Evidence of a witness’s religious beliefs is not admissible for the purposes of enhancing or impeaching his or her credibility, nor can it be relied upon for those purposes.


In R. v. Santhosh, 2016 ONCA 731 (CanLII), the Court of Appeal for Ontario set out three reasons for this rule.
1. Not Probative
Evidence of a witness’s religious beliefs is simply not useful in assessing credibility.

In considering evidence potentially relevant to credibility the court must first ask whether the evidence indicates the witness is more or less likely to tell the truth in court. The tendency or disposition of a person to do a certain act is relevant to indicated the probability of his doing or not doing the act. 

In order for character evidence to be relevant to credibility, it must establish a tendency or dispositionto tell the truth or to lie. The bare fact of membership in a faith group does nothing to establish such a tendency or disposition. There are people of all religious beliefs – and of no religious beliefs – who lie, just as there are those who are truthful.
2. Risk of Moral and Reasoning Prejudice
Relatedly, the risk of prejudice associated with using evidence of a witness’ religious beliefs for credibility purposes is extremely high, far outstripping any possible probative value. There is a risk of both moral and reasoning prejudice.
[These concepts were described in R. v. Handy, 2002 SCC 56 (CanLII) at paras. 139-147; see also R. v. Pollock (2004), 187 C.C.C (3d) 212 (Ont. C.A.) at paras. 99-111]. 
Evidence of a witness’ religious beliefs may distract the trier of fact from the core issues and lead them to draw improper inferences based on prejudice or stereotyping. This is particularly true in cases where a witness holds minority religious views that are poorly understood, or even disliked, by the majority in society. Of course, the converse is also of serious concern: there is a risk that the witness who holds more mainstream, popularly understood beliefs is more likely to be held credible. 
The courts must be especially vigilant to excise from consideration factors that may lead to unconscious prejudice.
3.  Contrary to Public Policy
Public policy concerns militate against using evidence of a witness’ religious beliefs for credibility purposes. The Charter values of freedom of conscience and religion and of equality would be undermined by permitting or encouraging inquiry into the religious beliefs of witnesses in our courts for the purposes of assessing credibility. 
[While there are some very limited circumstances in which inquiry into the degree to which an oath or affirmation binds a witness’ conscience is permissible, these are restricted to where there is reason to believe that the witness’ oath or affirmation is not genuine. Such an inquiry is primarily a question of testimonial competence as opposed to credibility].