To Tell the Truth: R. v. D.A.I. and Witness Competency Issues

As Tony Montana in Scarface, Al Pacino delivers one of the most memorable lines in the movie: “I always tell the truth. Even when I lie.” This concern is lodged at the centre of the recent Supreme Court of Canada decision in R. v. D.A.I., 2012 SCC 5. Specifically, the Court tackled the question of what it means for a mentally disabled adult to promise to tell the truth: is it similar to a performative utterance, whereby the mere repetition of an oath, solemn affirmation or promise is sufficient to render a witness competent? Or does a witness have to engage with the meaning of truth, morality, God, etc. in a more abstract way? Ultimately, the majority of the Court, led by Chief Justice McLachlin, decided that s.16(3) of the Canada Evidence Act (“CEA”) does not necessitate an inquiry into the witness’s ability to understand abstract terms, such as truth. In so doing, the Court brings the test for competence for adults much closer to that for children under the age of 14 (s. 16.1 of the CEA). As the dissenting justices wondered out loud in their dissent, at what cost was this harmonization – between the statute that governs adults and the recently reformed legislation for children – accomplished?


This case is about sexual assault. To underline the gravity of the case, Chief Justice McLachlin begins her opinion with the statement: “Sexual assault is an evil.” Chief Justice McLachlin, throughout her opinion, laments that sexual assault cases usually involve vulnerable persons, namely children and those who are mentally impaired. K.B., the victim in this case, is a 26-year old woman who is mentally impaired. She has the mental age of a three- to six-years old, according to psychiatrists. K.B. alleges that she was repeatedly assaulted by D.A.I., the former partner of her mother. The prosecution sought to call the young woman to testify about the alleged assaults before the court. They also sought to adduce evidence through her schoolteacher and a police officer of what the victim told them.

Statutory framework

The trial judge, however, found the victim to be incompetent to testify in a court of law. Section 16 of the Canada Evidence Act governs the capacity of witnesses to testify:

16. (1) If a proposed witness is a person of fourteen years of age or older whose mental capacity is challenged, the court shall, before permitting the person to give evidence, conduct an inquiry to determine
(a) whether the person understands the nature of an oath or a solemn affirmation; and
(b) whether the person is able to communicate the evidence.

(2) A person referred to in subsection (1) who understands the nature of an oath or a solemn affirmation and is able to communicate the evidence shall testify under oath or solemn affirmation.

(3) A person referred to in subsection (1) who does not understand the nature of an oath or a solemn affirmation but is able to communicate the evidence may, notwithstanding any provision of any Act requiring an oath or a solemn affirmation, testify on promising to tell the truth.

(4) A person referred to in subsection (1) who neither understands the nature of an oath or a solemn affirmation nor is able to communicate the evidence shall not testify.

The trial judge, as the majority pointed out, applied the statute rather haphazardly to this case. He did not undertake any investigation as to whether K.B. had the ability to communicate evidence under s. 16(3); this investigation should have been the first step. The judge “insist[ed] instead on an understanding of the duty to speak the truth that is not prescribed by s. 16(3) [italics added]” (87). During the voir dire, the trial judge questioned K.B. on the nature of truth, religious obligations and the consequences of failing to tell the truth. Because the victim did not produce satisfactory answers to those questions, he ruled that, “she could not be allowed to promise to tell the truth and refused to allow her to testify” (85). The trial judge dismissed the prosecution’s questions to K.B. The prosecution would have asked K.B. to recount events and to distinguish between telling the truth and lying in concrete, real-life situations, as opposed to abstract terms.

Statutory interpretation

When a challenge is raised as to the capacity of an adult witness to testify in court, the judge must turn to s. 16(1) of the CEA. The line of questioning, which would take place during a voir dire, should be rather straightforward:
First, the judge must determine “whether the person understands the nature of an oath or a solemn declaration” and “whether the person is able to communicate the evidence”: s. 16(1). If these requirements are met, the witness testifies under oath or affirmation, as other witnesses do: s. 16(2). If these requirements are not met, the judge moves on to s. 16(3). Section 16(3) provides that “[a] person… who does not understand the nature of an oath or a solemn affirmation but is able to communicate the evidence may… testify on promising to tell the truth.” (21)

The defense takes the position that a mere promise to tell the truth is not enough. It needs to be supplemented, in the case of adult witnesses who cannot take an oath or affirm, by a clear demonstration that he/she understands the nature of a promise to tell the truth.

The majority of the bench dismisses this position. First, they discuss the amendment history of s. 16(3). Prior to the 1987 amendments (Bill C-15), the section demanded an assessment as to whether the witness was “sufficiently intelligent that the reception of the evidence is justified.” It was decided by the Committee on hand that this wording was too slippery and that it would open the door to abstract inquiries (29). As such, the wording was replaced by the requirement to ‘promise to tell the truth.’ Thus, the majority launches an examination into legislative intent, opining essentially that the drafters of the 1987 reforms did not intend for s. 16(3) to entail a robust investigation into the nature of the promise to tell the truth. They also provide compelling reasons based on the internal logic of s.16 as it stands today. A robust investigation into the nature of the promise to tell the truth under s. 16(3) would be rather redundant in the context of s. 16(1) (nature of an oath or solemn affirmation)..To supplement this reasoning, the court notes that the legal interpretation should begin with the plain words of s. 16(3). There is nothing in the section that states explicitly that a promise to tell the truth is not enough to determine the capacity of a witness to testify in a court of law. Even if we do not find the intent-based approach or the internal logic examination compelling, we should easily accept the literal meaning of the statute.

Judicial interpretation

Most of the case law that both sides confronted was related to child witnesses. (There is an extensive discussion of abstract terms from the case and the test that grew from the case, R. v. Kahn [2 SCR 531].) These cases have limited value because they all preceded the 2005 reforms that resulted in the creation of s 16.1, a section that deals with witnesses under the age of fourteen specifically: s. 16.1(5) states that a child need only be able to “understand and respond to questions”; and s. 16.1(2) provides that a child witness shall not take an oath or make a solemn affirmation. Furthermore, in R. v. Marquard [4 SCR 223], Justice McLachlin, as she then was, stated that the phrase ‘communicate the evidence’ “indicates more than a verbal ability” (246). By analogy, the dissenting judges argue that the phrase ‘promise to tell the truth’ should also indicate more than a verbal ability to utter those words.

Policy considerations

There are two vital, yet conflicting, policy considerations that are identified by the majority of the bench. Chief Justice McLachlin signals the first policy consideration in the opening words of the decision: “sexual assault is an evil.” Indeed, it is an evil, and one that disproportionately affects those with limited mental capacity. There exists, as a result, a pressing social need to bring to justice those who sexually abuse vulnerable people. Not only are victims like K.B. targeted more often, but it is much more difficult to include their voice in the legal process; “they lack the capacity to articulate in abstract terms the difference between truth and a lie and the nature of the obligation imposed by promising to tell the truth” (66). Given their precarious position and the stigma surrounding these crimes, a reading of s. 16(3) in this way may make it impossible to bring justice to these victims, according to the majority. The harms to the individual, her family and her friends do not stop there. But, it may not be necessary to amplify this point any further.

A conflicting policy consideration takes the perspective of the accused – particularly, his right to a fair trial. The common law of evidence has erected numerous safeguards that offer ample protection against the risk of wrongful conviction. Reliability is the minimal threshold that must be met before submitting evidence before a judge or jury. Evidence is, at best, reliable – not guaranteed to be truthful. Even a person with average or above-average mental abilities may be untruthful on the stand; she either lies or has forgotten or mistaken certain pieces of information. What the trial process seeks is a basic indication of reliability. After that point, the witness’s evidence can be tested by cross-examination. While on the stand, the trier of fact can assess the demeanor of a witness. Together, the trier of fact can determine whether or not to accept all, part or none of her testimony and, above all, determine the weight to accord to her evidence.


There is certainly a trend in the law of evidence in Canada that would prefer to admit more evidence at the early stages, thereby placing more emphasis on the weighing of evidence. As cases like Kahn have warned us, cases involving children and adults with limited mental capacity struggle to make it to court for a myriad of reasons. By placing high demands on these vulnerable groups, we continue to leave them on the fringes of society, and of the legal system.

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