IEA Section 155

The credit of a witness may be impeached in the following ways by the adverse party, or with the consent of the Court, by the party who calls him—

1. By the evidence of persons who testify that they, from their knowledge of the witness believe him to be unworthy of credit;
2. By proof that the witness has been bribed, or has accepted the offer of a bribe, or has received any other corrupt inducement to give his evidence;
3. By proof of former statements inconsistent with any part of his evidence which is liable to be contradicted;