CROSS EXAMINATION - IMPORTANCE OF
R. v. Lyttle, 2004 SCC 5,  1 SCR 193 CanLII
41 As mentioned at the outset, the right of an accused to cross-examine prosecution witnesses without significant and unwarranted constraint is an essential component of the right to make a full answer and defence. See R. v. Seaboyer, 1991 CanLII 76 (S.C.C.),  2 S.C.R. 577, at p. 608, per McLachlin J. (as she then was):
The right of the innocent not to be convicted is dependent on the right to present full answer and defence. This, in turn, depends on being able to call the evidence necessary to establish a defence and to challenge the evidence called by the prosecution. . . . In short, the denial of the right to call and challenge evidence is tantamount to the denial of the right to rely on a defence to which the law says one is entitled. [Emphasis added.]
42 In R. v. Osolin, 1993 CanLII 54 (S.C.C.),  4 S.C.R. 595, Cory J. reviewed the relevant authorities and, at p. 663, explained why cross-examination plays such an important role in the adversarial process, particularly, though of course not exclusively, in the context of a criminal trial:
There can be no question of the importance of cross-examination. It is of essential importance in determining whether a witness is credible. Even with the most honest witness cross-examination can provide the means to explore the frailties of the testimony. For example, it can demonstrate a witness’s weakness of sight or hearing. It can establish that the existing weather conditions may have limited the ability of a witness to observe, or that medication taken by the witness would have distorted vision or hearing. Its importance cannot be denied. It is the ultimate means of demonstrating truth and of testing veracity. Cross-examination must be permitted so that an accused can make full answer and defence. The opportunity to cross-examine witnesses is fundamental to providing a fair trial to an accused. This is an old and well-established principle that is closely linked to the presumption of innocence. See R. v. Anderson (1938), 70 C.C.C. 275 (Man. C.A.); R. v. Rewniak (1949), 93 C.C.C. 142 (Man. C.A.); Abel v. The Queen (1955), 115 C.C.C. 119 (Que. Q.B.); R. v. Lindlau (1978), 40 C.C.C. (2d) 47 (Ont. C.A.).
43 Commensurate with its importance, the right to cross-examine is now recognized as being protected by ss. 7 and 11(d) of the Canadian Charter of Rights and Freedoms. See Osolin, supra, at p. 665.
44 The right of cross-examination must therefore be jealously protected and broadly construed. But it must not be abused. Counsel are bound by the rules of relevancy and barred from resorting to harassment, misrepresentation, repetitiousness or, more generally, from putting questions whose prejudicial effect outweighs their probative value. See R. v. Meddoui, 1991 CanLII 42 (S.C.C.),  3 S.C.R. 320; R. v. Logiacco reflex, (1984), 11 C.C.C. (3d) 374 (Ont. C.A.); R. v. McLaughlin (1974), 15 C.C.C. (2d) 562 (Ont. C.A.); Osolin, supra.
45 Just as the right of cross-examination itself is not absolute, so too are its limitations. Trial judges enjoy, in this as in other aspects of the conduct of a trial, a broad discretion to ensure fairness and to see that justice is done — and seen to be done. In the exercise of that discretion, they may sometimes think it right to relax the rules of relevancy somewhat, or to tolerate a degree of repetition that would in other circumstances be unacceptable. See United Nurses of Alberta v. Alberta (Attorney General), 1992 CanLII 99 (S.C.C.),  1 S.C.R. 901, at p. 925.
46 This appeal concerns the constraint on cross-examination arising from the ethical and legal duties of counsel when they allude in their questions to disputed and unproven facts. Is a good faith basis sufficient or is counsel bound, as the trial judge held in this case, to provide an evidentiary foundation for the assertion?
47 Unlike the trial judge, and with respect, we believe that a question can be put to a witness in cross-examination regarding matters that need not be proved independently, provided that counsel has a good faith basis for putting the question. It is not uncommon for counsel to believe what is in fact true, without being able to prove it otherwise than by cross-examination; nor is it uncommon for reticent witnesses to concede suggested facts — in the mistaken belief that they are already known to the cross-examiner and will therefore, in any event, emerge....