At common law the general rule is that ‘the opinions, beliefs and inferences of a witness were inadmissible to prove the truth of the matters believed or inferred if such matters were in issue or relevant to facts in issue in the case. It was also held that opinion evidence assumed the role of the court to form an opinion on the facts in issue based on the facts proved by the evidence placed before it. However, opinion evidence was admitted for other purposes, for instance, for proving the state of mind of the holder of an opinion at a certain time if it was relevant to do so. In general, opinions of witnesses are not admissible and evidence by witnesses is limited only to stating facts. The general rule of opinion evidence is subject to the following exceptions:
The evidence of general reputation is admissible to prove matters of public concern which would otherwise be impossible or very difficult to prove.
The evidence of expert opinion is admissible to prove matters of specialized knowledge without which the court would be unable to reach a conclusion properly.
The evidence of non-expert opinion may be received on matters within the competence and experience of lay persons generally.
Opinion evidence may be in the form of hearsay statements where opinion evidence is admissible and such statements are important only in relation to expert opinion evidence and are known as expert reports.
