When suit is in a trial stage then both the parties submit evidences before the court to prove or disprove the case. the evidence may be produce in two ways one by producing relevant documents another by producing the person who are acquainted with fact of the case. these persons are called as witness. Every person are not competent to testify as a witness in the court of Law.
In The word of section 118 of Evidence Act 1872:
All persons shall be competent to testify unless the Court considers that they are prevented from understanding the questions put to them, or from giving rational answers to those questions, by tender years, extreme old age, disease, whether of body or mind, or any other cause of the same kind.
So, we can say that,
The competency of a witness depends upon the circumstances that exist when the testimony is given. Age, mental power, and capacity to understand the nature and obligation of an oath are the tests that determine the competency of a witness. An expert witness should possess special knowledge of the subject on which the jury’s knowledge would be inadequate without expert assistance.
A person can be a witness if s/he has sufficient intelligence to understand the nature of an oath and to give a reasonably accurate account of what the person has seen and heard regarding the matter in question. A competent witness should be capable of receiving, remembering, and narrating impressions. A witness should also be sensible to the obligation of an oath before the person can be permitted to testify.
A witness cannot be considered incompetent because of intoxication. However, if the person was virtually unconscious at the time of the event, the person can be considered incompetent. Persons intoxicated at the time they are offered as witnesses are excluded from testifying. Use of drugs also does not render a witness incompetent. However, addiction to drugs can affect the credibility and weight of the person’s testimony.
When a person is insane or mentally ill, it does not automatically render him/her an incompetent witness[v]. The court tests whether the person affected with insanity has sufficient knowledge to apprehend the obligation of an oath and whether h/she is capable to give a correct account of the matters which the person has seen or heard, then the person can be considered a competent witness. The person should also be capable to perceive and narrate.
The testimony of a convicted felon cannot be considered inadmissible. However, the weight of the evidence can be questioned.
A child can be a competent witness if the child has an understanding of the obligation to speak the truth on the witness stand, the mental capacity at the time of the occurrence concerning which s/he is to testify to receive an accurate impression of it, a memory sufficient to retain an independent recollection of the occurrence, the capacity to express in words his/her memory of the occurrence, and the capacity to understand simple questions about the matter. A child of any age can testify if the child meets the statutory requirements of a competent witness.
A witness who is unable to speak may give his evidence in any other manner in which he can make it intelligible,
as by writing or by signs; but such writing must be written and the signs made in open Court. Evidence so given shall be deemed to be oral evidence.
So it is not fact that the person who appear before the court to give his or her testimony but the fact is whether s/he is mature enough to understand the question put to him.