• 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.]
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.
