Husbands and wives are, in all civil and criminal cases, competent witnesses against each other, subject to the qualification that communications between the spouses made during marriage are protected from disclosure.
In all civil proceedings, the parties to the suit are competent witnesses. Therefore, a party to a suit can call as his witness any of the defendants to the suit. And although an accused person is incompetent to testify in proceedings in which he is an accused, an accomplice is a competent witness against an accused person. All persons are competent to testify, unless prevented from. (a) Understanding the questions, or (b) Giving rational answers By reason of- (i) Tender years, (ii) Extreme old age, (iii) Disease of body or mind, or (iv) Any other similar cause. (S. 118) A lunatic is competent to testify – unless he is prevented by lunacy from understanding the questions and giving rational answers to them.
(S. 118) A witness who is unable to speak may give evidence in any manner in which he can make it intelligible, e.g., by writing or by signs in open Court. Such evidence shall be deemed to be oral evidence.
(S. 119) A witness who has taken a religious vow of silence is deemed to be “unable to speak”, and he may give his evidence in writing to questions put to him. (Lakshan Singh v. Emperor, (1941) 20 Pat. 898) When a deaf-mute witness is to be examined, the Court has to ascertain, before he is examined, that he has the necessary amount of intelligence and that he understands the nature of the oath and of the questions put to him.