Although all evidence introduced by a lawyer must be considered “relevant evidence” before it can be admitted, many lawyers today would nevertheless struggle to give an adequate legal definition of the word “relevancy”. According to the Advisory Committee’s notes in drafting Rule 401 of the Federal Rules of Evidence, the proper definition is in the form of a question, which is “whether [the] item of evidence, when tested by the processes of legal reasoning, possesses sufficient probative value to justify receiving it in evidence”. The Advisory Committee further noted that this question must be satisfied by testing whether or not the evidence would tend to make the existence of a consequential fact of the case “more or less probable”. The Committee described the standard of probability as simply anything that made the fact “more or less probable than it would be without the evidence”. The Committee went on to cite the legal authority on evidence, McCormick, who stated: “A brick is not a wall”, meaning the evidence just has to contribute in some way to the matter for which it is being introduced.
This of course led to a second problem, though, which is that of conditional relevancy. What if the evidence’s contribution of probability towards one fact is contingent on some other fact? Rule 104(b), on preliminary questions of the court, considers this to be a question for the jury to decide. A judge would pose the question to the jury as “[evidence in dispute] may only be considered if you find the existence of [this other fact] to be true”. That kind of legal charge to the jury invokes the concept which had been discussed in a previous blog on the need for foundational proof.