Lord Hardwicke had before declared, with great truth, “that the boundaries of what goes to the credit and what to the competency are very nice, and the latter carried too far”; and in the same case he said, “that, unless the objection appeared to him to carry a strong danger of perjury, and some apparent advantage might accrue to the witness, he was always inclined to let it go to his credit, only in order to let in a proper light to the case, which would otherwise be shut out; and in a doubtful case, he said, it was generally his custom to admit the evidence, and give such directions to the jury as the nature of the case might require."[60]

It is a known rule of evidence, that an interest in the matter to be supported by testimony disqualifies a witness; yet Lord Mansfield held, “that nice objections to a remote interest which could not be paid or released, though they held in other cases, were not allowed to disqualify a witness to a will, as parishioners might have [prove?] a devise to the use of the poor of the parish forever.”  He went still nearer, and his doctrine tends so fully to settle the principles of departure from or adherence to rules of evidence, that your Committee inserts part of the argument at large.  “The disability of a witness from interest is very different from a positive incapacity.  If a deed must be acknowledged before a judge or notary public, every other person is under a positive incapacity to authenticate it; but objections of interest are deductions from natural reason, and proceed upon a presumption of too great a bias in the mind of the witness, and the public utility of rejecting partial testimony.  Presumptions stand no longer than till the contrary is proved.  The presumption of bias may be taken off by showing the witness has a [as?] great or a greater interest the other way, or that he has given it up.  The presumption of public utility may be answered by showing that it would be very inconvenient, under the particular circumstances, not to receive such testimony.  Therefore, from the course of business, necessity, and other reasons of expedience, numberless exceptions are allowed to the general rule."[61]

These being the principles of the latter jurisprudence, the Judges have suffered no positive rule of evidence to counteract those principles.  They have even suffered subscribing witnesses to a will which recites the soundness of mind in the testator to be examined to prove his insanity, and then the court received evidence to overturn that testimony and to destroy the credit of those witnesses.  They were five in number, who attested to a will and codicil.  They were admitted to annul the will they had themselves attested.  Objections were taken to the competency of one of the witnesses in support of the will against its subscribing witnesses:  1st, That the witness was an executor in trust, and so liable to actions; 2dly, As having acted under the trust, whereby, if