The traditional rule is that a party is not allowed to impeach his own witness. Note: A bias may be implied in the case of family, but this fact cannot be used to impeach the witness. The exceptions to the traditional rule that a party is not allowed to impeach his own witnesses are: (1) The witness is required to testify by law. (2) The witness is an adverse party. (3) The witness is hostile on the stand or the party calling the witness is legitimately surprised by the testimony. The traditional rule can never be applied in a criminal action if it deprives the accused of a fair trial as guaranteed by the fourteenth amendment. The modern trend allows the impeachment of any witness by any party. The rationale is that there is really no control over who can be called to be a witness to an action: there may be only one witness to an accident, etc.