Competence of Witnesses to Testify
Competence refers to the ability of a person to give testimony in an reliable and truthful manner. This is specifically means the witness has:
- the capacity to observe (including interpretation);
- the capacity to recollect; and
- the capacity to communicate.
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. Where competency is challenged, it must be established by a voir dire before the witness can be sworn.
Competency also includes the ability distinguish between actual memory based on observation and imagination or second hand information.
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.
A witness is barred by foreign law to testify is still competent.
Competence vs Fitness to Stand Trial
A lack of testimonial competence does not necessarily render a person unfit to stand trial.
- R v Marquard, 1993 CanLII 37 (SCC),  4 SCR 223
- R v Ferguson, 1996 CanLII 8409 (BC CA), (1996) 112 CCC (3d) 342 (BCCA)
- R v Steinberg, 1931 CanLII 4 (SCC),  SCR 421
- R v Farley, 1995 CanLII 3501 (ON CA)
- R v Walsh, (1978) 48 CCC (2d) 199 (ONCA) (*no link)
- R v Spencer 1985 CanLII 4 (SCC),  2 SCR 278
- R v Morrissey, 2007 ONCA 770 (CanLII) per Blair J. leave to SCC refused
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. It is not sufficient to merely allege that the witness has "material evidence" to provide. The calling party must prove this claim.
No party should be permitted to call a witness in order to engage in a "fishing expedition".
R v Fazekas, 2010 ONSC 6571 (CanLII) at para 11
Fazekas, ibid. at para 11
R v Elliott, CanLII 24447 (ON CA),  O.J. No. 4694, 181 C.C.C. (3d) 118 (Ont CA) at para. 119
Fazekas, ibid. at para 11
R v Harris (1994), 1994 CanLII 2986 (ON CA), 93 C.C.C. (3d) 478 (Ont. C.A.)
Competence of Accused
An accused person is not competent to be called as a witness by the crown due to s.11(c).
A person is not rendered incompetent to testify only for the "reason of interest or crime".
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.
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.
- 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;"
- see s. 3 of Canada Evidence Act
- R v McKee  O.J. No. 22, 126 CCC 251 (Ont. C.A.)
- Amway Corp.,  1 SCR 21, 1989 CanLII 107 (SCC)