Define: Opinion Rule

The opinion rule in evidence law states that witnesses should only provide testimony on facts they have personally observed, rather than their personal opinions. This is because opinions can be subjective and lack factual basis. However, if a witness’s opinion is derived from their observations and can assist in determining the facts, it may be admissible as evidence. While some argue that this rule is outdated and disregards valuable testimony, it remains a crucial component of the legal system.

The principle that a witness should provide factual testimony rather than opinions, and that nonexpert witnesses’ opinions are often not considered as evidence, is a fundamental rule in evidence law. This principle is rooted in the belief that witnesses who have firsthand knowledge should present the most objective evidence possible, allowing the jury to draw their own conclusions from the facts. Consequently, the witness’s opinion becomes unnecessary. However, in modern times, opinions may be admissible if they are based on the witness’s perceptions and are helpful to the fact-finder. For instance, in a car accident case, a witness can testify to seeing a car run a red light and collide with another vehicle, which is a factual observation. On the other hand, if the witness states that the driver who ran the red light was reckless, this would be considered an opinion and may not be allowed as evidence. This example exemplifies the opinion rule, as the witness is expressing an opinion about the driver’s behaviour, which they did not directly observe. The jury can form their own conclusions about the driver’s conduct based on the presented facts. In a murder trial, a medical examiner, who possesses expertise in the field, can provide an opinion on the cause of death based on their examination of the body. Although this is an opinion, it is considered admissible as it is founded on the examiner’s specialized knowledge and assists the fact-finder. This example demonstrates that opinions can be accepted as evidence if they are supported by the witness’s expertise and are beneficial to determining the facts. The medical examiner’s opinion regarding the cause of death holds significant weight in the case.

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This glossary post was last updated: 17th April 2024.