Collateral Fact Rule
A collateral fact is a "fact not directly connected" or not relevant to "the issue in dispute" The collateral fact rule prohibits the admission of any evidence that would tend to contradict any previously admitted collateral evidence. Any extrinsic contradictory evidence that brings a witnesses credibility into question may not be considered where the contradictory evidence not relevant to an issue at trial. When a witness speaks to a fact, the veracity of the testimony can only be brought into question where it is sufficiently material to a trial issue. Otherwise, it will fall up against the collateral fact rule that prohibits the calling of contradictory evidence on immaterial facts. Thus, testimony on collateral issues is conclusive. This rule has been codified in certain legislation including s. 10 and 11 of the CEA.
Collateral evidence is also characterized as evidence which derives its relevance only from the fact that it is admitted for the purpose of contradicting other evidence and nothing else.
A foundational test for collateral fact is whether the evidence contradicting the statement of the witness could be validly led as evidence on its own. Thus, statements to evidence that is not directly connected to a material fact cannot be contradicted.
The rule equally applies in cases that turn on credibility.
Exceptions to the Rule
Exceptions exists for certain evidence going to credibility:
- existence of material previous statement
- prior convictions
- honesty or history of lying
- bias or partiality
- motive to fabricate
- bad reputation
- ability to communicate.
Where a witness denies having an animus against the accused at the time of the offence may be contradicted with extrinsic evidence. However, where a witness concedes having an animus against he accused at the time of the offence, they may be cross-examined on an ongoing animus including at the time of trial. 
- R v MC, 2012 ONSC 882 (CanLII) per Thornburn J citing Black's law Dictionary
R v Prebtani, 2008 ONCA 735 (CanLII) per Rosenberg JA
R v Cargill,  2 K.B. 271 (C.C.A.)
R v Hrechuk (1950), 10 C.R. 132 (Man. C.A.)(*no link), at p. 135
R v Rafael, 1972 CanLII 640 (ON CA), (1972), 3 O.R. 238 (C.A.) at p. 330 per Arnup JA
R v Latour, 1976 CanLII 145 (SCC),  1 SCR 361, at p. 367 per De Grandpre J
R v Cassibo, 1982 CanLII 1953 (ON CA), (1982), 39 O.R. (2d) 288 (C.A.), at p 506 per Martin JA
R v JH, 2014 NLCA 25 (CanLII), at para 33
- A.G. v Hitchcock 1847, 154 ER 38 at 42
R v R(D),  2 SCR 291, 1996 CanLII 207 per Major J
- R v Aalders, 1993 CanLII 99 (SCC),  2 SCR 482 per Cory J
R v McIntosh, 1999 CanLII 1403 at para 86 per Weiler JA
R v Van Leeuwen, 2012 ONSC 132 (CanLII) per Durno J
R v Biddle,  1 SCR 761, 1995 CanLII 34 per Sopinka J
Masztalar v Wiens, 1992 CanLII 5953 (BC CA) per Cumming JA
- See R v Lindlau; however, if admitted more evidence cannot be lead
- R v P(G), 1996 CanLII 420 (ON CA), (1996), 112 CCC (3d) per Rosenberg JA
- R v Farquharson, 2002 CanLII 41775 (ON CA)