All questions must be relevant to the proceedings. Two reasons are normally put forward for this. First, irrelevant information confuses the issues and can lead to a wrong decision by a judge or a jury. Second, irrelevant information wastes judicial resources (that is, time). Good judges keep a careful watch on relevance, both because admitting relevant information can destroy a fair trial, and because trials will take much longer if every witness gets to say everything he or she thinks about the matter. For example, if a murder victim’s sister is called to the witness stand by the prosecutor to testify that she saw her brother alive at 5 p.m. on October 31, that is all she should be allowed to testify about. Naturally, she would like to testify about what a great person her brother was, and how he would never have tried to kill Mr. Defendant at 6 p.m. on October 31, but none of that is relevant. Thus, relevance is defined by the purpose for which a witness is called to testify. While a witness may be called for more than one purpose, the lawyer must have a defined purpose for each evidentiary area and be prepared to articulate it.
In all trials, certain information comes into evidence that is not strictly relevant, but serves to lay the background for certain matters. If the information does not damage either side’s case, and is delivered relatively quickly, it generally does not draw a relevance objection. Even if it does, judges will often allow undamaging background information provided it is not to lengthy. For example, if witness X plans to testify that his store was robbed and identify the defendant as the robber, his testimony may begin with information such as (1) the name of his restaurant; (2) how many employees he has; (3) what sort of food he serves; (4) what particular tasks he was doing for the hour proceeding the robbery, and similar details that place his other testimony in a context. None of that information is strictly relevant, yet is normally allowed as long as the restaurant owner does not go on for too long or delve into a boring level of detail about it.
The definition of relevance is normally stated as “evidence which has at least some tendency to make a fact at issue more or less true”. It is not defined by the strength of the evidence, but by its character. For example, if a witness testifies he saw the defendant steal a car, but that witness was standing three hundred yards away, had terrible vision, was highly intoxicated, and has falsely testified in court many times before, his testimony is still relevant. The character of such evidence is that it is eyewitness testimony about a fact at issue – which is always relevant. Its strength is rather low, but that is for the lawyers to argue about in closing argument. Thus, a good way to think about arguing relevance in court is to be prepared to succinctly tell the court (1) what fact at issue you are trying to bolster or weaken with your question, and (2) how the offered testimony makes that fact more or less likely. An important thing to remember is that relevance is not defined by what a judge or a lawyer thinks is persuasive as to the existence or non-existence of a fact, but by whether it has any tendency to make that fact more or less true.