opinion evidence going to the issues of liability and causation
should have been excluded.
 The first problem, as I see it, is that the admissibility crite-
ria were not applied to the specific opinions it was proposed that
Dr. Smith would provide. As Doherty J.A. explained in Abbey, the
first step in determining admissibility of an expert’s opinion evi-
dence is to identify the substance and scope of an expert’s opin-
ion. He cautioned, at para. 62, that this first step is essential:
The admissibility inquiry is not conducted in a vacuum. Before deciding
admissibility, a trial judge must determine the nature and scope of the proposed
expert evidence. In doing so, the trial judge sets not only the boundaries of the
proposed expert evidence but also, if necessary, the language in which the
expert’s opinion may be proffered so as to minimize any potential harm to the
trial process. A cautious delineation of the scope of the proposed expert evidence
and strict adherence to those boundaries, if the evidence is admitted, are essential.
 In this case, the trial judge did not consider the specific
opinions to be proffered by Dr. Smith, other than the four opinions that were not contained in his reports. The Mohan/White
Burgess analysis ought to have been applied with the particular
opinions in mind, as well as their intended use.
 Turning to the specific threshold criteria, I agree with the
respondent that Dr. Smith’s evidence was not necessary to the
central liability question — whether the sexual assaults occurred.
That issue depended on an assessment of credibility. There was
no need for expert evidence to help the jury decide whether Mr.
Imeson was credible. Indeed, as I have explained, Dr. Smith’s
observations related to whether the assaults occurred, and the
connections he drew between Mr. Imeson’s conduct and the sexual
abuse, were not premised on Dr. Smith’s expertise. Rather, he readily acknowledged that his role was not to determine whether the
abuse actually occurred, and that, in his therapeutic role, he was
willing to accept what Mr. Imeson told him as the truth.
 The respondent contends that Dr. Smith’s opinion linking
Mr. Imeson’s subsequent conduct to his sexual abuse was essential evidence for the jury to consider in determining whether the
abuse he testified about had occurred. His counsel points to R. v.
Llorenz,  O.J. No. 1885, 145 C.C.C. (3d) 535 (C.A.), leave to
appeal to S.C.C. abandoned  S.C.C.A. No. 335, where this
court accepted, at para. 35, that “in some cases, expert evidence
may be admitted to show that certain behaviours, symptoms, or
psychological conditions could be consistent with sexual abuse”.
 In my view, it cannot be said that Dr. Smith’s evidence
linking Mr. Imeson’s subsequent conduct to the alleged sexual
abuse was essential to assist the jury since Dr. Smith was not