so what would have happened in a different scenario where the negligent action did not occur.

Although the “but for” test if passed, means that the negligence was necessary in a legal context, it also allows for this to be proven on a balance of probabilities ( Clements v. Clements, 2012 , para 8). In this, a plaintiff must show based on a robust common sense approach to the “but for” test that more likely than not, if this negligent action did not occur then this injury would not have occurred (Clements v. Clements, 2012 , para 23). With this in mind, scientific proof does not need to be established to prove causation in a legal context (Clements v. Clements, 2012 , para 38).

The “but for” test is the primary rule for recovery; however, in exceptional cases the “but for” test can be substituted by a material contribution to risk assessment when it is “impossible” for causation to be proven using the “but for” test ( Clements v. Clements, 2012 , para 27).

The material contribution to risk of injury assessment is a test that, “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.” ( Clements v. Clements, 2012 , para 15).

In this, if a material contribution test is permitted, a plaintiff does not need to prove causation or counterfactual dependency, but rather merely needs to prove that the defendant’s negligence contributed to the risk of the injury to succeed. 

However, in this the Court has noted that moving from a “but for” test to a material contribution assessment is not merely moving to a different analysis of counterfactual causation, but an elimination of causation entirely, at least in a counterfactual understanding (Clements v. Clements, 2012 , para 16).

As such, since forgoing causation in a case of negligence is a step that goes against the foundational conventions of negligence and as such should be used rarely and only when necessary (Clements v. Clements, 2012 , para 16).

 

There has been some disputes regarding if it is more prudent to interpret this as, “material contribution to injury” or, “material contribution to risk” as a substitution for “but for”, or if there is even a practical difference at all, as seen in Snell v. Farrell (1990).

In Clements, the driver of a motorcycle was riding with his wife who was a passenger. In this, they were riding in wet conditions and unbeknownst to the driver a nail had punctured the rear tire. However, the bike was also overloaded by 100 pounds and the driver went past the speed limit, driving 120km/h in a 100km/h zone when attempting to overtake a car. Subsequently the nail fell out of the tire, causing the rear tire to deflate, making the bike unstable, leading to a crash. This crash lead to the passenger suffering injuries and suing the driver on the basis that his negligence caused her injury (Clements v. Clements, 2012 , paras 1-3).

The trial judge found that the “but for” test was unable to prove causation due to limitations of scientific reconstruction. As such, a material contribution assessment was used instead and found the driver, Joseph Clements liable on this basis (Clements v. Clements, 2012 , para 3).

Concerning the courts’ analysis of this concept, this entry will mainly focus on considerations made by the Supreme Court of Canada in Clements, including different types of impossibility and its analysis of other cases in relation to impossibility and “but for”.

In Clements, ideas of impossibility considered included logical impossibility, scientific impossibility, and impossibility due to multiple tortfeasors (Clements v. Clements, 2012 , para s 34-39).

In Clements, the Court considered impossible to prove via logical impossibility or conceptual impossibility (Clements v. Clements, 2012 , para 36). This often refers to the notion that something is logically impossible if it either contains or entails a contradiction, or if it is inconceivable (Levy, 1971, pp. 166, 180, 184). However, that which is often “inconceivable” in this context is often merely that which is contradictory (Levy, 1971, p. 166).

However, the Court noted that implementing this as the understood definition of impossibility in this context could lead to unresolved confusion. In many cases where it appeared that causation could not be proved using “but for”, the difficulty was not based around whether proving a specific plaintiff’s negligence was contradictory but that there was factual difficulty connecting a specific negligent action to the injury (Clements v. Clements, 2012 , para 36).

For example, In  Cook v. Lewis,[1951] S.C.R. 830, proving which of the tortfeasors’ negligent action’s was responsible for the injury suffered by the plaintiff is not inconceivable, nor is it contradictory (Clements v. Clements, 2012 , para 36). Nevertheless, determining which of the defendants negligence was the one which caused the injury was highly implausible, due to the facts present at the time, the implausibility of gaining more relevant evidence, and since either one of the tortfeasors could “point the finger” at the other regarding responsibility (Clements v. Clements, 2012 , para 36).

Furthermore, if logical impossibility became the standard definition of impossibility, and subsequently the marker of whether the “but for” test should be replaced, then any case where finding proof is conceivable and not contradictory, “but for” would not be replaced. However , this definition of impossibility is irrelevant or insufficient in resolving the problems with the “but for” test in cases such as in Cook, as it merely posits that finding out which of the tortfeasors actions caused the injury is possible, or that either tortfeasors actions could have caused the injury, not which of the tortfeasors actions did cause the injury. With this in mind, implementing this notion of “impossibility” would result in issues for Cook and cases like it, as these cases have sufficient problems with proving causation using the “but for test”; however, under this definition they would not meet the standards of being a sufficient case of impossibility and as such a “but for” test would still be applied, resulting in no recovery. As such this poses problems by not resolving problems that ought to be resolved and by permitting cases where it was clear that some negligence caused the injury; however, no recovery would be granted due to unresolved problems with the “but for” test caused by “impossibility” being defined as logical impossibility.

As such, implementing notions of logical impossibility in this context is often irrelevant or insufficient to the difficulties in proving causation. With this in mind, the Court found that this should not be the definition of “impossibility” used when determining when the “but for” test should be replaced by a material contribution assessment (Clements v. Clements, 2012 , para 36).

Another form of impossibility that was considered was “scientific impossibility”, which in reference to the Courts interpretation in Clements was in regard to notions where based on the facts and current scientific developments, scientific proof regarding causation cannot be established (Clements v. Clements, 2012 , para 38).

However, the Courts re-stated that the law of negligence does not require scientific proof to determine causality via the “but for” test, where a robust common sense inference based on the facts can be sufficient (Clements v. Clements, 2012 , para 38, 49).

As such, since scientific proof is not required to determine causation using the “but for” test, it appears difficult to posit that causation regarding a particular case being impossible to prove scientifically entails that this causation cannot be evaluated by the “but for” test.

In Clements, the Court found that after considering various definitions of impossibility, the circumstances in which it appears permissible to consider it “impossible” to prove causation using the “but for” test are those which have multiple tortfeasors (Clements v. Clements, 2012 , para 39).

Furthermore, this is only “impossible” when the multiple tortfeasors committed negligent acts where it is clear that one or more of these caused injury to the plaintiff; however, based on the facts, one cannot show on a balance of probabilities that any particular one of the tortfeasors negligent actions was the one that caused that injury (Clements v. Clements, 2012 , para 39).

This is due to defendants being able to note that based on the facts their negligence is not more likely than not the cause of the injury than that of another defendant’s negligence (Clements v. Clements, 2012 , para 39-40, 45) . In this, if two tortfeasors committed negligent acts where one of them caused injury, but based in the evidence it provides no insight into which, it is hard to determine that one was 51% or more likely to have caused this injury than that of the other based on the facts, but rather at most each was 50% likely to have caused the injury (Acharya, 2014, p. 209) . As such, since determining causation on a balance of probabilities requires a claim to be more than 50% true, a plaintiff cannot prove on a balance of probabilities that either plaintiff’s negligence caused the injury and recovery is denied. However, in this it is still clear that some negligence occurred which caused the injury, which goes against the goals of negligence for the Court ( Clements v. Clements, 2012 , para 40-41, 43). 

As such, The Court determined that a material contribution assessment can replace the traditional “but for” test when “but for” proves causation globally, but can not prove causation regarding a particular negligent act ( Clements v. Clements, 2012 , para 46).

Consequently, in Clements, the Court concluded that a plaintiff cannot succeed when causation cannot be proven by the “but for” test at least globally ( Clements v. Clements, 2012 , para 46).

Now although interpreting logical impossibility in terms of contradiction and inconceivability much like that of the Court in Clements is correct, it is often more so an ontological claim. In this, it is a statement about what circumstances could exist; however, as previously analyzed, this leads to unresolved difficulties in proving causation. Beyond what is considered logically impossible being too large in scope, what is being analyzed isn’t necessarily what exists, but rather what we can know and prove. As such, since what is being analyzed is less so about conceivability and more so about justification, this is perhaps better fit as a standard of epistemology.

Furthermore, although this entry agrees that logical impossibility is insufficient to resolving problems surrounding “but for”, perhaps there is still room for other philosophical notions to be considered.

One of the areas this entry seeks to address regarding the conclusion in Clements (regarding impossibility) is that it appears less so based on an abstract rule, but more so based on a particular example. In this, although it is clear that it is impossible, and to an extent why, based on these findings, it is hard to clearly articulate in abstract terms what properties in particular made it “impossible” to justify causation.

With this in mind, this entry seeks to further investigate whether there can be further added clarity as to what conditions do contribute to “impossibility” and how, and what subtypes can contribute to “impossibility”.