What is the test for determining whether a document is relevant or material?

Slatter J., as he then was, considered the concepts of “relevant” and “material” in Weatherill Estate v. Weatherill 2003 ABQB 69: In determining whether a document is relevant and material, the starting point is the pleadings. The pleadings define the issues, and relevance must be determined with respect to the issues. The pleadings are also relevant with respect to the issue of materiality. However, with respect to materiality one must also have regard to the issue in question. Where does the burden of proof lie? Is the issue something that is capable of direct proof, or is it something like a person’s state of mind, which can only be proven indirectly? Does one party essentially have to try and prove a negative? How are cases of this type usually proven at trial? The less amenable a fact is to direct proof, the wider will be the circle of materiality. There are some facts that can only be proven by essentially eliminating all the competing scenarios, thereby leaving the fact in issue as the sole logical inference.... in deciding whether a particular document is material, one must take a very pragmatic view, viewing the situation from the perspective of the party who must prove the fact in question. At an interlocutory stage of proceedings, the court should not measure counsel’s proposed line of argument too finely; if counsel can disclose a rational strategy in which the disputed document plays a material part, that should be sufficient. Again it must be remembered that the purpose of the rule was to avoid abusive, excessive, and unnecessarily expensive discovery, not to cut off legitimate lines of inquiry.