Readers of this blog who feel compelled to recite hosannas about the state of the Supreme Court of Canada’s jurisprudence dealing with causation in negligence – both factual causation and normative causation (i.e., legal causation without factual causation: think “material contribution”) and the need to separate the issue of causation from the issue of compensable damage – would do well to read, and consider, a very recent article by one of the deans of the subject in the Commonwealth: Jane Stapleton, “Unnecessary Causes”, 2013 128 Law Quarterly Review 39. The article is succinct enough (26 pages). It has subheadings, too. While the piece is notionally about United Kingdom law, it is generally applicable to common law Canada and has a section on Clements. The article is available online if one has access to Westlaw.

Clements apologists will take some comfort in some of what Professor Stapleton has to say about Clements. However, they should also pay heed to the point made in the first paragraph about the radical nature the Clements version of material contribution.

     The Canadian “material contribution to risk” rule is more radical than anything promoted in this article, for it assists the claimant over an evidentiary gap in relation to proving whether the defendant made any contribution to the mechanism by which injury occurred: it would, for example, permit the imposition of liability on all tortfeasors even where it was positively known that one made no contribution to the mechanism of injury at all, as in Cook v Lewis. In contrast, this article has only discussed situations where we know not only the basic mechanism by which an … injury occurred but that the breach in issue did in fact make a contribution to the relevant threshold step in the mechanism. But Chief Justice McLachlin’s rationale for the special rule and its limit to multiple wrongdoer cases is of importance here because it runs parallel to the normative concern that would, I have argued, lead the law to select benchmark (ii) as the appropriate one by which to judge if an … [overdetermined] …. injury represented “damage” to the claimant. Chief Justice McLachlin argued that Canada’s “material contribution to the risk” rule was justified in the relevant multiple wrongdoer cases because fairness and other “goals of tort law … require that the defendant not be permitted to escape liability by pointing the finger at another wrongdoer” where it is known that “the plaintiff would not have been injured ‘but for’ [the negligence of the other tortfeasors] viewed globally”.

As I have argued, where multiple tortfeasors are known to have each contributed to an oversubscribed threshold there is an equivalent objection to allowing one tortfeasor to argue that the injury to which he contributed nevertheless did not represent damage by pointing to other tortious contributions whose presence meant that the threshold would have been met anyway. In such contexts I have argued that an injury should be regarded as “damage” if but for all the tortfeasors’ contributions to the occurrence of the injury, that is but for all tortious contributions “viewed globally”, it would not have happened.

At 63 (internal footnote omitted). Canadian readers should note that Ms. Stapleton uses “indivisible” to mean instances of causation described as overdetermined in the literature.  Ms. Stapleton defines “indivisible injury cases” occur

where the relevant step in the mechanism by which the injury is known to occur requires a certain amount of an element, but does not require more and is not affected if there is more: I will call this phenomenon a “threshold” step. In an individual case such a threshold might have been “over-subscribed”, that is there may have been more of that element than was required to reach the threshold. This raises the possibility that, though the defendant’s breach made a positive contribution to the total of the element actually present, that contribution was unnecessary for the threshold point to be reached. In other words, where the relevant step in the mechanism involves a threshold it is possible that, absent the contribution resulting from the breach, the threshold would have been reached by the other contributions anyway: the breach would, in this sense, have contributed to the mechanism but been unnecessary for its completion.

At 40-41 (internal footnotes omitted). I’ve substituted “overdetermined” because of the special meaning, in the but-for context, that Canadian common law jurisprudence has given to “indivisible”.

Amongst the other points made by Ms. Stapleton is the reminder that the but-for test necessarily misses instances where there is overdetermined factual causation because each of the factual causes are not necessary. Exceptional tests for causation such as the “material contribution” test do not apply because it is the case that each of the factual causes was involved. It is not a case where the evidence produces the one or more, but not all, of the multiple tortfeasors, but one cannot say which of them. Thus:

A, B and C, acting independently but simultaneously, each negligently lean on Paul’s car, which is parked at a lookout at the top of a mountain. Their combined force results in the car rolling over a diminutive curbstone and plummeting down the mountain to its destruction. The force exerted by the push of any one actor would have been insufficient to propel Paul’s car past the curbstone, but the combined force of any two of them is sufficient.[fn 20]

No individual was necessary for the destruction of the car, yet it seems plausible that the law would want to identify their role. If the law required a factor to satisfy the but-for test before it would be recognised as a factual “cause”, the striking result would be that, while it would be known exactly what happened and by what agency, the law would not identify any of these three individuals as a “cause” of the car’s destruction.

     It is true that a legal system might choose this course. It might then leave the court in an individual case to decide whether the individual “should be taken to” be a “factual cause” on the basis of a normative judgment about “whether and why responsibility for the harm should be imposed on the tortfeasor”. But this obfuscates the analysis because it conflates the fact that A pushed the car with the separate issue of whether A ought to be held legally responsible for its destruction. Legal analysis would not be reflecting physical reality if A’s indisputable physical role in the occurrence is only to be acknowledged if the court determines that A should be responsible for the harm. A more transparent and therefore preferable approach is for the law to designate the relation each pusher has to the destruction of the car as a factual “cause”. Each can then be subjected to the separate normative investigation concerning legal responsibility.

I set out her conclusion at 64-65.

1.    In most cases it is clear from our knowledge of the general way the injury came about that the breach would have been either necessary for the occurrence of the injury, or it would not have been involved in any way at all. It is this knowledge about the relevant mechanism in play that justifies the simplified approach to factual causation represented by the but-for test.

2.    Where, however, we know that the mechanism by which an indivisible injury occurs involves a threshold concentration of some element (that is, it requires a certain concentration of the element but does not require more and is not relevantly affected if there is more), the but-for test should not be used as the test of factual causation. This is because it prevents the law identifying a relation that may be of normative interest, namely the relation between the occurrence of the injury and an actual contribution of some of that element which contribution, however, had not been necessary for the threshold to have been reached.

3.    It should, therefore, be a general principle of private law that a breach will be recognised as a “factual cause” of the occurrence of an injury whenever:

• either, but for the breach, the injury would have been prevented [fn 121] ;
• or, the breach resulted in some positive contribution (even if unnecessary) to the relevant threshold step in the mechanism by which the indivisible injury came about.

4.    The “no better off” principle requiring that compensatory tort damages do not make a claimant better off than he would have been had he not been the victim of tortious conduct, can be expressed as the requirement that the injury represent “damage” relative to the benchmark of where the victim would have been absent tortious conduct.

5.    As a matter of legal analysis tort law should distinguish: whether the breach made a causal contribution to the occurrence of the indivisible injury of which complaint is made (the “factual causation” issue); from whether that injury represents “damage”. Forensically these questions should be dealt with separately since the evidence relevant to each may be different, as in oversubscribed threshold cases.

6.    The phenomenon of unnecessary causes of an indivisible injury reveals that tort law has a choice of benchmarks in assessing the “damage” issue: (i) where the victim would have been but for the tortious conduct of the individual defendant; or (ii) where the victim would have been but for all tortious contributions to the occurrence of the injury. Benchmark (ii) is normatively superior.

____________

20.  Restatement (Third) of Torts: Liability for Physical and Emotional Harm (St Paul, MN: American Law Institute Publishers, 2010), § 27, illust.3.

…

121. Either because the breach made a positive and necessary contribution to the mechanism by which injury occurred (e.g. the straw that broke the camel’s back) or because the breach resulted in the absence of part of a prevention mechanism which would have operated had that part been present (e.g. a failure to secure dangerous Borstal trainees) …