Evidence. The benefit which a person has in the matter about to be decided and which is in issue between the parties. By the term benefit is here understood some pecuniary or other advantage, which if obtained, would increase the, witness estate, or some loss, which would decrease it.
2. It is a general rule that a party who has an interest in the cause cannot be a witness. It will be proper to consider this matter by taking a brief view of the thing or subject in dispute, which is the object of the interest; the quantity of interest; the quality of interest; when an interested witness can be examined; when the interest must exist; how an interested witness can be rendered competent.
3. - 1. To be disqualified on the ground of interest, the witness must gain or lose by the event of the cause, or the verdict must be lawful evidence for or against him in another suit, or the record must be an instrument of evidence
for or against him. 3 John. Cas. 83; 1 Phil. Ev. 36; Stark. Ev. pt. 4, p. 744. But an interest in the question does not disqualify the witness. 1 Caines, 171; 4 John. 302; 5 John. 255; 1 Serg. & R. 82, 36; 6 Binn. 266; 1 H. & M. 165, 168.
4. - 2. The magnitude
of the interest is altogether immaterial, even a liability for the most trifling costs will be sufficient. 5 T. R. 174; 2 Vern. 317; 2 Greenl. 194; 11 John. 57.
5. - 3. With regard to the quality, the interest must be legal, as contradistinguished from mere prejudice or bias
, arising from relationship, friendship, or any of the numerous motives by which a witness may be supposed to be influenced. Leach, 154; 2 St. Tr. 334, 891; 2 Hawk. ch. 46, s. 25. It must be a present, certain, vested interest
, and not uncertain and contingent. Dougl. 134; 2 P. Wms. 287; 3 S. & R. 132; 4 Binn. 83; 2 Yeates, 200; 5 John. 256; 7 Mass. 25. And it must have been acquired without fraud. 3 Camp. 380; l M. & S. 9; 1 T. R. 37.
6. - 4. To the general rule that interest renders a witness incompetent, there are some exceptions. First. Although the witness may have an interest, yet if his interest is equally strong on the other side, and no more, the witness is reduced to a state of neutrality by an equipoise of interest, and the objection to his testimony ceases. 7 T. R. 480, 481, n.; 1 Bibb, R. 298; 2 Mass. R. 108; 2 S. & R. 119; 6 Penn. St. Rep. 322.
7. Secondly. In some instances the law admits the testimony of one interested, from the extreme necessity of the case; upon this ground the servant of a tradesman is admitted to prove the delivery of goods and the payment of money, without any release from the master. 4 T. R. 490; 2 Litt. R. 27.
8. - 5. The interest, to render the witness disqualified, must exist at the time of his examination. A deposition made at a time when the witness had no interest, may be read in evidence
, although he has afterwards acquired an interest. 1 Hoff. R. 21.
9. - 6. The objection to incompetency on the ground of interest may be removed by an extinguishment of that interest by means of a release, executed either by the witness, when he would receive an advantage by his testimony, or by those who have a claim upon him when his testimony would be evidence of his liability. The objection may also be removed by payment. Stark. Ev. pt. 4, p. 757. See Benth. Rationale
of Jud. Ev. 628-692, where he combats the established doctrines of the law, as to the exclusion
on the ground of interest; and Balance.