Decision-makers are frequently tasked with assessing witness testimony and making findings on the reliability and credibility of the witnesses before them. But is it in an error of law when a decision-maker makes findings based on their own assumptions about human behaviour and not strictly on the evidence before them?
This issue was before the Supreme Court of Canada in R v Kruk, 2024 SCC 7 [Kruk], wherein the Court declined to recognize the proposed "rule against ungrounded common sense assumptions". At issue were the findings of the Trial Judge in two separate decisions that were purportedly injected with the respective decision-maker's common sense assumptions about human behaviour within the context of sexual assault convictions. For example, one such "assumption" made by the Trial Judge was that the accused's rapid departure after the impugned event was consistent with a sexual assault having occurred.
The appellate court in each decision overturned the convictions due to the Trial Judge's impermissible reliance on their common sense assumptions regarding human behaviour that were not grounded in the evidence presented at trial. The proposed rule against ungrounded common sense assumptions directed that it was an error of law for the Judges to have integrated such assumptions in their reliability and credibility assessments.
The Supreme Court of Canada allowed the appeals, finding that no errors were made in the Trial Judges' credibility and reliability findings. Further, the Court declined to recognize the rule against ungrounded common sense assumptions for the following reasons:
1. The proposed rule improperly attempted to extend the prohibition against myths and stereotypes about sexual assault complainants. Justice Martin, writing for the majority of the Court, explained that the prohibition against myths and stereotypes about sexual assault complainants is based on a specific historical context and is designed to protect complainants. To conflate this rule to include a rule against ungrounded common sense assumptions would cast too wide of a net by improperly catching all types of factual generalizations and turning them into errors or law.
2. The proposed rule is not necessary to protect the rights of the accused, as there are several legal protections (such as the presumption of innocence and the standard of reasonable doubt) that are afforded to the accused to ensure they are treated fairly.
3. The proposed rule is incompatible with established law relating to an appellate court's review of credibility and reliability findings. To accept and impose such a rule would subject the decision-maker's findings to an overly invasive appellate review.
Justice Martin explained that common sense assumptions underly all credibility and reliability assessments and it is expected of the decision-maker to apply common sense based on their accumulation of knowledge about human behaviour to assess witness testimony. An appellate court's review of credibility and reliability findings should therefore remain subject to deference unless a palpable and overriding error can be shown or there is a recognized error of law.
While the decision in Kruk related specifically to testimony underlying criminal convictions, the Court's holding clarified the standard of review and role of appellate intervention for credibility and reliability findings in other contexts.
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