SUPREME COURT OF CANADA

Date: 20150430 Docket: 35492 Between: White Burgess Langille Inman, carrying on business as WBLI Chartered Accountants and R. Brian Burgess Appellants and Abbott and Haliburton Company Limited, A.W. Allen & Son Limited, Berwick Building Supplies Limited, Bishop’s Falls Building Supplies Limited, Arthur Boudreau & Fils Ltée, Brennan Contractors & Supplies Ltd., F. J. Brideau & Fils Limitée, Cabot Building Supplies Company (1988) Limited, Robert Churchill Building Supplies Limited, CDL Holdings Limited, formerly Chester Dawe Limited, Fraser Supplies (1980) Ltd., R. D. Gillis Building Supplies Limited, Yvon Godin Ltd., Truro Wood Industries Limited/Home Care Properties Limited, Hann’s Hardware and Sporting Goods Limited, Harbour Breton Building Supplies Limited, Hillier’s Trades Limited, Hubcraft Building Supplies Limited, Lumbermart Limited, Maple Leaf Farm Supplies Limited, S.W. Mifflin Ltd., Nauss Brothers Limited, O’Leary Farmers’ Co-operative Ass’n. Ltd., Pellerin Building Supplies Inc., Pleasant Supplies Incorporated, J. I. Pritchett & Sons Limited, Centre Multi-Décor de Richibucto Ltée, U. J. Robichaud & Sons Woodworkers Limited, Quincaillerie Saint-Louis Ltée, R & J Swinamer’s Supplies Limited, 508686 N.B. INC. operating as T.N.T. Insulation and Building Supplies, Taylor Lumber and Building Supplies Limited, Two by Four Lumber Sales Ltd., Walbourne Enterprises Ltd., Western Bay Hardware Limited, White’s Construction Limited, D. J. Williams and Sons Limited and Woodland Building Supplies Limited Respondents

• and - Attorney General of Canada and Criminal Lawyers’ Association (Ontario) Interveners Coram: McLachlin C.J. and Abella, Rothstein, Cromwell, Moldaver, Wagner and Gascon JJ. Reasons for Judgment: (paras. 1 to 63) Cromwell J. (McLachlin C.J. and Abella, Rothstein, Moldaver, Wagner and Gascon JJ. concurring) White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, [2015] 2 S.C.R. 182 White Burgess Langille Inman, carrying on business as WBLI Chartered Accountants and R. Brian Burgess Appellants v. Abbott and Haliburton Company Limited, A.W. Allen & Son Limited, Berwick Building Supplies Limited, Bishop’s Falls Building Supplies Limited, Arthur Boudreau & Fils Ltée, Brennan Contractors & Supplies Ltd., F. J. Brideau & Fils Limitée, Cabot Building Supplies Company (1988) Limited, Robert Churchill Building Supplies Limited, CDL Holdings Limited, formerly Chester Dawe Limited, Fraser Supplies (1980) Ltd., R. D. Gillis Building Supplies Limited, Yvon Godin Ltd., Truro Wood Industries Limited/Home Care Properties Limited, Hann’s Hardware and Sporting Goods Limited, Harbour Breton Building Supplies Limited, Hillier’s Trades Limited, Hubcraft Building Supplies Limited, Lumbermart Limited, Maple Leaf Farm Supplies Limited, S.W. Mifflin Ltd., Nauss Brothers Limited, O’Leary Farmers’ Co-operative Ass’n. Ltd., Pellerin Building Supplies Inc., Pleasant Supplies Incorporated, J. I. Pritchett & Sons Limited, Centre Multi-Décor de Richibucto Ltée, U. J. Robichaud & Sons Woodworkers Limited, Quincaillerie Saint-Louis Ltée, R & J Swinamer’s Supplies Limited, 508686 N.B. INC. operating as T.N.T. Insulation and Building Supplies, Taylor Lumber and Building Supplies Limited, Two by Four Lumber Sales Ltd., Walbourne Enterprises Ltd., Western Bay Hardware Limited, White’s Construction Limited, D. J. Williams and Sons Limited and Woodland Building Supplies Limited Respondents and Attorney General of Canada and Criminal Lawyers’ Association (Ontario) Interveners Indexed as: White Burgess Langille Inman v. Abbott and Haliburton Co. 2015 SCC 23 File No.: 35492. 2014: October 7; 2015: April 30. Present: McLachlin C.J. and Abella, Rothstein, Cromwell, Moldaver, Wagner and Gascon JJ. on appeal from the court of appeal for nova scotia Evidence — Admissibility — Expert evidence — Basic standards for admissibility — Qualified expert — Independence and impartiality — Nature of expert’s duty to court — How expert’s duty relates to admissibility of expert’s evidence — Forensic accountant providing opinion on whether former auditors were negligent in performance of duties — Former auditors applying to strike out expert’s affidavit on grounds she was not impartial expert witness — Whether elements of expert’s duty to court go to admissibility of evidence rather than simply to its weight — If so, whether there is a threshold admissibility requirement in relation to independence and impartiality. The shareholders started a professional negligence action against the former auditors of their company after they had retained a different accounting firm, the Kentville office of GT, to perform various accounting tasks and which in their view revealed problems with the former auditors’ work. The auditors brought a motion for summary judgment seeking to have the shareholders’ action dismissed. In response, the shareholders retained M, a forensic accounting partner at the Halifax office of GT, to review all the relevant materials and to prepare a report of her findings. Her affidavit set out her findings, including her opinion that the auditors had not complied with their professional obligations to the shareholders. The auditors applied to strike out M’s affidavit on the grounds that she was not an impartial expert witness. The motions judge essentially agreed with the auditors and struck out M’s affidavit in its entirety. The majority of the Court of Appeal concluded that the motions judge erred in excluding M’s affidavit and allowed the appeal. Held : The appeal should be dismissed. The inquiry for determining the admissibility of expert opinion evidence is divided into two steps. At the first step, the proponent of the evidence must establish the threshold requirements of admissibility. These are the four factors set out in R. v. Mohan , 1994 80 (SCC) , [1994] 2 S.C.R. 9 (relevance, necessity, absence of an exclusionary rule and a properly qualified expert). Evidence that does not meet these threshold requirements should be excluded. At the second discretionary gatekeeping step, the trial judge must decide whether expert evidence that meets the preconditions to admissibility is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to the trial process that may flow from the admission of the expert evidence. Expert witnesses have a duty to the court to give fair, objective and non-partisan opinion evidence. They must be aware of this duty and able and willing to carry it out. The expert’s opinion must be impartial in the sense that it reflects an objective assessment of the questions at hand. It must be independent in the sense that it is the product of the expert’s independent judgment, uninfluenced by who has retained him or her or the outcome of the litigation. It must be unbiased in the sense that it does not unfairly favour one party’s position over another. The acid test is whether the expert’s opinion would not change regardless of which party retained him or her. These concepts, of course, must be applied to the realities of adversary litigation. Concerns related to the expert’s duty to the court and his or her willingness and capacity to comply with it are best addressed initially in the “qualified expert” element of the Mohan framework. A proposed expert witness who is unable or unwilling to fulfill his or her duty to the court is not properly qualified to perform the role of an expert. If the expert witness does not meet this threshold admissibility requirement, his or her evidence should not be admitted. Once this threshold is met, however, remaining concerns about an expert witness’s compliance with his or her duty should be considered as part of the overall cost-benefit analysis which the judge conducts to carry out his or her gatekeeping role. Imposing this additional threshold requirement is not intended to and should not result in trials becoming longer or more complex. The trial judge must determine, having regard to both the particular circumstances of the proposed expert and the substance of the proposed evidence, whether the expert is able and willing to carry out his or her primary duty to the court. Absent challenge, the expert’s attestation or testimony recognizing and accepting the duty will generally be sufficient to establish that this threshold is met. However, if a party opposing admissibility shows that there is a realistic concern that the expert is unable and/or unwilling to comply with his or her duty, the proponent of the evidence has the burden of establishing its admissibility. Exclusion at the threshold stage of the analysis should occur only in very clear cases in which the proposed expert is unable or unwilling to provide the court with fair, objective and non-partisan evidence. Anything less than clear unwillingness or inability to do so should not lead to exclusion, but be taken into account in the overall weighing of costs and benefits of receiving the evidence. The concept of apparent bias is not relevant to the question of whether or not an expert witness will be unable or unwilling to fulfill its primary duty to the court. When looking at an expert’s interest or relationship with a party, the question is not whether a reasonable observer would think that the expert is not independent. The question is whether the relationship or interest results in the expert being unable or unwilling to carry out his or her primary duty to the court to provide fair, non-partisan and objective assistance. In this case, there was no basis disclosed in the record to find that M’s evidence should be excluded because she was not able and willing to provide the court with fair, objective and non-partisan evidence. The majority of the Court of Appeal was correct in concluding that the motions judge committed a palpable and overriding error in determining that M was in a conflict of interest that prevented her from giving impartial and objective evidence. Cases Cited Applied: R. v. Mohan , 1994 80 (SCC) , [1994] 2 S.C.R. 9; Mouvement laïque québécois v. Saguenay (City) , 2015 SCC 16 , [2015] 2 S.C.R. 3; adopted: R. v. Abbey , 2009 ONCA 624 , 97 O.R. (3d) 330, leave to appeal refused, [2010] 2 S.C.R. v; referred to: Lord Abinger v. Ashton (1873), L.R. 17 Eq. 358; R. v. D.D. , 2000 SCC 43 , [2000] 2 S.C.R. 275; Graat v. The Queen , 1982 33 (SCC) , [1982] 2 S.C.R. 819; R. v. Abbey , 1982 25 (SCC) , [1982] 2 S.C.R. 24; R. v. J.-L.J. , 2000 SCC 51 , [2000] 2 S.C.R. 600; R. v. Sekhon , 2014 SCC 15 , [2014] 1 S.C.R. 272; Masterpiece Inc. v. Alavida Lifestyles Inc. , 2011 SCC 27 , [2011] 2 S.C.R. 387; R. v. Trochym , 2007 SCC 6 , [2007] 1 S.C.R. 239; R. v. Boswell , 2011 ONCA 283 , 85 C.R. (6th) 290; R. v. C. (M.) , 2014 ONCA 611 , 13 C.R. (7th) 396; National Justice Compania Naviera S.A. v. Prudential Assurance Co. , [1993] 2 Lloyd’s Rep. 68 , rev’d [1995] 1 Lloyd’s Rep. 455 ; Fellowes, McNeil v. Kansa General International Insurance Co. (1998), 1998 14856 (ON SC) , 40 O.R. (3d) 456; Royal Trust Corp. of Canada v. Fisherman (2000), 2000 22384 (ON SC) , 49 O.R. (3d) 187; R. v. Docherty , 2010 ONSC 3628 ; Ocean v. Economical Mutual Insurance Co. , 2010 NSSC 315 , 293 N.S.R. (2d) 394; Handley v. Punnett , 2003 BCSC 294 ; Bank of Montreal v. Citak , 2001 12419 (QC CQ) , [2001] O.J. No. 1096 (QL); Dean Construction Co. v. M.J. Dixon Construction Ltd. , 2011 ONSC 4629, 5 C.L.R. (4th) 240 ; Hutchingame v. Johnstone , 2006 BCSC 271 ; Alfano v. Piersanti , 2012 ONCA 297 , 291 O.A.C. 62; Kirby Lowbed Services Ltd. v. Bank of Nova Scotia , 2003 BCSC 617 ; Gould v. Western Coal Corp. , 2012 ONSC 5184 , 7 B.L.R. (5th) 19; United City Properties Ltd. v. Tong , 2010 BCSC 111 ; R. v. INCO Ltd. (2006), 2006 14962 (ON SC) , 80 O.R. (3d) 594; R. v. Klassen , 2003 MBQB 253 , 179 Man. R. (2d) 115; Gallant v. Brake-Patten , 2012 NLCA 23 , 321 Nfld. & P.E.I.R. 77; R. v. Violette , 2008 BCSC 920 ; Armchair Passenger Transport Ltd. v. Helical Bar Plc , [2003] EWHC 367; R. (Factortame Ltd.) v. Secretary of State for Transport , [2002] EWCA Civ 932, [2003] Q.B. 381; Gallaher International Ltd. v. Tlais Enterprises Ltd. , [2007] EWHC 464; Meat Corp. of Namibia Ltd. v. Dawn Meats (U.K.) Ltd. , [2011] EWHC 474; Matchbet Ltd. v. Openbet Retail Ltd. , [2013] EWHC 3067; FGT Custodians Pty. Ltd. v. Fagenblat , [2003] VSCA 33; Collins Thomson v. Clayton , [2002] NSWSC 366; Kirch Communications Pty Ltd. v. Gene Engineering Pty Ltd. , [2002] NSWSC 485; SmithKline Beecham (Australia) Pty Ltd. v. Chipman , [2003] FCA 796, 131 F.C.R. 500; Rodriguez v. Pacificare of Texas, Inc. , 980 F.2d 1014 (1993); Tagatz v. Marquette University , 861 F.2d 1040 (1988); Apple Inc. v. Motorola, Inc. , 757 F.3d 1286 (2014); Agribrands Purina Canada Inc. v. Kasamekas , 2010 ONSC 166 ; R. v. Demetrius , 2009 22797 ; International Hi-Tech Industries Inc. v. FANUC Robotics Canada Ltd. , 2006 BCSC 2011 ; Casurina Ltd. Partnership v. Rio Algom Ltd. (2002), 2002 9356 (ON SC) , 28 B.L.R. (3d) 44; Prairie Well Servicing Ltd. v. Tundra Oil and Gas Ltd. , 2000 MBQB 52 , 146 Man. R. (2d) 284; Deemar v. College of Veterinarians of Ontario , 2008 ONCA 600 , 92 O.R. (3d) 97; Coady v. Burton Canada Co. , 2013 NSCA 95 , 333 N.S.R. (2d) 348; Fougere v. Blunden Construction Ltd. , 2014 NSCA 52 , 345 N.S.R. (2d) 385. Statutes and Regulations Cited Act to establish the new Code of Civil Procedure , S.Q. 2014, c. 1, arts. 22, 235 [not yet in force]. Civil Procedure Rules (Nova Scotia), rr. 55.01(2), 55.04(1)(a), (b), (c). Federal Courts Rules , SOR/98-106, r. 52.2(1)( c ). Queen’s Bench Rules (Saskatchewan), r. 5-37. Rules of Civil Procedure , R.R.O. 1990, Reg. 194, rr. 4.1.01(1), (2), 53.03(2.1). Rules of Civil Procedure (Prince Edward Island), r. 53.03(3) (g). Rules of Court , Y.O.I.C. 2009/65, r. 34(23). Supreme Court Civil Rules , B.C. Reg. 168/2009, rr. 11-2(1), (2). Authors Cited Anderson, Glenn R. Expert Evidence , 3rd ed. Markham, Ont.: LexisNexis, 2014. Béchard, Donald, avec la collaboration de Jessica Béchard. L’expert . Cowansville, Qué.: Yvon Blais, 2011. Canadian Encyclopedic Digest , Ontario 4th ed., vol. 24. Toronto: Carswell, 2014 (loose-leaf updated 2014, release 6). Chamberland, Luc. Le nouveau Code de procédure civile commenté . Cowansville, Qué.: Yvon Blais, 2014. Corpus Juris Secundum , vol. 32. Eagan, Minn.: Thomson West, 2008. Cross and Tapper on Evidence , 12th ed. by Colin Tapper. Oxford: Oxford University Press, 2010. Freckelton, Ian, and Hugh Selby. Expert Evidence: Law, Practice, Procedure and Advocacy , 5th ed. Pyrmont, N.S.W.: Lawbook Co., 2013. Halsbury’s Laws of Canada: Evidence , 2014 Reissue, contributed by Hamish C. Stewart. Markham, Ont.: LexisNexis, 2014. Lederman, Sidney N., Alan W. Bryant and Michelle K. Fuerst. The Law of Evidence in Canada , 4th ed. Markham, Ont.: LexisNexis, 2014. McWilliams’ Canadian Criminal Evidence , 5th ed. by S. Casey Hill, David M. Tanovich and Louis P. Strezos, eds. 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Phipson on Evidence , 18th ed. by Hodge M. Malek et al., eds. London: Sweet & Maxwell, 2013. Royer, Jean-Claude, et Sophie Lavallée. La preuve civile , 4 e éd. Cowansville, Qué.: Yvon Blais, 2008. Thayer, James Bradley. A Preliminary Treatise on Evidence at the Common Law . Boston: Little, Brown and Co., 1898 (reprinted South Hackensack, N.J.: Rothman Reprints, Inc., 1969). United Kingdom. Access to Justice: Final Report (Woolf Report). London: HMSO, 1996. APPEAL from a judgment of the Nova Scotia Court of Appeal (MacDonald C.J. and Oland and Beveridge JJ.A.), 2013 NSCA 66 , 330 N.S.R. (2d) 301, 361 D.L.R. (4th) 659, 36 C.P.C. (7th) 22, [2013] N.S.J. No. 259 (QL), 2013 CarswellNS 360 (WL Can.), setting aside in part a decision of Pickup J., 2012 NSSC 210 , 317 N.S.R. (2d) 283, 26 C.P.C. (7th) 280, [2012] N.S.J. No. 289 (QL), 2012 CarswellNS 376 (WL Can.). Appeal dismissed. Alan D’Silva , James Wilson and Aaron Kreaden , for the appellants. Jon Laxer and Brian F. P. Murphy , for the respondents. Michael H. Morris , for the intervener the Attorney General of Canada. Matthew Gourlay , for the intervener the Criminal Lawyers’ Association (Ontario). The judgment of the Court was delivered by Cromwell J. — I. Introduction and Issues [ 1 ] Expert opinion evidence can be a key element in the search for truth, but it may also pose special dangers. To guard against them, the Court over the last 20 years or so has progressively tightened the rules of admissibility and enhanced the trial judge’s gatekeeping role. These developments seek to ensure that expert opinion evidence meets certain basic standards before it is admitted. The question on this appeal is whether one of these basic standards for admissibility should relate to the proposed expert’s independence and impartiality. In my view, it should. [ 2 ] Expert witnesses have a special duty to the court to provide fair, objective and non-partisan assistance. A proposed expert witness who is unable or unwilling to comply with this duty is not qualified to give expert opinion evidence and should not be permitted to do so. Less fundamental concerns about an expert’s independence and impartiality should be taken into account in the broader, overall weighing of the costs and benefits of receiving the evidence. [ 3 ] Applying these principles, I agree with the conclusion reached by the majority of the Nova Scotia Court of Appeal and would therefore dismiss this appeal with costs. II. Overview of the Facts and Judicial History A. Facts and Proceedings [ 4 ] The appeal arises out of a professional negligence action by the respondents (who I will call the shareholders) against the appellants, the former auditors of their company (I will refer to them as the auditors). The shareholders started the action after they had retained a different accounting firm, the Kentville office of Grant Thornton LLP, to perform various accounting tasks and which in their view revealed problems with the auditors’ previous work. The central allegation in the action is that the auditors’ failure to apply generally accepted auditing and accounting standards while carrying out their functions caused financial loss to the shareholders. The main question in the action boils down to whether the auditors were negligent in the performance of their professional duties. [ 5 ] The auditors brought a motion for summary judgment in August of 2010, seeking to have the shareholders’ action dismissed. In response, the shareholders retained Susan MacMillan, a forensic accounting partner at the Halifax office of Grant Thornton, to review all the relevant materials, including the documents filed in the action, and to prepare a report of her findings. Her affidavit set out her findings, including her opinion that the auditors had not complied with their professional obligations to the shareholders. The auditors applied to strike out Ms. MacMillan’s affidavit on the grounds that she was not an impartial expert witness. They argued that the action comes down to a battle of opinion between two accounting firms — the auditors’ and the expert witness’s. Ms. MacMillan’s firm could be exposed to liability if its approach was not accepted by the court and, as a partner, Ms. MacMillan could be personally liable. Her potential liability if her opinion were not accepted gives her a personal financial interest in the outcome of the litigations and this, in the auditors’ submission, ought to disqualify her from testifying. [ 6 ] The proceedings since have been neither summary nor resulted in a judgment. Instead, the litigation has been focused on the expert evidence issue; the summary judgment application has not yet been heard on its merits. B. Judgments Below (1) Nova Scotia Supreme Court: 2012 NSSC 210 , 317 N.S.R. (2d) 283 (Pickup J.) [ 7 ] Pickup J. essentially agreed with the auditors and struck out the MacMillan affidavit in its entirety: para. 106. He found that, in order to be admissible, an expert’s evidence “must be, and be seen to be, independent and impartial”: para. 99. Applying that test, he concluded that this was one of those “clearest of cases where the reliability of the expert . . . does not meet the threshold requirements for admissibility”: para. 101. (2) Nova Scotia Court of Appeal: 2013 NSCA 66 , 330 N.S.R. (2d) 301 (Beveridge J.A., Oland J.A. Concurring; MacDonald C.J.N.S. Dissenting) [ 8 ] The majority of the Court of Appeal concluded that the motions judge erred in excluding Ms. MacMillan’s affidavit. Beveridge J.A. wrote that while the court has discretion to exclude expert evidence due to actual bias or partiality, the test adopted by the motions judge — that an expert “must be, and be seen to be, independent and impartial” — was wrong in law. He ought not to have ruled her evidence inadmissible and struck out her affidavit. [ 9 ] MacDonald C.J.N.S., dissenting, would have upheld the motions judge’s decision because he had properly articulated and applied the relevant legal principles. III. Analysis A. Overview [ 10 ] In my view, expert witnesses have a duty to the court to give fair, objective and non-partisan opinion evidence. They must be aware of this duty and able and willing to carry it out. If they do not meet this threshold requirement, their evidence should not be admitted. Once this threshold is met, however, concerns about an expert witness’s independence or impartiality should be considered as part of the overall weighing of the costs and benefits of admitting the evidence. This common law approach is, of course, subject to statutory and related provisions which may establish different rules of admissibility. B. Expert Witness Independence and Impartiality [ 11 ] There have been long-standing concerns about whether expert witnesses hired by the parties are impartial in the sense that they are expressing their own unbiased professional opinion and whether they are independent in the sense that their opinion is the product of their own, independent conclusions based on their own knowledge and judgment: see, e.g., G. R. Anderson, Expert Evidence (3rd ed. 2014), at p. 509; S. N. Lederman, A. W. Bryant and M. K. Fuerst, The Law of Evidence in Canada (4th ed. 2014), at p. 783. As Sir George Jessel, M.R., put it in the 1870s, “[u]ndoubtedly there is a natural bias to do something serviceable for those who employ you and adequately remunerate you. It is very natural, and it is so effectual, that we constantly see persons, instead of considering themselves witnesses, rather consider themselves as the paid agents of the person who employs them”: Lord Abinger v. Ashton (1873), L.R. 17 Eq. 358, at p. 374. [ 12 ] Recent experience has only exacerbated these concerns; we are now all too aware that an expert’s lack of independence and impartiality can result in egregious miscarriages of justice: R. v. D.D. , 2000 SCC 43 , [2000] 2 S.C.R. 275, at para. 52 . As observed by Beveridge J.A. in this case, T he Commission on Proceedings Involving Guy Paul Morin: Report ( 1998) authored by the Honourable Fred Kaufman and the Inquiry into Pediatric Forensic Pathology in Ontario: Report (2008) conducted by the Honourable Stephen T. Goudge provide two striking examples where “[s]eemingly solid and impartial, but flawed, forensic scientific opinion has played a prominent role in miscarriages of justiceˮ: para. 105. Other reports outline the critical need for impartial and independent expert evidence in civil litigation: ibid. , at para. 106; see the Right Honourable Lord Woolf, Access to Justice: Final Report (1996); the Honourable Coulter A. Osborne, Civil Justice Reform Project: Summary of Findings & Recommendations (2007). [ 13 ] To decide how our law of evidence should best respond to these concerns, we must confront several questions: Should concerns about potentially biased expert opinion go to admissibility or only to weight?; If to admissibility, should these concerns be addressed by a threshold requirement for admissibility, by a judicial discretion to exclude, or both?; At what point do these concerns justify exclusion of the evidence?; And finally, how is our response to these concerns integrated into the existing legal framework governing the admissibility of expert opinion evidence? To answer these questions, we must first consider the existing legal framework governing admissibility, identify the duties that an expert witness has to the court and then turn to how those duties are best reflected in that legal framework. C. The Legal Framework (1) The Exclusionary Rule for Opinion Evidence [ 14 ] To the modern general rule that all relevant evidence is admissible there are many qualifications. One of them relates to opinion evidence, which is the subject of a complicated exclusionary rule. Witnesses are to testify as to the facts which they perceived, not as to the inferences — that is, the opinions — that they drew from them. As one great evidence scholar put it long ago, it is “for the jury to form opinions, and draw inferences and conclusions, and not for the witness”: J. B. Thayer, A Preliminary Treatise on Evidence at the Common Law (1898; reprinted 1969), at p. 524; see also C. Tapper, Cross and Tapper on Evidence (12th ed. 2010), at p. 530. While various rationales have been offered for this exclusionary rule, the most convincing is probably that these ready-formed inferences are not helpful to the trier of fact and might even be misleading: see, e.g., Graat v. The Queen , 1982 33 (SCC) , [1982] 2 S.C.R. 819, at p. 836; Halsbury’s Laws of Canada: Evidence (2014 Reissue), at para. HEV-137 “General rule against opinion evidence”. [ 15 ] Not all opinion evidence is excluded, however. Most relevant for this case is the exception for expert opinion evidence on matters requiring specialized knowledge. As Prof. Tapper put it, “the law recognizes that, so far as matters calling for special knowledge or skill are concerned, judges and jurors are not necessarily equipped to draw true inferences from facts stated by witnesses. A witness is therefore allowed to state his opinion about such matters, provided he is expert in them”: p. 530; see also R. v. Abbey , 1982 25 (SCC) , [1982] 2 S.C.R. 24, at p. 42. (2) The Current Legal Framework for Expert Opinion Evidence [ 16 ] Since at least the mid-1990s, the Court has responded to a number of concerns about the impact on the litigation process of expert evidence of dubious value. The jurisprudence has clarified and tightened the threshold requirements for admissibility, added new requirements in order to assure reliability, particularly of novel scientific evidence, and emphasized the important role that judges should play as “gatekeepers” to screen out proposed evidence whose value does not justify the risk of confusion, time and expense that may result from its admission. [ 17 ] We can take as the starting point for these developments the Court’s decision in R. v. Mohan , 1994 80 (SCC) , [1994] 2 S.C.R. 9. That case described the potential dangers of expert evidence and established a four-part threshold test for admissibility. The dangers are well known. One is that the trier of fact will inappropriately defer to the expert’s opinion rather than carefully evaluate it. As Sopinka J. observed in Mohan : There is a danger that expert evidence will be misused and will distort the fact-finding process. Dressed up in scientific language which the jury does not easily understand and submitted through a witness of impressive antecedents, this evidence is apt to be accepted by the jury as being virtually infallible and as having more weight than it deserves. [p. 21] (See also D.D. , at para. 53 ; R. v. J.-L.J. , 2000 SCC 51 , [2000] 2 S.C.R. 600, at paras. 25-26 ; R. v. Sekhon , 2014 SCC 15 , [2014] 1 S.C.R. 272, at para. 46 .) [ 18 ] The point is to preserve trial by judge and jury, not devolve to trial by expert. There is a risk that the jury “will be unable to make an effective and critical assessment of the evidenceˮ: R. v. Abbey , 2009 ONCA 624 , 97 O.R. (3d) 330, at para. 90 , leave to appeal refused, [2010] 2 S.C.R. v. The trier of fact must be able to use its “informed judgment”, not simply decide on the basis of an “act of faith” in the expert’s opinion: J.-L.J. , at para. 56 . The risk of “attornment to the opinion of the expertˮ is also exacerbated by the fact that expert evidence is resistant to effective cross-examination by counsel who are not experts in that field: D.D. , at para. 54 . The cases address a number of other related concerns: the potential prejudice created by the expert’s reliance on unproven material not subject to cross-examination ( D.D. , at para. 55 ); the risk of admitting “junk science” ( J.-L.J. , at para. 25 ); and the risk that a “contest of experts” distracts rather than assists the trier of fact ( Mohan , at p. 24). Another well-known danger associated with the admissibility of expert evidence is that it may lead to an inordinate expenditure of time and money: Mohan , at p. 21; D.D. , at para. 56 ; Masterpiece Inc. v. Alavida Lifestyles Inc. , 2011 SCC 27 , [2011] 2 S.C.R. 387, at para. 76 . [ 19 ] To address these dangers, Mohan established a basic structure for the law relating to the admissibility of expert opinion evidence. That structure has two main components. First, there are four threshold requirements that the proponent of the evidence must establish in order for proposed expert opinion evidence to be admissible: (1) relevance; (2) necessity in assisting the trier of fact; (3) absence of an exclusionary rule; and (4) a properly qualified expert ( Mohan , at pp. 20-25; see also Sekhon , at para. 43 ). Mohan also underlined the important role of trial judges in assessing whether otherwise admissible expert evidence should be excluded because its probative value was overborne by its prejudicial effect — a residual discretion to exclude evidence based on a cost-benefit analysis: p. 21. This is the second component, which the subsequent jurisprudence has further emphasized: Lederman, Bryant and Fuerst, at pp. 789-90; J. - L.J. , at para. 28 . [ 20 ] Mohan and the jurisprudence since, however, have not explicitly addressed how this “cost-benefit” component fits into the overall analysis. The reasons in Mohan engaged in a cost-benefit analysis with respect to particular elements of the four threshold requirements, but they also noted that the cost-benefit analysis could be an aspect of exercising the overall discretion to exclude evidence whose probative value does not justify its admission in light of its potentially prejudicial effects: p. 21. The jurisprudence since Mohan has also focused on particular aspects of expert opinion evidence, but again without always being explicit about where additional concerns fit into the analysis. The unmistakable overall trend of the jurisprudence, however, has been to tighten the admissibility requirements and to enhance the judge’s gatekeeping role. [ 21 ] So, for example, the necessity threshold criterion was emphasized in cases such as D.D. The majority underlined that the necessity requirement exists “to ensure that the dangers associated with expert evidence are not lightly tolerated” and that “[m]ere relevance or ‘helpfulness’ is not enough”: para. 46. Other cases have addressed the reliability of the science underlying an opinion and indeed technical evidence in general: J.-L.J. ; R. v. Trochym , 2007 SCC 6 , [2007] 1 S.C.R. 239. The question remains, however, as to where the cost-benefit analysis and concerns such as those about reliability fit into the overall analysis. [ 22 ] Abbey (ONCA) introduced helpful analytical clarity by dividing the inquiry into two steps. With minor adjustments, I would adopt that approach. [ 23 ] At the first step, the proponent of the evidence must establish the threshold requirements of admissibility. These are the four Mohan factors (relevance, necessity, absence of an exclusionary rule and a properly qualified expert) and in addition, in the case of an opinion based on novel or contested science or science used for a novel purpose, the reliability of the underlying science for that purpose: J.-L.J. , at paras. 33, 35-36 and 47 ; Trochym , at para. 27 ; Lederman, Bryant and Fuerst, at pp. 788-89 and 800-801. Relevance at this threshold stage refers to logical relevance: Abbey (ONCA), at para. 82; J.-L.J. , at para. 47 . Evidence that does not meet these threshold requirements should be excluded. Note that I would retain necessity as a threshold requirement: D.D. , at para. 57 ; see D. M. Paciocco and L. Stuesser, The Law of Evidence (7th ed. 2015), at pp. 209-10; R. v. Boswell , 2011 ONCA 283 , 85 C.R. (6th) 290, at para. 13 ; R. v. C. (M.) , 2014 ONCA 611 , 13 C.R. (7th) 396, at para. 72 . [ 24 ] At the second discretionary gatekeeping step, the judge balances the potential risks and benefits of admitting the evidence in order to decide whether the potential benefits justify the risks. The required balancing exercise has been described in various ways. In Mohan , Sopinka J. spoke of the “reliability versus effect factor” (p. 21), while in J.-L.J. , Binnie J. spoke about “relevance, reliability and necessity” being “measured against the counterweights of consumption of time, prejudice and confusion”: para. 47. Doherty J.A. summed it up well in Abbey , stating that the “trial judge must decide whether expert evidence that meets the preconditions to admissibility is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to the trial process that may flow from the admission of the expert evidence”: para. 76. [ 25 ] With this delineation of the analytical framework, we can turn to the nature of an expert’s duty to the court and where it fits into that framework. D. The Expert’s Duty to the Court or Tribunal [ 26 ] There is little controversy about the broad outlines of the expert witness’s duty to the court. As Anderson writes, “[t]he duty to provide independent assistance to the Court by way of objective unbiased opinion has been stated many times by common law courts around the world”: p. 227. I would add that a similar duty exists in the civil law of Quebec: J.-C. Royer and S. Lavallée, La preuve civile (4th ed. 2008), at para. 468; D. Béchard, with the collaboration of J. Béchard, L’expert ( 2011), c. 9 ; An Act to establish the new Code of Civil Procedure , S.Q. 2014, c. 1, art. 22 (not yet in force); L. Chamberland, Le nouveau Code de procédure civile commenté (2014), at pp. 14 and 121. [ 27 ] One influential statement of the elements of this duty are found in the English case National Justice Compania Naviera S.A. v. Prudential Assurance Co. , [1993] 2 Lloyd’s Rep. 68 (Q.B.) . Following an 87-day trial, Cresswell J. believed that a misunderstanding of the duties and responsibilities of expert witnesses contributed to the length of the trial. He listed in obiter dictum duties and responsibilities of experts, the first two of which have particularly influenced the development of Canadian law:

1. Expert evidence presented to the Court should be, and should be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of litigation . . . .
2. An expert witness should provide independent assistance to the Court by way of objective unbiased opinion in relation to matters within his [or her] expertise . . . . An expert witness in the High Court should never assume the role of an advocate. [Emphasis added; citation omitted; p. 81.] (These duties were endorsed on appeal: [1995] 1 Lloyd’s Rep. 455 (C.A.), at p. 496 .) [ 28 ] Many provinces and territories have provided explicit guidance related to the duty of expert witnesses. In Nova Scotia, for example, the Civil Procedure Rules require that an expert’s report be signed by the expert who must make (among others) the following representations to the court: that the expert is providing an objective opinion for the assistance of the court; that the expert is prepared to apply independent judgment when assisting the court; and that the report includes everything the expert regards as relevant to the expressed opinion and draws attention to anything that could reasonably lead to a different conclusion ( r. 55.04(1) (a), (b) and (c)). While these requirements do not affect the rules of evidence by which expert opinion is determined to be admissible or inadmissible, they provide a convenient summary of a fairly broadly shared sense of the duties of an expert witness to the court. [ 29 ] There are similar descriptions of the expert’s duty in the civil procedure rules in other Canadian jurisdictions: Anderson, at p. 227; The Queen’s Bench Rules (Saskatchewan), r. 5-37; Supreme Court Civil Rules , B.C. Reg. 168/2009, r. 11-2(1); Rules of Civil Procedure , R.R.O. 1990, Reg. 194, r. 4.1.01(1); Rules of Court , Y.O.I.C. 2009/65, r. 34(23); An Act to establish the new Code of Civil Procedure , art. 22. Moreover, the rules in Saskatchewan, British Columbia, Ontario, Nova Scotia, Prince Edward Island, Quebec and the Federal Courts require experts to certify that they are aware of and will comply with their duty to the court: Anderson, at p. 228; Saskatchewan Queen’s Bench Rules , r. 5-37(3); British Columbia Supreme Court Civil Rules , r. 11-2(2); Ontario Rules of Civil Procedure , r. 53.03(2.1); Nova Scotia Civil Procedure Rules , r. 55.04(1)(a); Prince Edward Island Rules of Civil Procedure , r. 53.03(3)(g); An Act to establish the new Code of Civil Procedure , art. 235 (not yet in force); Federal Courts Rules , SOR/98-106, r. 52.2(1)( c ). [ 30 ] The formulation in the Ontario Rules of Civil Procedure is perhaps the most succinct and complete statement of the expert’s duty to the court: to provide opinion evidence that is fair, objective and non-partisan ( r. 4.1.01(1) (a)). The Rules are also explicit that this duty to the court prevails over any obligation owed by the expert to a party ( r. 4.1.01(2) ). Likewise, the newly adopted Act to establish the new Code of Civil Procedure of Quebec explicitly provides, as a guiding principle, that the expert’s duty to the court overrides the parties’ interests, and that the expert must fulfill his or her primary duty to the court “objectively, impartially and thoroughly”: art. 22; Chamberland, at pp. 14 and 121. [ 31 ] Many of the relevant rules of court simply reflect the duty that an expert witness owes to the court at common law: Anderson, at p. 227. In my opinion, this is true of the Nova Scotia rules that apply in this case. Of course, it is always open to each jurisdiction to impose different rules of admissibility, but in the absence of a clear indication to that effect, the common law rules apply in common law cases. I note that in Nova Scotia, the Civil Procedure Rules explicitly provide that they do not change the rules of evidence by which the admissibility of expert opinion evidence is determined: r. 55.01(2) . [ 32 ] Underlying the various formulations of the duty are three related concepts: impartiality, independence and absence of bias. The expert’s opinion must be impartial in the sense that it reflects an objective assessment of the questions at hand. It must be independent in the sense that it is the product of the expert’s independent judgment, uninfluenced by who has retained him or her or the outcome of the litigation. It must be unbiased in the sense that it does not unfairly favour one party’s position over another. The acid test is whether the expert’s opinion would not change regardless of which party retained him or her: P. Michell and R. Mandhane, “The Uncertain Duty of the Expert Witness” (2005), 42 Alta. L. Rev. 635, at pp. 638-39. These concepts, of course, must be applied to the realities of adversary litigation. Experts are generally retained, instructed and paid by one of the adversaries. These facts alone do not undermine the expert’s independence, impartiality and freedom from bias. E. The Expert’s Duties and Admissibility [ 33 ] As we have seen, there is a broad consensus about the nature of an expert’s duty to the court. There is no such consensus, however, about how that duty relates to the admissibility of an expert’s evidence. There are two main questions: Should the elements of this duty go to admissibility of the evidence rather than simply to its weight?; And, if so, is there a threshold admissibility requirement in relation to independence and impartiality? [ 34 ] In this section, I will explain my view that the answer to both questions is yes: a proposed expert’s independence and impartiality go to admissibility and not simply to weight and there is a threshold admissibility requirement in relation to this duty. Once that threshold is met, remaining concerns about the expert’s compliance with his or her duty should be considered as part of the overall cost-benefit analysis which the judge conducts to carry out his or her gatekeeping role. (1) Admissibility or Only Weight? (a) The Canadian Law [ 35 ] The weight of authority strongly supports the conclusion that at a certain point, expert evidence should be ruled inadmissible due to the expert’s lack of impartiality and/or independence. [ 36 ] Our Court has confirmed this position in a recent decision that was not available to the courts below: It is well established that an expert’s opinion must be independent, impartial and objective, and given with a view to providing assistance to the decision maker (J. ‑ C. Royer and S. Lavallée, La preuve civile (4th ed. 2008), at No. 468; D. Béchard, with the collaboration of J. Béchard, L’expert ( 2011), chap. 9 ; An Act to establish the new Code of Civil Procedure , S.Q. 2014, c. 1, s. 22 (not yet in force)). However, these factors generally have an impact on the probative value of the expert’s opinion and are not always insurmountable barriers to the admissibility of his or her testimony. Nor do they necessarily “disqualify” the expert (L. Ducharme and C.-M. Panaccio, L’administration de la preuve (4th ed. 2010), at Nos. 590 ‑ 91 and 605). For expert testimony to be inadmissible, more than a simple appearance of bias is necessary. The question is not whether a reasonable person would consider that the expert is not independent. Rather, what must be determined is whether the expert’s lack of independence renders him or her incapable of giving an impartial opinion in the specific circumstances of the case (D. M. Paciocco, “Unplugging Jukebox Testimony in an Adversarial System: Strategies for Changing the Tune on Partial Experts” (2009), 34 Queen’s L.J. 565, at pp. 598-99). ( Mouvement laïque québécois v. Saguenay (City) , 2015 SCC 16 , [2015] 2 S.C.R. 3, at para. 106 ) [ 37 ] I will refer to a number of other cases that support this view. I do so by way of illustration and without commenting on the outcome of particular cases. An expert’s interest in the litigation or relationship to the parties has led to exclusion in a number of cases: see, e.g., Fellowes, McNeil v. Kansa General International Insurance Co. (1998), 1998 14856 (ON SC) , 40 O.R. (3d) 456 (Gen. Div.) (proposed expert was the defendant’s lawyer in related matters and had investigated from the outset of his retainer the matter of a potential negligence claim against the plaintiff); Royal Trust Corp. of Canada v. Fisherman (2000), 2000 22384 (ON SC) , 49 O.R. (3d) 187 (S.C.J.) (expert was the party’s lawyer in related U.S. proceedings); R. v. Docherty , 2010 ONSC 3628 (expert was the defence counsel’s father); Ocean v. Economical Mutual Insurance Co. , 2010 NSSC 315 , 293 N.S.R. (2d) 394 (expert was also a party to the litigation); Handley v. Punnett , 2003 BCSC 294 (expert was also a party to the litigation); Bank of Montreal v. Citak , 2001 12419 (QC CQ) , [2001] O.J. No. 1096 (QL) (S.C.J.) (expert was effectively a “co-venturer” in the case due in part to the fact that 40 percent of his remuneration was contingent upon success at trial: para. 7); Dean Construction Co. v. M.J. Dixon Construction Ltd. , 2011 ONSC 4629, 5 C.L.R. (4th) 240 (expert’s retainer agreement was inappropriate); Hutchingame v. Johnstone , 2006 BCSC 271 (expert stood to incur liability depending on the result of the trial). In other cases, the expert’s stance or behaviour as an advocate has justified exclusion: see, e.g., Alfano v. Piersanti , 2012 ONCA 297 , 291 O.A.C. 62; Kirby Lowbed Services Ltd. v. Bank of Nova Scotia , 2003 BCSC 617 ; Gould v. Western Coal Corp. , 2012 ONSC 5184 , 7 B.L.R. (5th) 19. [ 38 ] Many other cases have accepted, in principle, that lack of independence or impartiality can lead to exclusion, but have ruled that the expert evidence did not warrant rejection on the particular facts: see, e.g., United City Properties Ltd. v. Tong , 2010 BCSC 111 ; R. v. INCO Ltd. (2006), 2006 14962 (ON SC) , 80 O.R. (3d) 594 (S.C.J.). This was the position of the Court of Appeal in this case: para. 109; see also para. 121. [ 39 ] Some Canadian courts, however, have treated these matters as going exclusively to weight rather than to admissibility. The most often cited cases for this proposition are probably R. v. Klassen , 2003 MBQB 253 , 179 Man. R. (2d) 115, and Gallant v. Brake-Patten , 2012 NLCA 23 , 321 Nfld. & P.E.I.R. 77. Klassen holds as admissible any expert evidence meeting the criteria from Mohan , with bias only becoming a factor as to the weight to be given to the evidence: see also R. v. Violette , 2008 BCSC 920 . Similarly, the court in Gallant determined that a challenge to expert evidence that is based on the expert having a connection to a party or an issue in the case or a possible predetermined position on the case cannot take place at the admissibility stage: para. 89. [ 40 ] I conclude that the dominant approach in Canadian common law is to treat independence and impartiality as bearing not just on the weight but also on the admissibility of the evidence. I note that while the shareholders submit that issues regarding expert independence should go only to weight, they rely on cases such as INCO that specifically accept that a finding of lack of independence or impartiality can lead to inadmissibility in certain circumstances: R.F., at paras. 52-53. (b) Other Jurisdictions [ 41 ] Outside Canada, the concerns related to independence and impartiality have been addressed in a number of ways. Some are similar to the approach in Canadian law. [ 42 ] For example, summarizing the applicable principles in British law, Nelson J. in Armchair Passenger Transport Ltd. v. Helical Bar Plc , [2003] EWHC 367 (Q.B.), underlined that when an expert has an interest or connection with the litigation or a party thereto, exclusion will be warranted if it is determined that the expert is unwilling or unable to carry out his or her primary duty to the court: see also H. M. Malek et al., eds., Phipson on Evidence (18th ed. 2013), at pp. 1158-59. The mere fact of an interest or connection will not disqualify, but it nonetheless may do so in light of the nature and extent of the interest or connection in particular circumstances. As Lord Phillips of Worth Matravers, M.R., put it in a leading case, “[i]t is always desirable that an expert should have no actual or apparent interest in the outcome of the proceedings in which he gives evidence, but such disinterest is not automatically a precondition to the admissibility of his evidence”: R. (Factortame Ltd.) v. Secretary of State for Transport , [2002] EWCA Civ 932, [2003] Q.B. 381, at para. 70; see also Gallaher International Ltd. v. Tlais Enterprises Ltd. , [2007] EWHC 464 (Comm.); Meat Corp. of Namibia Ltd. v. Dawn Meats (U.K.) Ltd. , [2011] EWHC 474 (Ch. D.); Matchbet Ltd. v. Openbet Retail Ltd. , [2013] EWHC 3067 (Ch. D.), at paras. 312-17. [ 43 ] In Australia, the expert’s objectivity and impartiality will generally go to weight, not to admissibility: I. Freckelton and H. Selby, Expert Evidence: Law, Practice, Procedure and Advocacy (5th ed. 2013), at p. 35. As the Court of Appeal of the State of Victoria put it: “. . . to the extent that it is desirable that expert witnesses should be under a duty to assist the Court, that has not been held and should not be held as disqualifying, in itself, an ‘interested’ witness from being competent to give expert evidence” ( FGT Custodians Pty. Ltd. v. Fagenblat , [2003] VSCA 33, at para. 26 (AustLII); see also Freckelton and Selby, at pp. 186-88; Collins Thomson v. Clayton , [2002] NSWSC 366; Kirch Communications Pty Ltd. v. Gene Engineering Pty Ltd. , [2002] NSWSC 485; SmithKline Beecham (Australia) Pty Ltd. v. Chipman , [2003] FCA 796, 131 F.C.R. 500). [ 44 ] In the United States, at the federal level, the independence of the expert is a consideration that goes to the weight of the evidence, and a party may testify as an expert in his own case: Rodriguez v. Pacificare of Texas, Inc. , 980 F.2d 1014 (5th Cir. 1993), at p. 1019; Tagatz v. Marquette University , 861 F.2d 1040 (7th Cir. 1988); Apple Inc. v. Motorola, Inc. , 757 F.3d 1286 (Fed. Cir. 2014), at p. 1321 . This also seems to be a fair characterization of the situation in the states ( Corpus Juris Secundum , vol. 32 (2008), at p. 325: “The bias or interest of the witness does not affect his or her qualification, but only the weight to be given the testimony.”). (c) Conclusion [ 45 ] Following what I take to be the dominant view in the Canadian cases, I would hold that an expert’s lack of independence and impartiality goes to the admissibility of the evidence in addition to being considered in relation to the weight to be given to the evidence if admitted. That approach seems to me to be more in line with the basic structure of our law relating to expert evidence and with the importance our jurisprudence has attached to the gatekeeping role of trial judges. Binnie J. summed up the Canadian approach well in J.-L.J. : “The admissibility of the expert evidence should be scrutinized at the time it is proffered, and not allowed too easy an entry on the basis that all of the frailties could go at the end of the day to weight rather than admissibility” (para. 28). (2) The Appropriate Threshold [ 46 ] I have already described the duty owed by an expert witness to the court: the expert must be fair, objective and non-partisan. As I see it, the appropriate threshold for admissibility flows from this duty. I agree with Prof. (now Justice of the Ontario Court of Justice) Paciocco that “the common law has come to accept . . . that expert witnesses have a duty to assist the court that overrides their obligation to the party calling them. If a witness is unable or unwilling to fulfill that duty, they do not qualify to perform the role of an expert and should be excluded”: “Taking a ‘Goudge’ out of Bluster and Blarney: an ‘Evidence-Based Approach’ to Expert Testimony” (2009), 13 Can. Crim. L.R. 135, at p. 152 (footnote omitted). The expert witnesses must, therefore, be aware of this primary duty to the court and able and willing to carry it out. [ 47 ] Imposing this additional threshold requirement is not intended to and should not result in trials becoming longer or more complex. As Prof. Paciocco aptly observed, “if inquiries about bias or partiality become routine during Mohan voir dires , trial testimony will become nothing more than an inefficient reprise of the admissibility hearing”: “Unplugging Jukebox Testimony in an Adversarial System: Strategies for Changing the Tune on Partial Experts” (2009), 34 Queen’s L.J. 565 (“Jukeboxˮ), at p. 597. While I would not go so far as to hold that the expert’s independence and impartiality should be presumed absent challenge, my view is that absent such challenge, the expert’s attestation or testimony recognizing and accepting the duty will generally be sufficient to establish that this threshold is met. [ 48 ] Once the expert attests or testifies on oath to this effect, the burden is on the party opposing the admission of the evidence to show that there is a realistic concern that the expert’s evidence should not be received because the expert is unable and/or unwilling to comply with that duty. If the opponent does so, the burden to establish on a balance of probabilities this aspect of the admissibility threshold remains on the party proposing to call the evidence. If this is not done, the evidence, or those parts of it that are tainted by a lack of independence or impartiality, should be excluded. This approach conforms to the general rule under the Mohan framework, and elsewhere in the law of evidence, that the proponent of the evidence has the burden of establishing its admissibility. [ 49 ] This threshold requirement is not particularly onerous and it will likely be quite rare that a proposed expert’s evidence would be ruled inadmissible for failing to meet it. The trial judge must determine, having regard to both the particular circumstances of the proposed expert and the substance of the proposed evidence, whether the expert is able and willing to carry out his or her primary duty to the court. For example, it is the nature and extent of the interest or connection with the litigation or a party thereto which matters, not the mere fact of the interest or connection; the existence of some interest or a relationship does not automatically render the evidence of the proposed expert inadmissible. In most cases, a mere employment relationship with the party calling the evidence will be insufficient to do so. On the other hand, a direct financial interest in the outcome of the litigation will be of more concern. The same can be said in the case of a very close familial relationship with one of the parties or situations in which the proposed expert will probably incur professional liability if his or her opinion is not accepted by the court. Similarly, an expert who, in his or her proposed evidence or otherwise, assumes the role of an advocate for a party is clearly unwilling and/or unable to carry out the primary duty to the court. I emphasize that exclusion at the threshold stage of the analysis should occur only in very clear cases in which the proposed expert is unable or unwilling to provide the court with fair, objective and non-partisan evidence. Anything less than clear unwillingness or inability to do so should not lead to exclusion, but be taken into account in the overall weighing of costs and benefits of receiving the evidence. [ 50 ] As discussed in the English case law, the decision as to whether an expert should be permitted to give evidence despite having an interest or connection with the litigation is a matter of fact and degree. The concept of apparent bias is not relevant to the question of whether or not an expert witness will be unable or unwilling to fulfill its primary duty to the court. When looking at an expert’s interest or relationship with a party, the question is not whether a reasonable observer would think that the expert is not independent. The question is whether the relationship or interest results in the expert being unable or unwilling to carry out his or her primary duty to the court to provide fair, non-partisan and objective assistance. [ 51 ] Having established the analytical framework, described the expert’s duty and determined that compliance with this duty goes to admissibility and not simply to weight, I turn now to where this duty fits into the analytical framework for admission of expert opinion evidence. F. Situating the Analysis in the Mohan Framework (1) The Threshold Inquiry [ 52 ] Courts have addressed independence and impartiality at various points of the admissibility test. Almost every branch of the Mohan framework has been adapted to incorporate bias concerns one way or another: the proper qualifications component (see, e.g., Bank of Montreal ; Dean Construction ; Agribrands Purina Canada Inc. v. Kasamekas , 2010 ONSC 166 ; R. v. Demetrius , 2009 22797 (Ont. S.C.J.)); the necessity component (see, e.g., Docherty ; Alfano ); and during the discretionary cost-benefit analysis (see, e.g., United City Properties ; Abbey (ONCA)). On other occasions, courts have found it to be a stand-alone requirement: see, e.g., Docherty ; International Hi-Tech Industries Inc. v. FANUC Robotics Canada Ltd. , 2006 BCSC 2011 ; Casurina Ltd. Partnership v. Rio Algom Ltd. (2002), 2002 9356 (ON SC) , 28 B.L.R. (3d) 44 (Ont. S.C.J.); Prairie Well Servicing Ltd. v. Tundra Oil and Gas Ltd. , 2000 MBQB 52 , 146 Man. R. (2d) 284. Some clarification of this point will therefore be useful. [ 53 ] In my opinion, concerns related to the expert’s duty to the court and his or her willingness and capacity to comply with it are best addressed initially in the “qualified expert” element of the Mohan framework: S. C. Hill, D. M. Tanovich and L. P. Strezos, McWilliams’ Canadian Criminal Evidence (5th ed. (loose-leaf)), at 12:30.20.50; see also Deemar v. College of Veterinarians of Ontario , 2008 ONCA 600 , 92 O.R. (3d) 97, at para. 21 ; Lederman, Bryant and Fuerst, at pp. 826-27; Halsbury’s Laws of Canada: Evidence , at para. HEV-152 “Partiality”; The Canadian Encyclopedic Digest (Ont. 4th ed. (loose-leaf)), vol. 24, Title 62 ― Evidence, at §469. A proposed expert witness who is unable or unwilling to fulfill this duty to the court is not properly qualified to perform the role of an expert. Situating this concern in the “properly qualified expert” ensures that the courts will focus expressly on the important risks associated with biased experts: Hill, Tanovich and Strezos, at 12:30.20.50; Paciocco, “Jukebox”, at p. 595. (2) The Gatekeeping Exclusionary Discretion [ 54 ] Finding that expert evidence meets the basic threshold does not end the inquiry. Consistent with the structure of the analysis developed following Mohan which I have discussed earlier, the judge must still take concerns about the expert’s independence and impartiality into account in weighing the evidence at the gatekeeping stage. At this point, relevance, necessity, reliability and absence of bias can helpfully be seen as part of a sliding scale where a basic level must first be achieved in order to meet the admissibility threshold and thereafter continue to play a role in weighing the overall competing considerations in admitting the evidence. At the end of the day, the judge must be satisfied that the potential helpfulness of the evidence is not outweighed by the risk of the dangers materializing that are associated with expert evidence. G. Expert Evidence and Summary Judgment [ 55 ] I must say a brief word about the procedural context in which this case originates — a summary judgment motion. (I note that these comments relate to the summary judgment regime under the Nova Scotia rules and that different considerations may arise under different rules.) It is common ground that the court hearing the motion can consider only admissible evidence. However, under the Nova Scotia jurisprudence, which is not questioned on this appeal, it is not the role of a judge hearing a summary judgment motion in Nova Scotia to weigh the evidence, draw reasonable inferences from evidence or settle matters of credibility: Coady v. Burton Canada Co. , 2013 NSCA 95 , 333 N.S.R. (2d) 348, at paras. 42-44 , 87 and 98; Fougere v. Blunden Construction Ltd. , 2014 NSCA 52 , 345 N.S.R. (2d) 385, at paras. 6 and 12 . Taking these two principles together, the result in my view is this. A motions judge hearing a summary judgment application under the Nova Scotia rules must be satisfied that proposed expert evidence meets the threshold requirements for admissibility at the first step of the analysis, but should generally not engage in the second step cost-benefit analysis. That cost-benefit analysis, in anything other than the most obvious cases of inadmissibility, inevitably involves assigning weight — or at least potential weight — to the evidence. H. Application [ 56 ] I turn to the application of these principles to the facts of the case. In my respectful view, the record amply sustains the result reached by the majority of the Court of Appeal that Ms. MacMillan’s evidence was admissible on the summary judgment application. Of course, the framework which I have set out in these reasons was not available to either the motions judge or to the Court of Appeal. [ 57 ] There was no finding by the motions judge that Ms. MacMillan was in fact biased or not impartial or that she was acting as an advocate for the shareholders: C.A. reasons, at para. 122. On the contrary, she specifically recognized that she was aware of the standards and requirements that experts be independent. She was aware of the precise guidelines in the accounting industry concerning accountants acting as expert witnesses. She testified that she owed an ultimate duty to the court in testifying as an expert witness: A.R., vol. III, at pp. 75-76; C.A. reasons, at para. 134. To the extent that the motions judge was concerned about the “appearance” of impartiality, this factor plays no part in the test for admissibility, as I have explained earlier. [ 58 ] The auditors’ claim that Ms. MacMillan lacks objectivity rests on two main points which I will address in turn. [ 59 ] First, the auditors say that the earlier work done for the shareholders by the Kentville office of Grant Thornton “served as a catalyst and foundation for the claim of negligence” against the auditors and that this “precluded [Grant Thornton] from acting as ‘independent’ experts in this case”: A.F., at paras. 17 and 19. Ms. MacMillan, the auditors submit, was in an “irreconcilable conflict of interest, in that she would inevitably have to opine on, and choose between, the actions taken and standard of care exercised by her own partners at Grant Thornton” and those of the auditors: A.F., at para. 21. This first submission, however, must be rejected. [ 60 ] The fact that one professional firm discovers what it thinks is or may be professional negligence does not, on its own, disqualify it from offering that opinion as an expert witness. Provided that the initial work is done independently and impartially and the person put forward as an expert understands and is able to comply with the duty to provide fair, objective and non-partisan assistance to the court, the expert meets the threshold qualification in that regard. There is no suggestion here that Grant Thornton was hired to take a position dictated to it by the shareholders or that there was anything more than a speculative possibility of Grant Thornton incurring liability to them if the firm’s opinion was not ultimately accepted by the court. There was no finding that Ms. MacMillan was, in fact, biased or not impartial, or that she was acting as an advocate for the shareholders. The auditors’ submission that she somehow “admitted” on her cross-examination that she was in an “irreconcilable conflict” is not borne out by a fair reading of her evidence in context: A.R., vol. III, at pp. 139-45. On the contrary, her evidence was clear that she understood her role as an expert and her duty to the court: ibid. , at pp. 75-76. [ 61 ] The auditors’ second main point was that Ms. MacMillan was not independent because she had “incorporated” some of the work done by the Kentville office of her firm. This contention is also ill founded. To begin, I do not accept that an expert lacks the threshold qualification in relation to the duty to give fair, objective and non-partisan evidence simply because the expert relies on the work of other professionals in reaching his or her own opinion. Moreover, as Beveridge J.A. concluded, what was “incorporated” was essentially an exercise in arithmetic that had nothing to do with any accounting opinion expressed by the Kentville office: C.A. reasons, at paras. 146-49. [ 62 ] There was no basis disclosed in this record to find that Ms. MacMillan’s evidence should be excluded because she was not able and willing to provide the court with fair, objective and non-partisan evidence. I agree with the majority of the Court of Appeal who concluded that the motions judge committed a palpable and overriding error in determining that Ms. MacMillan was in a conflict of interest that prevented her from giving impartial and objective evidence: paras. 136-50. IV. Disposition [ 63 ] I would dismiss the appeal with costs. Appeal dismissed with costs. Solicitors for the appellants: Stikeman Elliott, Toronto. Solicitors for the respondents: Lenczner Slaght Royce Smith Griffin, Toronto; Groupe Murphy Group, Moncton. Solicitor for the intervener the Attorney General of Canada: Attorney General of Canada, Toronto. Solicitors for the intervener the Criminal Lawyers’ Association (Ontario): Henein Hutchison, Toronto.