3. The Ultimate Issue Rule
| Author | David M. Paciocco - Lee Stuesser |
| Profession | Justice of the Ontario Court of Justice - Professor of Law, Bond University |
| Pages | 185-190 |
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It was once said that "an opinion [whether lay or expert] can never be received when it touches the very issue before the [court]."10The concern was that to allow a witness to express her "verdict" on the very issue that the trier of fact had to decide would be "usurping the functions of the jury." Put more simply, there was fear that the trier of fact might be influenced unduly by the opinion, accepting it uncritically regardless of the actual evidence in the case. There is no longer an "ultimate issue" rule that absolutely bars qualified witnesses from offering opinions on the ultimate issues in a case. The ultimate issue rule was put to rest for lay witnesses in Graat v. R.11There the accused attempted to use the ultimate issue rule to oppose the admission of lay opinions about his impairment. He argued that impairment was the very issue before the court and that to let witnesses say that his ability to drive was impaired might cause the judge simply to accept their judgment, rather than deciding the case on the evidence. Dickson J. criticized the ultimate issue rule and said that so long as the opinions were not superfluous, they were properly heard. He remarked that witnesses cannot "usurp" the role of the trier of fact because the trier is free to accept all, or part, or none of their testimony. It is the trier of fact who renders the verdict, not the witnesses.
Even though the fear of undue influence is more compelling where the opinion witness is an "expert," it has since been resolved that the ultimate issue rule is also gone for expert witnesses; there is no rule of general application preventing expert witnesses from offering opinions
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on the ultimate issues in a case.12As will be seen later in this chapter, however, the fact that an expert is about to testify on one of the ultimate issues in the case will sometimes be a factor to consider in determining whether the testimony will be admitted.13Although the ultimate issue rule itself is gone, two of its cousins survive. The first of those rules provides that a witness cannot offer an opinion on a pure question of domestic law. The second has come to be known as the rule against oath-helping.
No witness, expert or otherwise, can provide an opinion on a pure question of domestic law. 14The rule is easy to state and to understand - evidence is to be about questions of fact, not law. The law is for lawyers to argue, not witnesses to offer. It was therefore an error for a trial judge to permit a taxpayer to call a family law lawyer to explain that a clause in a separation agreement was legally enforceable,15it was an error for the trial judge to allow an expert witness to interpret the word "appreciates" in section 16 of the Criminal Code, pertaining to the mental disorder defence,16and it was wrong for an expert to offer an opinion on whether the accused was "guilty."17Occasionally, however, a legal standard does not have its own technical definition and requires nothing more than a conclusion of fact to resolve. For example, the concept of impairment in the offence of impaired driving refers to nothing more than the fact of impairment. Because it holds the same legal meaning as the term would have for laypersons, it is not a pure question of law and there is no problem in allowing witnesses to state opinions on that ultimate issue.
It is appropriate for a court to receive expert evidence about foreign law. Foreign laws are not laws here. The content of foreign law is therefore treated as a question of fact. And since domestic judges are not trained in foreign law, they require the assistance experts in the foreign law can offer.18
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A properly qualified witness can provide general information relevant in judging the credibility of a witness, but is prevented by the rule against oath-helping from expressing an opinion about whether a particular witness is telling the truth.
"The rule against oath-helping prohibits the admission of evidence adduced solely for the purpose of proving that a witness is truthful."19
The rule exists because "[i]t is a basic tenet of our legal system that judges and juries are capable of assessing credibility and reliability of evidence."20Triers of fact can discharge their central function of deciding the ultimate issue of whether witnesses are providing accurate testimony without the need for the opinions of others about whether those witnesses are being truthful. It is not just that such opinions are superfluous or unnecessary. Even though laypeople are capable of assessing credibility, determinations of credibility are notoriously difficult. There is fear that if experts, or even laypersons familiar with witnesses,21are permitted to express their opinions as to whether witnesses are telling the truth or furnishing accurate information, triers of fact...
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