Although the decision of the SCC was not unanimous (two of the seven judges "dissented", meaning they reached a different conclusion), that's not a problem, per se, from a legal point of view. There's very little point in appearing in (any) court and arguing for whatever a minority of the SCC had to say in any given case; the majority decision will carry the day.
But what I found interesting is the minority's analysis of the meaning (and effect) of the majority's decision.
The minority judges correctly noted that s. 16(2) provides that, if the challenged witness is able to communicate the evidence and understands the nature of an oath or a solemn declaration in terms of ordinary, everyday social conduct, he or she can testify (as a typical witness) under oath or solemn affirmation. However, if the challenged witness is able to communicate the evidence but does not understand the nature of an oath or a solemn affirmation, s. 16(3) provides that he or she may provide unsworn testimony on promising to tell the truth. But if the challenged witness does not satisfy either criteria, s. 16(4) provides they cannot testify.
Although the minority agreed with the majority that promising is an act aimed at bringing home to the witness the seriousness of the situation and the importance of being careful and correct, they disagreed with the proposition that a trial judge is not allowed to try to determine — in concrete everyday terms — whether, in reality, this actually occurs in the case of a particular witness whose mental capacity has been challenged. They reasoned that if such a witness was so disabled as not to understand the seriousness of the situation and the importance of being careful and correct, the fair trial interests of the accused are unfairly prejudiced.
In 2005, the following provisions were added to the Canada Evidence Act with respect to child witnesses.
16.1 (1) A person under fourteen years of age is presumed to have the capacity to testify.You will note that s. 16.1(7) prohibits asking a child witnesses “any questions regarding their understanding of the nature of the promise to tell the truth”. As the minority pointed out, the empirical evidence before Parliament when this amendment was made related exclusively to children; no such studies were carried out with respect to adults with mental disabilities. A “don’t ask” provision was neither proposed nor adopted with respect to adults with intellectual disabilities. In other words, as in so many other areas of criminal law, this population simply wasn't considered.
No oath or solemn affirmation
(2) A proposed witness under fourteen years of age shall not take an oath or make a solemn affirmation despite a provision of any Act that requires an oath or a solemn affirmation.
Evidence shall be received
(3) The evidence of a proposed witness under fourteen years of age shall be received if they are able to understand and respond to questions.
Burden as to capacity of witness
(4) A party who challenges the capacity of a proposed witness under fourteen years of age has the burden of satisfying the court that there is an issue as to the capacity of the proposed witness to understand and respond to questions.
(5) If the court is satisfied that there is an issue as to the capacity of a proposed witness under fourteen years of age to understand and respond to questions, it shall, before permitting them to give evidence, conduct an inquiry to determine whether they are able to understand and respond to questions.
Promise to tell truth
(6) The court shall, before permitting a proposed witness under fourteen years of age to give evidence, require them to promise to tell the truth.
Understanding of promise
(7) No proposed witness under fourteen years of age shall be asked any questions regarding their understanding of the nature of the promise to tell the truth for the purpose of determining whether their evidence shall be received by the court.
(8) For greater certainty, if the evidence of a witness under fourteen years of age is received by the court, it shall have the same effect as if it were taken under oath.
The minority agreed with the majority that the words “on promising to tell the truth” in s. 16(3) had the same meaning as “to promise to tell the truth” in s. 16.1(6). But that being the case, the minority believed that the majority must have read the s. 16.1(7) “don’t ask” rule [applicable only to children) into s. 16(3) [applicable only to mentally challenged adults] in order to read down the words “promising to tell the truth” in s. 16(3), and thus treated adults with mental disabilities as equivalent to children without mental disabilities.
The minority went on to find that just because psychiatrists speak of persons with mental disabilities in terms of mental ages does not mean that an adult with mental age of six is on the same footing as a six‑year‑old child with no mental disability whatsoever as a six‑year‑old with the mental capacity of a six‑year‑old does not suffer from a mental disability. No evidence had been provided to the court to suggest this equivalence and a court can only take "judicial notice" of alleged “facts” that are either notorious or easily verifiable from undisputed sources.
I find this analysis particularly interesting because one of the points made in an analysis of this decision by Laurie Letheren, a staff lawyer at the ARCH Disability Law Centre, is how inappropriate it was that throughout the history of R. v. D.A.I. the witness and other adults with intellectual disabilities were compared to children. She uses the example of the court accepting, without question, the evidence of the psychiatrist (who never even met the witness) that she “possessed the mental age of a three- to six-year-old”.
To me, this is wrong at so many levels, but Ms. Letherin comments on its inappropriateness, given that the young woman in question had attended high school, was involved in her community and had 19 years of lived experience, noting that such characterization of adults with intellectual disabilities needs to be challenged if the criminal justice system is to be truly inclusive.
I can certainly agree with Ms. Letherin that the 19-year-old witness could not, mentally, be the same as a three to six-year-old because she had had the life experiences of a 19-year-old, not a six-year-old; no matter the mental level those experiences had been processed at.
However, it strikes me that if we choose to look at this case through that lens, we can't ignore what is essentially the same issue (in a slightly different context) as that pointed out in the minority decision.