2. Human testimony can seldom acquire the certainty of demonstration. Witnesses not unfrequently are mistaken or wish to deceive; the most that can be expected is that moral certainty which arises from analogy. The credibility which is attached to such testimony, arises. from the double presumption that the witnesses have good sense and intelligence, and that they are not mistaken nor deceived; they are further presumed to have probity, and that they do not wish to deceive.
3. To gain credibility, we must be assured, first, that the witness has not been mistaken nor deceived. To be assured as far as possible on this subject, it is proper to consider the nature and quality of the facts proved; the quality and person of the witness; the testimony in itself; and to compare it with the depositions of other witnesses on the subject, and with known facts. Secondly, we must be satisfied that he does not wish to deceive: there are strong assurances of this, when the witness is under oath, is a man of integrity, and disinterested. Vide Arch. Civ. Pl. 444; 5 Com. Dig. 449; 8 Watts, R. 227; Competency.