Testifying Part 5 – Non-Expert Opinion Evidence
Original article: January 17, 2017 | By Sweta Tejpal | Reviewed and updated October 7, 2026
When can a non-expert give an opinion in a criminal trial? Witnesses normally describe facts they personally perceived. Sometimes an everyday impression is a useful, practical summary of those observations. That limited exception is not permission to speculate, diagnose a condition or answer a question requiring specialized expertise.
The ordinary-observation exception
In Graat v. The Queen, [1982] 2 S.C.R. 819, the Supreme Court accepted non-expert opinions about alcohol impairment based on personal observations. The decision recognizes that some impressions cannot conveniently be separated from the facts that produced them. The subject must be within ordinary experience, and the witness must have a proper observational basis.
A witness describing someone as apparently intoxicated should be able to explain what they observed—for example, the person’s speech, balance or driving. The opinion is not automatically decisive. Graat also cautions against giving a police officer’s lay opinion preferential treatment simply because of the officer’s occupation or experience.
Describe the observations behind the conclusion
Explain what you actually saw or heard and your opportunity to observe it.
Distinguish the observation from the conclusion you drew.
Identify any limits: distance, lighting, noise, a brief encounter or missing context.
Do not turn information supplied by someone else into something you claim to have observed.
Do not present a guess about a person’s knowledge, intentions or medical condition as a fact.
An everyday description such as “she appeared upset” is different from a diagnosis or a conclusion about why she reacted that way. The same outward behaviour may have different explanations. The court must consider whether the evidence is relevant and whether the proposed inference is supported, rather than based on assumptions about how people ought to behave.
Admissibility is different from weight
The judge decides whether the evidence may be received, including applicable exclusionary rules and the risk of unfair prejudice. If admitted, the judge or jury still decides how much weight it deserves. Cross-examination may explore what the witness observed, alternative explanations and the limits of the opinion. A familiar label does not prove an essential element of the charge.
Witness capacity and hearsay raise separate questions
An opinion that a witness cannot testify is not the same as proof that their out-of-court statement can replace testimony. In R. v. Parrott, 2001 SCC 3, the Supreme Court rejected reliance on unsupported assumptions about a witness’s ability to communicate. Where a witness is available and no trauma from attempting testimony is suggested, their evidence should generally not be pre-empted by hearsay without the judge having an opportunity to assess them. Necessity, reliability, testimonial capacity and potential harm require their own analysis; no blanket rule makes an expert assessment mandatory in every case.
Know when specialist evidence is needed
Technical causation, a medical diagnosis or other matters outside ordinary experience may require a properly qualified expert and a separate admissibility assessment. Part 4 — Opinions of Experts explains that framework. Part 3 — Believe What I Say addresses credibility and reliability. Review the proposed evidence with counsel before trial rather than assuming that calling it a personal impression makes it admissible.
Continue the Testifying series
Part 5 — Non-Expert Opinion Evidence (this article)
Related guidance
For advice about your circumstances, contact our office. This article provides general information, not legal advice.