As a general rule, a party may not ask questions or present evidence solely to bolster the credibility of his own witness.
Although it may be of assistance to hear testimony about the value of the evidence that has been led in a case, there is concern that to allow this would take an undue amount of time and create distracting side issues. Until their credibility has been made an issue by the opposing party, witnesses are assumed to be trustworthy and of good character.1As a general rule, therefore, a party cannot initiate evidence solely to establish that his witnesses are credible. Evidence must be about the primarily material issues in the case, not about other evidence in the case. In R. v. Siu
this rule was contravened where a police officer stated that he believed the key Crown witness.2The rule was further breached when the officer testified that his belief was based in part on the offer of the Crown witness to take a polygraph test. Where a party leads inadmissible evidence to support the credibility of one of its witnesses in a jury trial, the trial judge should immediately direct the jury to disregard the evidence.3At the same time, it is permissible and indeed customary to introduce a witness to the court. It is common to see witnesses provide their age and describe their family and employment status and their connection to the case. Frequently, counsel will attempt to introduce their witnesses in a way that will enhance the witness’s credibility. It is a question of degree when the line is crossed between permissible introduction and impermissible "bolstering." In R. v. Clarke, for example, that line was crossed when a police informant testified that he was allowed to leave the prison for street visits, he was studying the Bible, he attended Alcoholics Anonymous, and he had reformed his criminal ways.4
 R. v. Giraldi (1975), 28 C.C.C. (2d) 248 (B.C.C.A.), leave to appeal to S.C.C. refused (1975), 28 C.C.C. (2d) 248n (S.C.C.). This is a reference to the character of the witness for truthfulness, not a reference to the accuracy or even truthfulness of what the witness is saying in the case. In other words, while witnesses are assumed to be of good character absent evidence to the contrary, it would be wrong to presume that witnesses are giving accurate testimony...