To determine exactly the credibility of a witness, and the force of evidence, is an important point in every good legislation. Every man of common sense, that is, every one whose ideas have some connexion with each other, and whose sensations are conformable to those of other men, may be a witness; but the credibility of his evidence will be in proportion as he is interested in declaring or concealing the truth. Hence it appears, how frivolous is the reasoning of those, who reject the testimony of women on account of their weakness; how puerile it is, not to admit the evidence of those who are under sentence of death, because they are dead in law; and how irrational, to exclude persons branded with infamy: for in all these cases they ought to be credited, when they have no interest in giving false testimony.

The credibility of a witness, then, should only diminish in proportion to the hatred, friendship, or connexions subsisting between him and the delinquent. One witness is not sufficient; for whilst the accused denies what the other affirms, truth remains suspended, and the right that every one has to be believed innocent, turns the balance in his favour.

The credibility of a witness is the less, as the atrociousness of the crime is greater, from the improbability of its having been committed; as in cases of witchcraft, and acts of wanton cruelty. The writers on penal laws have adopted a contrary principle, viz., that the credibility of a witness is greater, as the crime is more atrocious. Behold their inhuman maxim, dictated by the most cruel imbecility. In atrocissimis, leviores conjecturæ sufficiunt, & licet judici jura transgredi. Let us translate this sentence, that mankind may see one of the many unreasonable principles to which they are ignorantly subject. In the most atrocious crimes the slightest conjectures are sufficient, and the judge is allowed to exceed the limits of the law. The absurd practices of legislators are often the effect of timidity, which is a principal source of the contradictions of mankind. The legislators, (or rather lawyers, whose opinions, when alive, were interested and venal, but which after their death become of decisive authority, and are sovereign arbiters of the lives and fortunes of men), terrified by the condemnation of some innocent person, have burdened the law with pompous and useless formalities, the scrupulous observance of which will place anarchical impunity on the throne of justice; at other times, perplexed by atrocious crimes of difficult proof, they imagined themselves under a necessity of superseding the very formalities established by themselves; and thus, at one time, with despotic impatience, and at another with feminine timidity, they transform their solemn judgments into a game of hazard.

But to return. In the case of witchcraft, it is much more probable, that a number of men should be deceived, than that any person should exercise a power which God hath refused to every created being. In like manner, in cases of wanton cruelty, the presumption is always against the accuser, without some motive of fear or hate. There are no spontaneous or superfluous sentiments in the heart of man; they are all the result of impressions on the senses.

The credibility of a witness may also be diminished, by his being a member of a private society, whose customs and principles of conduct are either not known, or are different from those of the public. Such a man has not only his own passions, but those of the society of which he is a member.

Finally, the credibility of a witness is null, when the question relates to the words of a criminal; for the tone of voice, the gesture, all that precedes, accompanies and follows the different ideas which men annex to the same words, may so alter and modify a man’s discourse, that it is almost impossible to repeat them precisely in the manner in which they were spoken. Besides, violent and uncommon actions, such as real crimes, leave a trace in the multitude of circumstances that attend them, and in their effects; but words remain only in the memory of the hearers, who are commonly negligent or prejudiced. It is infinitely easier then to found an accusation on the words, than on the actions of a man; for in these, the number of circumstances, urged against the accused, afford him variety of means of justification.