THE COLLATERAL FACTS RULE

Collateral matters have been defined as matters which are not determinative of an issue arising in the pleadings or indictment, or not relevant to matters which must be proved for the determination of the case. 

The general rule respecting collateral fact evidence is that one cannot impugn a witness’s credibility by contradicting the witness on matters which are collateral, even in a case where the core issue is credibility. 

As one court has put it: “Collateral evidence is evidence which depends for its relevance on the fact that it contradicts a witness.”

R. v. H. (J.),  2014 NLCA 25 (CanLII), at para 33.

The Reason for the Rule

The collateral facts rule prohibits the introduction of evidence for the sole purpose of contradicting a witness’ testimony concerning a collateral fact.  The rule seeks to avoid confusion and proliferation of issues, wasting of time and introduction of evidence of negligible assistance to the trier of fact in determining the real issues of the case.  It endeavours to ensure that the sideshow does not take over the circus.  In general, matters that relate wholly and exclusively to the credibility of a non-accused witness are collateral, hence beyond the reach of contradictory evidence.

Watt’s Manual of Criminal Evidence (Toronto: Carswell, Thomson Canada Limited, 2002), at  p. 265.

Simply—the Rule Prohibits the Leading of Extrinsic Contradictory Evidence

The collateral fact rule does not curtail what is otherwise proper cross-examination of a witness; it potentially limits the manner in which answers given may be subsequently challenged by extrinsic evidence:

As is often said, if the questioner asks a question that bears on a collateral issue, he or she is “stuck” with the answer, in the sense of not being permitted to lead extrinsic evidence to contradict it. However, this does not prevent proper questions from being put in the first place.

R. v. MacIsaac, 2017 ONCA 172, at para 58, 59.

Exceptions to the Rule

The collateral fact rule is most often engaged when a cross-examiner attempts to challenge the credibility of a witness. Credibility is generally considered to be collateral, thereby barring the questioner from adducing extrinsic evidence that bears solely on this issue. However, the rule has developed in a manner that admits of a number of exceptions.

Generally speaking, answers to questions directed solely at the impeachment of credibility must be taken as final, except:

(i)    to prove a charge of bias/partiality in favour of the opposing party;

(ii)   to prove that a witness has previously been convicted of a criminal offence(s);

(iii)  to prove that a previously inconsistent statement was made by a witness where the foundation has been laid;

(iv)  medical evidence to prove that, by reason of a physical or mental condition, the witness is incapable of telling or unlikely to tell the truth;

(v)   to prove by independent evidence that an adverse witness has a general reputation for untruthfulness and that the witness testifying to such reputation would not believe the impugned witness under oath.