31.06 (1) A person examined for discovery shall answer, to the best of his or her knowledge, information and belief, any proper question relevant to any matter in issue in the action or to any matter made discoverable by subrules (2) to (4) and no question may be objected to on the ground that,
(a) the information sought is evidence;
(b) the question constitutes cross-examination, unless the question is directed solely to the credibility of the witness; or
(c) the question constitutes cross-examination on the affidavit of documents of the party being examined.
 The case law has developed the following principles about the scope of the questioning on an examination for discovery:
• The scope of the discovery is defined by the pleadings; discovery questions must be relevant to the issues as defined by the pleadings: Playfair v. Cormack (1913), 4 O.W.N. 817 (H.C.J.).
• The examining party may not go beyond the pleadings in an effort to find a claim or defence that has not been pleaded. Overbroad or speculative discovery is known colloquially as a "fishing expedition" and it is not permitted: Playfair v. Cormack, supra.
• An examination for discovery is a device of civil procedure designed to assist a party in proving his or her claim or defence. It, however, is not meant to be an instrument for a party to discover whether he or she has a claim or defence, although this sometimes occurs as a by-product of a properly conducted discovery. Overbroad or speculative discovery is not permitted:Cominco Ltd. v. Westinghouse Can. Ltd. 1979 CanLII 489 (BC CA), (1979), 11 B.C.L.R. 142 (B.C.C.A.); Allarco Broadcasting Ltd. v. Duke (1981), 26 C.P.C. 13 (B.C.S.C.).
• The extent of discovery is not unlimited, and in controlling its process and to avoid discovery from being oppressive and uncontrollable, the court may keep discovery within reasonable and efficient bounds: Graydon v. Graydon(1921), 67 D.L.R. 116 (Ont. S.C.) at pp. 118 and 119; Kay v. Posluns reflex, (1989), 71 O.R. (2d) 238 (H.C.J.) at p. 246; Ontario (Attorney General) v. Ballard Estate 1995 CanLII 3509 (ON CA), (1995), 26 O.R. (3d) 39 (C.A.) at p. 48; 671122 Ontario Ltd. v. Canadian Tire Corp.,  O.J. No. 2539 (Gen. Div.) at paras. 8-9; Caputo v. Imperial Tobacco Ltd.,  O.J. No. 2269 (S.C.J.); Andersen v. St. Jude Medical Inc.,  O.J. No. 5383 (Master).
• The deponent on an examination for discovery may be questioned for hearsay evidence because an examination for discovery requires the witness to give not only his or her knowledge but his or her information and belief about the matters in issue: Van Horn v. Verrall (1911), 3 O.W.N. 439 (H.C.J.); Rubinoff v. Newton,  1 O.R. No. 402 (H.C.J.); Kay v. Posluns, supra.
• However, a party's duty to inform himself or herself does not go so far as to require the party to inform himself about the information from third parties, strangers, or outside sources who might be witnesses in the proceeding: Star Electric Fixtures Ltd. v. Sussex Fire Insurance Co.,  O.J. No. 106 (H.C.J.) at para. 9; Concept 80 Ltd. v. W.A. Construction Co.,  O.J. No. 1503 (H.C.J.).
• The deponent on an examination for discovery may be questioned about the party's position on questions of law; Six Nations of the Grand River Indian Band v. Canada (Attorney General) reflex, (2000), 48 O.R. (3d) 377 (S.C.J.).
 Materiality and relevance are key determinants in determining the propriety of a question on an examination for discovery because a deponent may justifiably refuse to answer a question if it is not material or relevant.
 What facts are in issue, which is to say, what facts are contested or disputed, is explained by the idea of materiality. Evidence that does not address any issue arising from the pleadings or the indictment (a fact in issue) or the credibility of a witness (perception, memory, narration, or sincerity) is immaterial, and it is inadmissible: Sopkina, Lederman, Bryan, The Law of Evidence in Canada (2nd ed.), paras. 2.36, 2.50. For example, a person's mental state may be an issue in a given case. If it is an issue, then evidence that would be relevant to proving that the person was inebriated or angry or depressed would be material. If the person's mental state was not an issue in the case, then the evidence about inebriation, anger, or depression would be immaterial because it would not matter to the outcome of the case.
 To be relevant, evidence must increase or decrease the probability of the truth of the facts in issue: R. v. Morris,  2 S.C.R. No. 190; Cloutier v. The Queen,  2 S.C.R. No. 709. Relevance is about the tendency of the evidence to support inferences. In R. v. Arp,  3 S.C.R No. 339 at para. 38 the Supreme Court of Canada stated:
To be logically relevant, an item of evidence does not have to firmly establish, on any standard, the truth or falsity of a fact in issue. The evidence must simply tend to "increase or diminish the probability of the existence of the fact in issue." As a consequence, there is no minimum probative value required for evidence to be relevant.
 In R. v. Pilon,  O.J. No. 1172 (C.A.) at para. 33. Justice Doherty stated:
Evidence is relevant if, as a matter of common sense and human experience, it makes the existence of a fact in issue more or less likely? Relevance is assessed by reference to the material issues in a particular case and in the context of the entirety of the evidence and the positions of the parties.
See also R. v. Watson,  O.J. No. 2695 (C.A.).
 In class proceedings, the general rule is that the examinations for discovery are restricted to just the issues that have been certified: 1176560 Ontario Ltd. v. Great Atlantic & Pacific Co. of Canada,  O.J. No. 5703 (Master) at paras. 6 and 9; Andersen v. St. Jude Medical Inc.,  O.J. No. 3659 (Master), aff'd  O.J. No. 5769 (S.C.J.); T.L. v. Alberta (Child, Youth and Family Enhancement Act, Director), 2010 ABQB 203 (CanLII), 2010 ABQB 203 at para. 18; Abdulrahin v. Air France, 2010 ONSC 3953 (CanLII), 2010 ONSC 3953.