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Evidence - Expert Opinion - Necessity (Mohan). International Air Transport Association v. Canada (Transportation Agency)
In International Air Transport Association v. Canada (Transportation Agency) (SCC, 2024) the Supreme Court of Canada dismissed an appeal, here involving "the vires of the Air Passenger Protection Regulations, SOR/2019-150 (“Regulations”) [SS: under the 'Canada Transportation Act'], and the nature and scope of the “exclusivity principle” set out in Article 29 of the 1999 Convention for the Unification of Certain Rules for International Carriage by Air" [SS: the 'Montreal Convention'].
Here the court engages in a useful consideration of expert evidence doctrine (Mohan/necessity), and foreign and international law (as the object of the evidence inquiry):[68] Justice de Montigny noted that the case law has not been consistent in its treatment of expert evidence regarding international law. Some appellate courts have taken judicial notice of international law (see Turp v. Canada (Foreign Affairs), 2018 FCA 133, [2019] 1 F.C.R. 198) or have otherwise considered questions of customary and conventional international law without recourse to expert evidence (e.g., Suresh v. Canada (Minister of Citizenship and Immigration), 2002 SCC 1, [2002] 1 S.C.R. 3 (considering peremptory norms of international law); Yugraneft Corp., at paras. 19 and 21 (considering the Convention on the Recognition and Enforcement of Foreign Arbitral Awards, Can. T.S. 1986 No. 43)). However, on at least two occasions, courts have admitted expert evidence on questions of international law (Holding Tusculum B.V. v. S.A. Louis Dreyfus & Cie, 2006 QCCS 2827, at para. 16 (CanLII); Fédération des travailleurs du Québec (FTQ - Construction) v. Procureure générale du Québec, 2018 QCCS 4548, at para. 20 (CanLII)).
[69] The appellants, the Attorney General and the Federal Court of Appeal have sought clarification on this issue. I agree that such clarification is timely.
(1) Mohan Governs Expert Evidence on Questions of International Law
[70] The appellants and the Attorney General are, for the most part, ad idem that the Mohan framework be used to determine the admissibility of the expert evidence. The appellants submit that “[e]xpert evidence is necessary when it is likely to provide information outside the judge’s experience and knowledge” (A.F., at para. 107). The appellants submit that it may be “necessary for a court to receive expert evidence where the normative content of international law is unsettled, controversial or emerging” (para. 111). They further argue that Canadian judges may find it difficult to ascertain the content of international law because it implicates practice in foreign states, making expert evidence important in this context. The Attorney General agrees that Mohan governs, but argues that expert evidence on a legal issue before the court is inadmissible as such expert evidence would usurp the court’s role. Justice de Montigny, in weighing these arguments, noted that whether “international law [should] be treated as a question of fact” is “a vexed question” (C.A. reasons, at para. 46).
[71] While some courts of first instance deal infrequently with international law, others do so with more regularity. For example, the Federal Court often encounters international legal issues due to the nature of its jurisdiction. The approach of some courts of first instance to expert evidence has been described as “inconsistent, and often under-reasoned” (G. van Ert, Recent Federal Courts decisions on expert evidence of international law, December 31, 2018 (online); see also G. van Ert, “The Admissibility of International Legal Evidence” (2005), 84 Can. Bar Rev. 31). As a result, clarification of how to determine the admissibility of expert evidence, when such is necessary, may be beneficial.
[72] The test from Mohan should be applied in the context of international law as it is in other circumstances where expert evidence is sought to be admitted. Under the Mohan test, expert evidence is admissible when it is “necessary in the sense that it provides information ‘which is likely to be outside the experience and knowledge of a judge . . .’” (p. 23, quoting R. v. Abbey, 1982 CanLII 25 (SCC), [1982] 2 S.C.R. 24). The test is as follows: At the first stage, judges must consider the threshold requirements of admissibility set out in Mohan. There are four threshold requirements: “. . . (1) relevance; (2) necessity in assisting the trier of fact; (3) absence of an exclusionary rule; and (4) a properly qualified expert . . .” (White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, [2015] 2 S.C.R. 182, at para. 19, citing Mohan, at pp. 20-25). At the second stage — the discretionary “gatekeeping” stage — judges must balance the potential risks and benefits of admitting the evidence and determine whether the benefits outweigh the risks. Mohan’s “basic structure for the law relating to the admissibility of expert opinion evidence” is applicable in a wide range of contexts outside the experience of judges (White Burgess, at para. 19). See, for example, Masterpiece Inc. v. Alavida Lifestyles Inc., 2011 SCC 27, [2011] 2 S.C.R. 387, at para. 75 (intellectual property); Clayson-Martin v. Martin, 2015 ONCA 596, 127 O.R. (3d) 1 (medical reports); and R. v. Abdullahi, 2021 ONCA 82, 399 C.C.C. (3d) 397, at para. 34 (linguistics and translation).
[73] As with areas of the law such as those noted above, from time to time difficult and contentious questions of international law will arise where judges will be assisted in carrying out their functions by appropriate expert evidence. Questions of conventional international law may require judges to have regard to questions of fact that are susceptible to expert evidence including, inter alia, foreign law (in applying a treaty, for example), state practice in a treaty’s application, or the authentic text of a treaty in a foreign language (see G. van Ert, Using International Law in Canadian Courts (2nd ed. 2008), at pp. 57 and 63). Similarly, in the context of customary international law, “alleged customs may be contested and require proof” (p. 67). Mohan is sufficiently flexible to enable courts to admit expert evidence on such questions, where it is needed for a court to carry out its functions.
[74] To summarize, then, the appropriate framework is the following. Where expert evidence satisfies Mohan’s criteria, it may be considered. Otherwise, judges should proceed as they would for any other question of law — that is, on the basis of the submissions of the parties before the court and authorities on which they rely.
[75] This Court on various occasions has considered the meaning of treaties without recourse to expert evidence, including in Thibodeau and Yugraneft Corp. Looking to the principles of treaty interpretation codified in the Vienna Convention, and undertaking an examination of the text, object, and purpose of a treaty, is within the capacity of Canadian courts.
[76] In Suresh, this Court considered the peremptory norm of international law regarding the prohibition of torture; this required the Court to have regard to international conventions which Canada has ratified and to jus cogens norms of international law. The Court had recourse to academic texts, foreign jurisprudence, as well as the submissions of parties and interveners. These sources sufficed for the Court to consider the status of the prohibition against torture as a matter of international law.
[77] Though the Court did not rely on Mohan in these cases, its approach to dealing with questions of international law without recourse to expert evidence is consistent with Mohan’s suggestion that “[i]f on the proven facts a judge or jury can form their own conclusions without help, then the opinion of an expert is unnecessary” (p. 24).
[78] Finally, I note that evidence law jurisprudence establishes a number of cautionary rules that apply with equal force in the context of expert evidence sought to be admitted regarding international law. First, as noted in Quebec (Attorney General) v. Canada, 2008 FC 713, 359 F.T.R. 1, aff’d 2009 FCA 361, 400 N.R. 323, aff’d 2011 SCC 11, [2011] 1 S.C.R. 368, the role of an expert is “only to assist the court in assessing complex and technical facts. It must never be forgotten that, ultimately, it is the court that must decide questions of law” (para. 161). Furthermore, “[e]xpert opinions will be rendered inadmissible when they are nothing more than the reworking of the argument of counsel participating in the case” (Surrey Credit Union v. Willson (1990), 1990 CanLII 1983 (BC SC), 45 B.C.L.R. (2d) 310 (S.C.), at p. 315).
[79] In applying Mohan, the admissibility of expert evidence is within the court’s discretion so long as the threshold requirements of admissibility are satisfied. Given the variety of contexts in which expert evidence is sought to be adduced on questions of international law, the admissibility of such evidence is best left as a matter of judicial discretion rather than being subject to a fixed and invariable rule. . Meady v. Greyhound Canada Transportation Corp.
In the tort case of Meady v. Greyhound Canada Transportation Corp. (Ont CA, 2015) the Court of Appeal considered 'necessity' of the evidence as it forms an element of the leading Mohan case criteria for admissibility of expert opinion evidence:Principles Governing the Admissibility of Expert Evidence
[31] In considering the admissibility of the expert evidence, the trial judge correctly identified the test in R. v. Mohan, 1994 CanLII 80 (SCC), [1994] 2 S.C.R. 9, as explained by this court in R. v. Abbey, 2009 ONCA 624 (CanLII), 97 O.R. (3d) 330, leave to appeal to S.C.C. refused, [2010] S.C.C.A. No. 125. The test has four requirements: (a) the evidence must be relevant; (b) it must be necessary to assist the trier of fact; (c) it must not be subject to an exclusionary rule; and (d) the expert must be properly qualified.
[32] The issue on this appeal is the second requirement – the necessity of the evidence to assist the trier of fact. In Mohan, at p. 23, the Supreme Court explained that necessary evidence must be outside the knowledge and experience of the trier of fact:This pre-condition is often expressed in terms as to whether the evidence would be helpful to the trier of fact. The word "helpful" is not quite appropriate and sets too low a standard. However, I would not judge necessity by too strict a standard. What is required is that the opinion be necessary in the sense that it provide information "which is likely to be outside the experience and knowledge of a judge or jury": as quoted by Dickson J. in R. v. Abbey,1982 CanLII 25 (SCC), [1982] 2 S.C.R. 24]. As stated by Dickson J., the evidence must be necessary to enable the trier of fact to appreciate the matters in issue due to their technical nature. In Kelliher (Village of) v. Smith, 1931 CanLII 1 (SCC), [1931] S.C.R. 672, at p. 684, this Court, quoting from Beven on Negligence (4th ed. 1928), at p. 141, stated that in order for expert evidence to be admissible, "[t]he subject-matter of the inquiry must be such that ordinary people are unlikely to form a correct judgment about it, if unassisted by persons with special knowledge". [33] The application of the necessity criterion asks whether the trier is able to form a correct judgment about the issue without the assistance of persons with special knowledge.
[34] The general standard of care of a professional, such as a police officer, is a question of law, but the content of the standard of care in a particular case is a question of fact. As such, the content of the standard will generally require expert evidence: Krawchuk v. Scherbak, 2011 ONCA 352 (CanLII), 106 O.R. (3d) 598, at para. 125, 133, leave to appeal to S.C.C. refused, [2011] S.C.C.A. No. 319.
[35] This is, however, subject to the exception for “nontechnical matters or those of which an ordinary person may be expected to have knowledge”: Krawchuk, at para. 133, referring to Zink v. Adrian (2005), 2005 BCCA 93 (CanLII), 37 B.C.L.R. (4th) 389, at para. 44.
[36] The trial judge invoked this exception in refusing to admit the expert evidence. He quoted the British Columbia Court of Appeal in Burbank, above, at para. 79:Expert evidence would only be necessary (and therefore admissible) to establish the standard of care in a negligence case of this kind if the conduct in question gave rise to considerations beyond common understanding. Evidence that need not invariably be expert evidence might be adduced to prove the training police officers are given, or to explain police practice, or where needed to interpret and explain the application of requirements contained in legislation or policy with which the trier of fact is unlikely to be familiar. These are just examples of the kind of evidence that where needed might go toward assisting the court in establishing the standard of care. But unless the nature of the inquiry into the conduct of a police officer is actually beyond the common understanding or experience of judge or jury, evidence of the standard of care, particularly expert opinion, is not required and should not be admitted. It is not otherwise necessary to adduce evidence that a police officer failed to meet the standard of care of a competent police officer. [37] There has been growing recognition of the responsibility of the trial judge to exercise a more robust gatekeeper role in the admission of expert evidence – see: Lisa Dufraimont, “New Challenges for the Gatekeeper: The Evolving Law on Expert Evidence in Criminal Cases” (2012) 58 C.L.Q. 531; and Report of the Inquiry into Pediatric Forensic Pathology in Ontario (Toronto: Queen’s Printer for Ontario, 2008), vol. 3, c. 18: “Role of the Court”. This observation holds true for both civil and criminal contexts. Although much of the discussion has focused on increasing scrutiny of threshold reliability at the gatekeeper stage, it is equally important to ensure the evidence is genuinely necessary.
[38] There are compelling rationales underlying this approach. Unnecessary expert evidence distracts the trier of fact from the issues at hand, complicates the proceeding, prolongs the trial and increases the cost of litigation. In Masterpiece Inc. v. Alavida Lifestyles Inc., 2011 SCC 27 (CanLII), [2011] 2 S.C.R. 387, Rothstein J. stated at para. 77:If a trial judge concludes that proposed expert evidence is unnecessary or irrelevant or will distract from the issues to be decided, he or she should disallow such evidence from being introduced. [39] In a similar vein, Moldaver J.A. (as he was then) stated in Johnson v. Milton (Town), 2008 ONCA 440 (CanLII), 91 O.R. (3d) 190, at para. 48:Trial judges should do their best to perform the gatekeeper function they have been assigned, if for no other reason than trial economy. Permitting experts to give evidence on matters that are commonplace or for which they have no special skill, knowledge or training wastes both time and resources and adds stress to an already overburdened justice system. It is also legally incorrect. [40] As Doherty J.A. observed in 2009 in Abbey, at paras. 93-95, in assessing whether the evidence is necessary to the proper adjudication of the facts, the trial judge conducts a cost-benefit analysis – whether the benefits of admission are sufficiently strong to outweigh the associated costs. This is part of the judge’s gatekeeper function and involves an exercise of discretion. It is an analysis that does not necessarily admit of a “yes” or “no” answer: Abbey, at para. 79.
[41] In one of his rulings, the trial judge referred to Bryant, Lederman and Fuerst, The Law of Evidence in Canada, 3rd ed. (Markham: LexisNexis, 2009) at pp. 799-800, where the authors observe that there is “no bright line” to determine whether the subject matter of expert evidence falls within the normal experience of a particular trier of fact. The authors quote the judgment of this court in R. v. D.S.F. (1999), 1999 CanLII 3704 (ON CA), 43 O.R. (3d) 609 (C.A.), in which O’Connor J.A. observed, at p. 625:There is no exact way to draw the line between what is within the normal experience of a judge or a jury and what is not. The normal experiences of different triers of fact may differ. Over time the subject matters that come within the normal experiences of judges and juries may change. The normal experiences of those in one community may differ from those in other communities. In the end, the court in each case will be required to exercise its best judgment in deciding whether a particular subject matter is or is not within the normal experience of the trier of fact. [42] For these reasons, deference is owed to the exercise of the trial judge’s gatekeeper function in excluding unnecessary evidence. The trial judge is best equipped to appreciate the issues in the context of the evidence as it unfolds and to determine the extent to which, if at all, expert evidence is required to assist the trier of fact in the disposition of the issues: R. v. D.D., 2000 SCC 43 (CanLII), [2000] 2 S.C.R. 275, at paras. 12-13.
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