Litigation Process a.. - The Advocates' Society

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confound the trier of fact, unduly complicate the issues, or run the risk of “mystifying” the trier of
fact to the extent that the ability to remain objective is compromised. 10
ii)
Necessity
To meet the requirement of necessity, expert evidence tendered at trial must be deemed
to be “necessary in the sense that it provides information that is likely to be outside the
experience or knowledge of a judge or jury”. 11
In R. D. (D.) 12 the Supreme Court stated that
expert evidence will be deemed necessary in those exceptional cases where the trier of fact is
unable to reach its own conclusion in the absence of assistance from experts with special
knowledge. 13 The courts have excluded expert evidence on the basis that an understanding of
concepts and principles underlying the action did not require expert assistance and where there
existed no specialized and standardized body of conduct to study in the area. 14 Moreover,
where the issue for which expert evidence is sought to be tendered amounts to an opinion on a
legal issue, the courts will not permit the expert to usurp the function of the court. 15 It is
important to bear in mind the “ultimate issue rule”. This rule stipulates that a court cannot admit
evidence which purports to answer the very question which the trier of fact must resolve for
itself. In professional liability cases, therefore, it is never appropriate to ask the expert whether
in her opinion, the defendant was negligent, as this is a finding reserved to the trier of fact.
Rather, the expert should be asked to opine as to the applicable standard of care and whether,
in the particular case, the defendant met that standard.
10 Mohan, supra at note 3, p. 21; Sopinka et. al., supra at note 6, p. 620; R v. Melangri (1992), 73 C.C.C. (3d) 348
(Ont. Gen Div.)
11 Ibid, Mohan at p. 24.
12 [2002] 2 S.C.R. 275.
13 Also see Mayfield v. Mayfield (2001), 18 R.F.L. (5 th ) 328 (Ont. Sup. Ct.) where the court concluded that where it is
not shown that expert evidence is necessary in the sense described above, it will not be admitted as expert
evidence is costly and time consuming.
14 Pente Investment Management Ltd. v. Schneider Corp., [1998] O.J. No. 6387 (Ont. Gen. Div.); the court refused to
admit evidence as to the standard to be applied to the performance of the Board of Directors.
15 Ibid.
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