This is an excerpt, with modifications, from Part 9 (“Some But-for Issues”) of “Black Holes, Aether“. Part 9 examines some of the problems in what Clements says about the but-for test and how that test is to be applied.
The only test the Clements acknowledges for proof of factual causation on the balance of probability is the but-for test.
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 fail.
The text of Clements suggests that the Supreme Court currently does not recognize any test for proof of factual causation on the balance of probability other than the but-for test. There is nothing in Clements that provides any basis for concluding that the Supreme Court would recognize any other test for proof of factual causation on the balance of probability.
Clements emphasizes the primacy of the Snell robust, pragmatic, “common sense” approach to the use of the but-for test. The Supreme Court wrote:
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.
The “but for” causation test must be applied in a robust common sense fashion.
Then, at the end of its review of the law, the Court summarized what Canadian lawyers are now to understand is the meaning of but-for doctrine and how the but-for test is to be applied.
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.
It may be that Clements will be understood, in due course, to have declared that the only method by which factual causation may be established, on the balance of probability, in Canadian negligence law is through the use of the but-for test.
In the course of reaching that summary, the Court wrote:
- 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.
- A common sense inference of “but for” causation from proof of negligence usually flows without difficulty. Evidence connecting the breach of duty to the injury suffered may permit the judge, depending on the circumstances, to infer that the defendant’s negligence probably caused the loss.
- Where “but for” causation is established by inference only, it is open to the defendant to argue or call evidence that the accident would have happened without the defendant’s negligence, i.e. that the negligence was not a necessary cause of the injury, which was, in any event, inevitable.
- In some cases, an injury — the loss for which the plaintiff claims compensation — may flow from a number of different negligent acts committed by different actors, each of which is a necessary or “but for” cause of the injury.
- “But for” causation is a factual inquiry into what likely happened.
- 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.
As should be evident from the above, taking the Court at its word, Clements leaves no room for any other test for factual causation in negligence, beyond those exceptions already established by the Supreme Court. Clements does not mention any other test. If the gravamen of factual causation in negligence is necessity, there cannot be any test which is something other than some version of a but-for test.
Once upon a time, not so long ago, science accepted the existence of something called the “aether”. Aether was understood to be an invisible, seemingly undetectable, substance permeating all of space that explained and justified many physical aspects of our world that the science of the time was not able to explain adequately; indeed, could not be adequately explained without assuming the existence of the aether, whatever it was. That belief was abandoned when experiments proved the accuracy of Albert Einstein’s Theory of General Relativity. While it is true that physicists and astronomers have now found that there is an invisible, detectable, something that permeates parts of space – called “dark matter” – and an invisible and so far undetectable something that permeates all of space – called “dark energy”, the necessity and existence of both substances has been established, to the satisfaction of most physicists, mathematically and by astronomical observation.
There is, currently, no saving equivalent for law’s concept of common sense. Common sense is causation jurisprudence’s aether. There is no evidence, in the cases, that a unique concept exists in causation jurisprudence which may be identified as common sense and nothing else. Common sense, if it has any meaning all, is nothing more than an alternative label for some of aspect of the process more formally known as logic. That remains true whether what is involved is deductive, inductive, or abductive logic, or any combination of those forms, and no matter the factors that law declares the judge or jury may be consider in deciding if the required causal relationship exists. … To say that a decision is a commonsense decision is to assert that it is logically consistent with the evidence upon which the decision is based. If a judge describes a decision as a commonsense conclusion, that judge will not describe the conclusion as illogical. But, the claim provides no meaningful explanation. I quote this succinct summary by Russell Brown:
A bald reference to “common sense” leaves judicial reasoning unexaminable, prone to judicially sanctioned “causal fictions”, and as such it is a “fertile breeding ground for miscarriages of justice.” It leaves little practical distinction between the judicial fact-finder’s reasoned factual determinations and the citizen fact-finder’s reasonless factual determinations.
Common sense, as it is currently used, is an empty description of a conclusion considered to be true because it is believed that the conclusion is the result of the valid application of the methodologies of inference drawing.
There is another useful analogy to science, so long as law claims to be a science and even if it should abandon that claim. common sense is also factual causation jurisprudence’s equivalent of the astronomical objects called “black holes”: stellar objects whose gravitational field traps anything – matter or radiation – that gets too close to the black hole. Like the black holes of our physical universe, not only can we not see inside of the black hole of common sense but nothing that falls into the clutches of common sense black hole escapes. However, unlike the stellar black hole, the black hole of common sense is completely black. It is not without irony, to the extent that this analogy to law’s common sense is meaningful, that the more energy a black hole consumes, the bigger it becomes, and that a black hole contains the most entropy of any object of an equivalent size, bearing in mind that entropy, in a scientific sense, is the absence of order. Why the irony? Because information is a manifestation of order. Whatever else it is, “Law” is an attempt to increase order: to reduce or at least limit disorder. In that sense, law is an attempt to defeat entropy. It is an attempt to defeat one of the basic physical laws of our reality. It turns out that, when used to describe what we know about a system, entropy is a measure of what we do not know. The greater the entropy in a system, the more we do not know about the basic constituents of that system so that we can better distinguish it from something which it is not.
A decision based upon unexplained common sense “is not even good enough to be wrong”. Rejecting the idea that unexplained common sense somehow reveals truth does not require lawyers and judges to “adventure … with philosophers.” It requires only that we pay attention to reality. The Supreme Court of Canada’s seeming insistence, highlighted in Clements, that the meaning of factual causation is captured by the but-for test is wrong. Borrowing a phrase an Ontario Court of Appeal decision, where the phrase was used in a different context – to describe a decision of a judge lower in the Ontario judicial pecking order – the belief “fails the reality test”. There are instances of factual causation which cannot be identified by the but-for test. These instances cannot be identified by the but-for test because the causal relationship between cause and consequence is not based on necessity. There are instances of factual causation where there is sufficient evidence to identify what amounts to multiple but-for causal relationships, in the sense that each of the identified causal relationships would be a but-for relationship if none of the other identified causal relationships existed. A but-for causal relationship is, by definition, a sufficient causal relationship. What these instances of seemingly multiple but-for causal relationships have is multiple sufficient causes to which, by definition, the but-for test as defined by Canadian law cannot be validly applied. Law should not adopt principles that fail the reality test.
 See ibid. at paras. 8-16.
 I will not use quotation marks around “common sense” again unless the phrase is quoted, or a label or part of title, or used as a placeholder for the construction “the term common sense”, or correct grammar otherwise requires quotation marks. The adjectival form should be “commonsense” not “common sense” in order for the phrase “common sense” to modify “approach – to describe an approach to the use of the but-for test. By rules of English grammar, “common” in the phrase “common sense approach” modifies “sense”. “Common sense” does not mean some form of human sense that is common to all people, or even a defined segment of humanity. However, “common sense approach” is the form of the phrase used in the case law (including Clements, at para. 23) ever since Snell.
 Clements, supra note 1 at paras. 8-9 [emphasis in original].
 Ibid., para. 46(1).
 Ibid. at para. 9.
 Ibid. at para. 10.
 Ibid. at para. 11.
 Ibid. at para. 12.
 Ibid. at para. 14. “Likely” must be understood to mean “probably”; that is, “more likely than not”.
 Ibid. at para. 13.
 See Part 4.C. of “Black Holes, Aether” dealing with the Walker Estate sufficient-condition material contribution to injury test which is limited to personal injury actions arising out of the negligent screening of blood donors. See Part 6, above, dealing with the apparent demise of the Athey material contribution to injury test as an alternative method for establishing factual causation on the balance of probability. Recall that the Court seems to have claimed that what was understood by lawyers, judges below the Supreme Court of Canada, and most academic lawyers, as the alternative Athey material contribution to injury test should never have been understood as a test for factual causation. Rather, the Athey reference to an alternative test should always have been understood as a material contribution to injury test which is not a test for proof of factual causation on the balance of probability. See Clements, supra note 9 at paras. 14-15.
 In physics, ”aether” was understood to be a ”[h]ypothetical substance filling space that provides the medium for light to propogate”. Brian Green, The Fabric of the Cosmos (New York: Vintage Books, 2004) at 537 (paperback) [Greene, Fabric of the Cosmos].
 Ibid. at 43-50.
 Ibid. at 294-303, 432-35, 524 n. 24.
 All conclusions are based on inferences, whether deductive, inductive, or abductive. See “Black Holes, Aether” note 634 for a list of articles discussing the process of judicial decision making based on inferences.
 Russell Brown and David Cheifetz, “The Bounds Of ‘Common Sense’ Inferences Of Causation: Clements v. Clements and the Art of Motorcycle Factum Maintenance” (2012) 40 Adv. Q. 34 at 60 [footnotes omitted]. … Ian Binnie, while still a judge of the Supreme Court of Canada, effectively described conclusions of this type, by jurors, as “wah wah”. See The Honourable Mr. Justice Ian Binnie, “Science in the Courtroom: The Mouse that Roared” (2007) 56 U.N.B.L.J. 307 at 315 [Binnie, “Science in the Courtroom]. The reference in the article is to an American juror’s post-trial explanation of the jury’s view of the evidence of the defendant’s experts. However, my reading of the context of passage in which Binnie explains that incident is that Binnie might have intended the “wah wah” to apply to the juror’s comment, too. Even if he did not, I do. The first sentence of the paragraph containing the juror’s statement is: “In some cases, it is clear that the scientific issues have not been properly understood.” The quotation is introduced this way: “Not only was Merck’s evidence not accepted, but the following was reported from a post-trial press conference held by the jurors”.
 Recent articles by Russell Brown provide an extremely useful explanation of the manner in which conclusions are made based on inferences: in Russell Brown, “Known Unknowns in Cause-in-Fact” (2011) 39 Adv. Q. 37 [Brown, “Known Unknowns”]; Russell Brown, “The Possibility of ‘Inference Causation’: Inferring Cause-In-Fact And The Nature Of Legal Fact-Finding” (2010) 55 McGill L. J. 1 [Brown, “Inference Causation”]; and Russell Brown, “Inferring Cause-in-Fact and the Search for Legal ‘Truth’”, in Richard Goldberg, ed., Perspectives on Causation (Oxford: Hart Publishing, 2011) 93 [Brown, “Legal Truth”]. This failure to explain what is meant by calls to common sense is not just a Canadian problem: see “Black Holes” at the text accompanying notes 569-572. It is also not just a Commonwealth problem: see M. MacCrimmon, “What is ‘Common’ about ‘Common Sense?: Cautionary Tales for Travelers Crossing Disciplinary Boundaries” (2001) 22 Cardozo L. Rev. 1433 at 1435: ‘Although frequently relied upon, common sense is seldom defined, nor is reliance on common sense justified.’
 Greene, Fabric of the Cosmos, supra note 13 at 537-38. Matter (thus energy) gets too close when it crosses the black hole’s event horizon. The event horizon is an ”[i]maginary sphere surrounding a black hole delineating the points of no return; anything crossing the event horizon cannot escape the black hole’s gravity”: ibid. at 538.
 When first discovered, physicists concluded that, because nothing – no matter, no energy – could escape the gravitational pull of collapsed stars colloquially called “black holes”, once the matter or energy crossed the black hole’s event horizon (the black hole’s boundary), then we could have no way of making any observations as to what is inside that horizon. That is, we have no way of testing, except mathematically, the validity of any of our conclusions as to the contents of a black hole, because nothing, once inside the event horizon, can get out. Stephen Hawking subsequently showed, mathematically, that black holes do emit some radiation from their surface (the event horizon) and subsequent astronomical observations have confirmed that conclusion. See Brian Greene, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos (New York: Vintage Books, 2011) at 274-75, 285-86 (paperback) [Greene, Hidden Reality]. See also supra note 19. Don’t let the title of the book mislead. It is an explanation, written at the general science level, of some of the implications of the discoveries in classical physics and quantum mechanics over the past century plus.
 It turns out that black holes radiate some energy as they have a miniscule nonzero temperature. Greene’s pithy summary, ibid. at 285, of Stephen Hawking’s discovery is that “black holes are thus not completely black”. The physical laws governing black hole creation mean that the temperature of a black hole is inversely proportional to the black hole’s mass – the more massive the black hole is, the lower its temperature is: ibid. at 285-86. The analogy to common sense would be: the greater the claim to common sense, the blacker – the more impenetrable – the claim becomes.
 Ibid. at 37-38, 286, 287-88, 296-98. “Law” is a system of rules. Entropy is “a measure of the disorder of a system”. “For an isolated system, the natural course of events takes the system to a more disordered (higher entropy) state.” “In any cyclic process the entropy will either increase or remain the same.” See online: <http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html> [accessed September 5, 2012]. Entropy is a consequence of one of the basic physical laws of our universe: the Second Law of Thermodynamics. In this context “cyclical” means not-static, or reversible. Another explanation of how entropy manifests in a natural process is: ”A natural process that starts in one equilibrium state and ends in another will go in the direction that causes the entropy of the system plus the environment to increase for an irreversible process and to remain constant for a reversible process”. See online: <http://www.grc.nasa.gov/WWW/k-12/airplane/thermo2.html> [accessed Sept. 5, 2012]. For present purposes, I am assuming that it is valid to describe law as a process that is subject to some principle analogous to entropy, even if ”Law” is not a ”natural” process in the sense used in science so is not formally subject to the Second Law of Thermodynamics.
 Decisions such as Clements and Resurfice show that judges are not always successful; not just because the connections between a legal system’s principles or rules sometimes means that increasing order in one part of the system increases the disorder in another to an extent that the overall effect is to increase disorder.
 Greene, Hidden Reality, supra note 376, at 287-289. A system’s entropy is “the minimum number of yes-no questions whose answers uniquely specify the microscopic details of the system”: ibid. at 410 n. 6. See also Greene, Fabric of the Cosmos, supra note 594 at 538: ”Entropy is “[a] measure of the disorder of a physical system; the number of rearrangements of a system’s fundamental constituents that leave its gross, overall appearance unchanged.”
 Paraphrase and translation of the physicist Wolfgang Pauli’s description of the merits of a scientific paper when asked if the paper was wrong: “This is not only not right, it’s not even wrong!”. [“Das ist nicht nur nicht richtig, es ist nicht einmal falsch!”] Quoted on Wikipedia.org <http://en.wikipedia.org/wiki/Wolfgang_Pauli> [accessed Sept. 22, 2012.]
 Frederick Pollock, The Law of Torts (Philadelphia, The Blackstone Publishing Co., 1887) at 25: “The lawyer cannot afford to adventure himself with philosophers in the logical and metaphysical controversies that beset the idea of cause.”
 See Authorson v. Canada (Attorney General) (2007), 86 O.R. (3d) 321 at para. 163, 2007 ONCA 501.