(1) Subject to section 15, a person who is incapable of understanding that, in giving evidence, he or she is under an obligation to give truthful evidence is not competent to give evidence.
(2) A person who is incapable of giving a rational reply to a question about a fact is not competent to give evidence about the fact.
(3) Where—
(a) a person is incapable of hearing or understanding, or of communicating a reply to, a question about a fact; and
(b) that incapacity cannot be overcome, or cannot be overcome without undue cost or undue delay,
the person is not competent to give evidence about the fact.
(4) Unless it appears otherwise, it shall be presumed that a person is not incompetent by reason of subsection (1), (2) or (3).
(5) Evidence that has been given by a witness does not become inadmissible by reason only that, before the witness finishes giving evidence, he or she dies or ceases to be competent to give evidence.
(6) For the purpose of determining a question arising under this section, the court may inform itself as the court thinks fit.