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Proving factual causation: the process of drawing causal inferences

From Russell Brown,* “Cause-in-Fact at the Supreme Court of Canada: Developments in Tort Law in 2012-13” (2014), 64 S.C.L.R. (2d) 327 at 331

(* now a Justice of the Alberta Court of Appeal and Honorary Professor of Law at the University of Alberta; Justice of the Court of Queen’s Bench of Alberta at the time of publication)

       It is worth making two observations about the drawing of a causal inference.  First, there is nothing unorthodox about the proposition that a fact-finder may draw causal inferences, even in the absence of verifying scientific evidence.  Inference-drawing is inherent not only in all causal fact-finding, but in all fact finding.  Just as one might infer from evidence that an automobile made a screeching noise immediately prior to a collision that the driver saw the obstruction just before striking it, one may also infer (or not infer) that evidence of risk, of harm and of the surrounding circumstances is so arrayed so as to support the drawing of an inference of a causal relationship between the risk and the harm – and all without the reassurance of expert evidence.  And, just as the absence of direct evidence that the driver saw the obstruction before hitting it does not preclude an inference that he or she did, the absence of direct evidence verifying a causal link between risk and harm is similarly not determinative.  Fact-finders infer, or they do not infer, and they may do so on evidence that bears only indirectly to the proposition being advanced.[16]

The second observation is that causal inference-drawing is not presented in Snell as some form of alternative or watered-down version of the but for test.[17]  If all fact-finding is necessarily inferential, then fact-finding to the but for standard is also inferential.  So long as the inference is drawn on a balance of probabilities, causal inference is no alternative to the but for test, but is an instantiation of it.  It is how the but for test is to be applied – and not merely in some cases, but in all cases.

[Emphasis added.]

[16] Russell Brown, “The Possibility of ‘Inference Causation’:  Inferring Cause-in-Fact and the Nature of Legal Fact-Finding” (2010) 55 McGill L.J. 1, at 30-35 [Brown, “Inference Causation”].

[17] This was the criticism of Lewis Klar, in Tort Law, 3d ed. (Toronto:  Thomson Carswell, 2003) at 403:  “[w]hile [inference-drawing] may produce a pragmatic solution to a plaintiff’s dilemma in difficult causation cases, it does depart from the traditional “but for” test, and the balance of probability standard.”  This statement does not appear in subsequent editions of Professor Klar’s book.

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