Witnesses Basics

Last Reviewed: March 2023 Reviewed by: JES Download

Witnesses Basics

Most evidence is introduced to the court through witnesses giving oral testimony (spoken evidence given under oath).

Rule 12-5(27) says that unless another statute or Rule says something different, a witness at a trial shall testify:

  • In open court and
  • Orally (unless the parties agree otherwise)

Key Terms

A witness is a person who gives evidence to the court orally under oath or affirmation or by affidavit (a sworn written statement).

Witnesses can be the parties themselves, or others who have particular knowledge or information about the dispute. Witnesses are a critical part of the trial process, whether they are giving evidence about what they saw happen or confirming that a document is authentic. A witness must be prepared to answer questions and give good information to the court.

There are generally speaking 2 types of witnesses: 

  • Lay Witness A “lay” witness is an ordinary witness who has been called to give evidence only on the facts that they observed, not to offer a professional or “expert” opinion on an issue at trial. Most witnesses are lay witnesses
  • Expert Witness An expert is someone qualified with special knowledge, skill, training, and experience, like an engineer or a doctor. For more information on expert witnesses, see Expert Witnesses.

Opinion Evidence

Opinions of Lay Witness

Opinions of Expert Witness 

Admissible if it is based on personal observation of something that is commonly known. The judge will decide whether the opinion is an assessment that ordinary people with ordinary experience and common knowledge are able to make.

For example, a lay witness may be able to give an opinion about the speed of a car that they saw driving down the street, but not the speed of an airplane that was flying overhead.

An expert can express an opinion based on information that they have personally observed, or information that was provided by others.

For example, an expert in motor vehicle accident analysis could go to the scene of the accident, measure skid marks, and give the court an expert opinion about the speed of the cars involved in the accident. Or, the expert might be able to give an opinion based on photographs of the accident scene.

It is usually a good idea to ask the judge to exclude witnesses during the trial. This means that they have to wait outside the courtroom until it is their time to give evidence. It prevents the witnesses from hearing each other’s testimony and changing their evidence in response to what they’ve heard.

Telling the Truth

Before a witness gives evidence to the court, they must agree to tell the truth.

Witnesses can take an oath to tell the truth by placing a hand on a religious text (like the Bible) and swearing that the evidence they give will be true. Or, witnesses can make a solemn affirmation that they will tell the truth. In this case, there is no religious meaning to the commitment to tell the truth.

The judge will give the same amount of weight to evidence given whether the witness takes an oath to tell the truth or affirms to tell the truth.


A witness must be competent to give evidence. This means that they must have the mental ability (called capacity) to give accurate evidence.

Except in the most extreme circumstances (for example, a witness with a severe brain injury), anyone can be called as a witness in your case. Remember, however, that the evidence must be relevant and material to your case. If your witness cannot give accurate and believable information to the court, the judge will not attach much importance to it.

The evidence of children is an exception to this general principle that anyone can be called to give evidence. The BC Evidence Act (s. 5), states that children over the age of 14 are presumed to be competent to testify in court. The other party can challenge that presumption, and it will be up to the court to decide whether the child is capable of giving good evidence.

The court must make a decision whether to allow evidence from children under 14. In general, young children must be able to understand the nature of an oath or solemn affirmation and be able to communicate the evidence to the court.

Requirement to Give Evidence

Witnesses who do not want to testify or cannot be relied upon to come to court can be compelled (required) to give evidence at trial by serving them (Formally giving them a legal document at their home or place of work) with a subpoena. A subpoena is a legal document that tells a witness that they are required to attend court to give evidence.

If witnesses under subpoena do not appear in court to give evidence, a warrant can be issued for their arrest and they can be brought to court to testify.

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