ABSTRACT
The fundamental rule is that witnesses testify about facts and not about the opinions they have formed from facts. The reason for this is that it is the job of the ‘tribunal of fact’ (a judge or, very occasionally, a jury in a civil case, and magistrates or a jury in a criminal case) to hear the evidence, find facts, and make inferences from them. It is thought that the tribunal may be misled and hindered in its work if opinion evidence is too freely received. The pervasiveness of the rule can sometimes be forgotten in cross-examination. A witness should not generally be asked to give his opinion about what another witness has said. For example, in R v Windass2 an appeal against conviction was allowed where a defendant had been asked during cross-examination to interpret entries that his girlfriend had made in her diary without any contribution from him.
