De testibus et testimoniis theses L

XXXV.
For it is the office of the judge not so much to spare the expenses of the parties as to investigate the truth by whatever means he can.

XXXVI.
His voice and the gravity of his person will aid greatly in this inquiry. For the nature of many is such that, while they can shamelessly lie outside of court, once they see the judge's face, they are compelled by a certain natural fear and confess immediately, so that from the speech, constancy, and trembling of men, much emerges into the light to illuminate the truth.

XXXVII.
The parties, however, must apply the utmost reason and counsel in producing witnesses. For just as that action is empty which the miserable poverty of a debtor elicits immediately, so those witnesses are useless whom a single exception from the opposing party drives away from testifying.

XXXVIII.
Therefore, let them produce, as far as they can, those who are above any exception: and let them not be so instructed that suspicion arises from premeditated speech, nor so inept that if they testify to something ambiguous, it acts against those producing them. For it is the behavior of an inconsiderate person to bring such witnesses into court through whom trouble is made for himself.

XXXIX.
Let them know the fidelity and constancy of men; the former, so that there may be authority in their words; the latter, so that they are always consistent with themselves. For those whose fidelity wavers should not be employed to provide proof of an accomplished fact.

XL.
We consider fidelity to waver when witnesses testify to contradictory things: if these can be reconciled by some probable reason, it is certainly necessary to reconcile them, not so that they might provide proof, but so that the witnesses might avoid the penalties for perjury.