opinion rule.Evidence. The principle that a witness should testify to facts, not opinions, and that a nonexpert witness’s opinions are often excludable from evidence. • Traditionally, this principle is regarded as one of the important exclusionary rules in evidence law. It is based on the idea that a witness who has observed data should provide the most factual evidence possible, leaving the jury to draw inferences and conclusions from the evidence. Under this system, the witness’s opinion is unnecessary. Today, opinions are admissible if rationally based on a witness’s perceptions and helpful to the fact-finder. [Cases: Criminal Law  448; Evidence  471, 505. C.J.S.

Criminal Law § 1050; Evidence §§ 509–512, 518–519, 528–529, 533, 535–537, 542, 556,

558–562, 582, 588–590, 592–593, 596–597, 609; Executions § 435.]

“This rule [the opinion rule] is an historical blunder, for the early cases excluding ‘opinion’ meant a belief by a person who had personally seen and known nothing, and was therefore not qualified to speak; whereas the modern rule applies it to witnesses who have had personal observation as a basis for their inference. Moreover, it is a senseless rule, for not once in a thousand times can the observed data be exactly and fully reproduced in words. Still further, no harm could be done by letting the witness offer his inference, except perhaps the waste of a moment’s time, whereas the application of the rule wastes vastly more time. And finally the rule is so pedantically applied by most courts that it excludes the most valuable testimony, such as would be used in all affairs of life outside a court room.” John H. Wigmore, A Students’ Textbook of the Law of Evidence 156 (1935).

“The [opinion] rule in its stark simplicity might be interpreted as excluding all value judgments, that is to say all statements not being factual propositions susceptible of some sort of empirical proof or disproof. The rule, if it is to be given any purely logical meaning at all, must be

interpreted as excluding at least all inferences drawn from perceived data. Even if value judgments are saved by construing the rule as having application only to factual propositions, the rule would seem to purport to exclude all such propositions in the formulation of which inference by the witness has played some part.” Zelman Cowen, Essays on the Law of Evidence 162 (1956).

[Blacks Law 8th]