Competence of Witnesses to Testify

From Criminal Law Notebook
This page was last substantively updated or reviewed November 2017. (Rev. # 92263)

General Principles

See also: Competence and Compellability

Competence refers to the ability of a person to give testimony.[1] A competent witness must be able to give evidence in an reliable and truthful manner. This is specifically means the witness has:[2]

  1. the capacity to observe (including interpretation);
  2. the capacity to recollect; and
  3. the capacity to communicate.
Effect of Incompetence

A person who is not competent to testify is not permitted to testify, even if they wish to do so.[3]


The main purpose of a requirement of competency is to "exclude ... worthless testimony" on the basis that the witness lacks capacity to communicate useful evidence.[4]

Presumptions for Capacity and Incapacity

At common law, all individuals are presumed competent to testify so long as their information is relevant barring certain groups of people. Historically, the common law prevented many types of people from testifying. This included convicts, infants, the insane, marriage, and lack of belief in a higher power. Many of these rules have been overturned by statute, for example, the rule against convicts was removed under by section 12 of the Canada Evidence Act. Their record, however, can be used as character evidence.

The three classes of exceptions that remain today are children, people of low mental capacity, and spouses. In each of these, it is up to a challenger to establish the incompetence of the witness.

Standard of Proof

The proof of competency or incompetency is on the balance of probabilities.[5] Where competency is challenged, it must be established by a voir dire before the witness can be sworn.[6]


Competency also includes the ability distinguish between actual memory based on observation and imagination or second hand information.[7]


A witness who states that they may not tell the truth is still competent to testify. Such issues of truthfulness are factors of credibility for the trier-of-fact.[8]

International Law

A witness is barred by foreign law to testify is still competent.[9]

Competence vs Fitness to Stand Trial

A lack of testimonial competence does not necessarily render a person unfit to stand trial.[10]

  1. R v Nguyen, 2015 ONCA 278 (CanLII), 125 OR (3d) 321, per Gillese JA, at para 11
  2. R v Marquard, 1993 CanLII 37 (SCC), [1993] 4 SCR 223, per McLachlin J
  3. Nguyen, supra at para 11
  4. R v DAI, 2012 SCC 5 (CanLII), [2012] 1 SCR 149, per McLachlin CJ, at para 16 Nguyen, supra at para 11
  5. R v Ferguson, 1996 CanLII 8409 (BC CA), 112 CCC (3d) 342, per Finch JA
  6. R v Steinberg, 1931 CanLII 4 (SCC), [1931] SCR 421, per Anglin CJ
  7. R v Farley, 1995 CanLII 3501 (ON CA), 99 CCC (3d) 76, per Doherty JA
  8. R v Walsh, 1978 CanLII 2490 (ON CA), 48 CCC (2d) 199 (ONCA), per Martin JA
  9. R v Spencer, 1985 CanLII 4 (SCC), [1985] 2 SCR 278, per La Forest J
  10. R v Morrissey, 2007 ONCA 770 (CanLII), 227 CCC (3d) 1, per Blair JA leave to SCC refused

Material Evidence

Prove of Relevancy of Witness

The burden is upon the party calling a witness to establish that "it is probable that the witness will give material evidence on a fact in issue.[1] It is not sufficient to merely allege that the witness has "material evidence" to provide. The calling party must prove this claim.[2]

No party should be permitted to call a witness in order to engage in a "fishing expedition."[3]

  1. R v Fazekas, 2010 ONSC 6571 (CanLII), per Hennessy J, at para 11
  2. Fazekas, ibid., at para 11
    R v Elliott, 2003 CanLII 24447 (ON CA), [2003] OJ No 4694, 181 CCC (3d) 118, per curiam, at para 119
  3. Fazekas, ibid., at para 11
    R v Harris, 1994 CanLII 2986 (ON CA), 93 CCC (3d) 478, per curiam

Competence of Accused

An accused person is not competent to be called as a witness by the crown due to s.11(c).[1]

A person is not rendered incompetent to testify only for the "reason of interest or crime."[2]

A co-accused in a joint trial may be competent as a witness for the crown if they plead guilty part way through the trial.[3]

A corporate entity charged with an offence is not protected by s. 11(c). Its officers are thus competent to be called as witnesses for the Crown.[4]

  1. Section 11 of the Charter states "11. Any person charged with an offence has the right...(c) not to be compelled to be a witness in proceedings against that person in respect of the offence;"
  2. see s. 3 of Canada Evidence Act
  3. R v McKee, 1960 CanLII 509 (ON CA), [1960] OJ No 22, 126 CCC 251, per Porter CJ
  4. R v Amway Corp, 1989 CanLII 107 (SCC), [1989] 1 SCR 21, per Sopinka J

Competence of Jurors

A juror is a competent witness.[1]A juror however cannot testify to any evidence concerning the deliberations, emotions, or decisions of any of the jury panel.[2]

  1. R v Budai et al, 1999 BCCA 501 (CanLII), 140 CCC (3d) 1, per Mackenzie JA (4:1)
  2. R v Pan; R v Sawyer, 2001 SCC 42 (CanLII), [2001] 2 SCR 344, per Arbour J

Competence of Children and Witnesses of Diminished Capacity

See Also