We learned, when discussing oral evidence, that oral evidence is meant to be a description, by the witness, of things they observed using their own five senses. In reality though, humans almost never simply observe. We invariably interpret those things we have observed. Our ability to do so effectively has already been described as one of the limits on oral evidence – the limit of comprehension.
As soon as a witness begins interpreting facts rather than simply reporting them, they enter the realm of opinion evidence. In some circumstances, opinion evidence can be extremely valuable for the court. The court may not, in fact, be able to effectively understand the context of facts, unless some level of opinion is given. However, we should bear in mind at all times that the court is required, on behalf of society generally, to apply the final interpretation to facts.
Opinion evidence, then, will often be admissible when it assists the court from interpreting the facts; it will usually be inadmissible when it purports to interpret the facts on the court’s behalf.
Opinion evidence comes in two basic forms: non-expert opinion evidence, and expert opinion evidence. Non-expert opinions are opinions given by witnesses who have been called upon because they can give evidence about things they observed. These witnesses will often be allowed to stray (to a mild degree) into opinion evidence, but once the court has sufficient information to understand the context of their evidence, any further opinions will be inadmissible.
Expert opinion evidence, on the other hand, occurs when the court calls upon an expert in a field other than law, to assist the court to understand the facts before it. Sometimes, in complicated matters, the only sensible way for a court to understand those matters, is to call upon an expert in another field.
Strict rules surround the giving of expert evidence. In particular, the side calling on the expert must actually demonstrate that the witness is an expert; the witness will then be limited to answering questions only in relation to their field of expertise. Finally, no matter what the expert says, the expert’s evidence can only ever be for the guidance of the court. The court – including the jury in a jury case – is free to ignore or depart from the expert’s opinions if they are unpersuaded.
Reading:
Field Textbook, Chapter 11 (Required)
At the end of Topic 11, you should be able to:
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This unit was last updated on 28.10.2019