Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that he who demands an oath of a perjurer commits a sin. Either he knows that he swears truly, or he knows that he swears falsely. If he knows him to swear truly, it is useless for him to demand an oath: and if he believes him to swear falsely, for his own part he leads him into sin. Therefore nowise seemingly should one enjoin an oath on another person.

Objection 2: Further, to receive an oath from a person is less than to impose an oath on him. Now it would seem unlawful to receive an oath from a person, especially if he swear falsely, because he would then seem to consent in his sin. Much less therefore would it seem lawful to impose an oath on one who swears falsely.

Objection 3: Further, it is written (Lev. 5:1): "If anyone sin, and hear the voice of one swearing falsely , and is a witness either because he himself hath seen, or is privy to it: if he do not utter it, he shall bear his iniquity." Hence it would seem that when a man knows another to be swearing falsely, he is bound to denounce him. Therefore it is not lawful to demand an oath of such a man.

Objection 4: On the other hand, Just as it is a sin to swear falsely so is it to swear by false gods. Yet it is lawful to take advantage of an oath of one who has sworn by false gods, as Augustine says (ad Public. Ep. xlvii). Therefore it is lawful to demand an oath from one who swears falsely.

I answer that, As regards a person who demands an oath from another, a distinction would seem to be necessary. For either he demands the oath on his own account and of his own accord, or he demands it on account of the exigencies of a duty imposed on him. If a man demands an oath on his own account as a private individual, we must make a distinction, as does Augustine (de Perjuriis. serm. clxxx): "For if he knows not that the man will swear falsely, and says to him accordingly: 'Swear to me' in order that he may be credited, there is no sin: yet it is a human temptation" (because, to wit, it proceeds from his weakness in doubting whether the man will speak the truth). "This is the evil whereof Our Lord says (Mt. 5:37): That which is over and above these, is of evil. But if he knows the man to have done so," i.e. the contrary of what he swears to, "and yet forces him to swear, he is a murderer: for the other destroys himself by his perjury, but it is he who urged the hand of the slayer."

If, on the other hand, a man demands an oath as a public person, in accordance with the requirements of the law, on the requisition of a third person: he does not seem to be at fault, if he demands an oath of a person, whether he knows that he will swear falsely or truly, because seemingly it is not he that exacts the oath but the person at whose instance he demands it.

Reply to Objection 1: This argument avails in the case of one who demands an oath on his own account. Yet he does not always know that the other will swear truly or falsely, for at times he has doubts about the fact, and believes he will swear truly. In such a case he exacts an oath in order that he may be more certain.

Reply to Objection 2: As Augustine says (ad Public. serm. xlvii), "though we are forbidden to swear, I do not remember ever to have read in the Holy Scriptures that we must not accept oaths from others." Hence he that accepts an oath does not sin, except perchance when of his own accord he forces another to swear, knowing that he will swear falsely.

Reply to Objection 3: As Augustine says (Questions. Super Lev, qu. i), Moses in the passage quoted did not state to whom one man had to denounce another's perjury: wherefore it must be understood that the matter had to be denounced "to those who would do the perjurer good rather than harm." Again, neither did he state in what order the denunciation was to be made: wherefore seemingly the Gospel order should be followed, if the sin of perjury should be hidden, especially when it does not tend to another person's injury: because if it did, the Gospel order would not apply to the case, as stated above (Question 33, Article 7; Question 68, Article 1).

Reply to Objection 4: It is lawful to make use of an evil for the sake of good, as God does, but it is not lawful to lead anyone to do evil. Consequently it is lawful to accept the oath of one who is ready to swear by false gods, but it is not lawful to induce him to swear by false gods. Yet it seems to be different in the case of one who swears falsely by the true God, because an oath of this kind lacks the good of faith, which a man makes use of in the oath of one who swears truly by false gods, as Augustine says (ad Public. Ep. xlvii). Hence when a man swears falsely by the true God his oath seems to lack any good that one may use lawfully.

Articulus 4

Argumentum 1

Ad quartum sic proceditur. Videtur quod peccet ille qui iniungit iuramentum ei qui periurat. Aut enim scit eum verum iurare, aut falsum. Si scit eum verum iurare, pro nihilo ei iuramentum iniungit si autem credit eum falsum iurare, quantum est de se, inducit eum ad peccandum. Ergo videtur quod nullo modo debeat aliquis alicui iniungere iuramentum.

Argumentum 2

Praeterea, iuramentum minus est accipere ab aliquo quam iuramentum iniungere alicui. Sed recipere iuramentum ab aliquo non videtur esse licitum, et praecipue si periuret, quia in hoc videtur consentire peccato. Ergo videtur quod multo minus liceat exigere iuramentum ab eo qui periurat.

Argumentum 3

Praeterea, dicitur Levit. V, si peccaverit anima, et audierit vocem iurantis falsum, testisque fuerit quod aut ipse vidit aut conscius est, nisi indicaverit, portabit iniquitatem suam, ex quo videtur quod aliquis sciens aliquem iurare falsum, teneatur eum accusare. Non igitur licet ab eo exigere iuramentum.

Sed Contra

Sed contra, sicut peccat ille qui falsum iurat, ita ille qui per falsos deos iurat. Sed licet uti iuramento eius qui per falsos deos iurat, ut Augustinus dicit, ad Publicolam.

Ergo licet iuramentum exigere ab eo qui falsum iurat.

Corpus

Respondeo dicendum quod circa eum qui exigit ab alio iuramentum, distinguendum videtur. Aut enim exigit iuramentum pro seipso propria sponte, aut exigit iuramentum pro alio ex necessitate officii sibi commissi. Et si quidem aliquis pro seipso exigit iuramentum tanquam persona privata, distinguendum videtur, ut Augustinus dicit, in sermone de periuriis.

Si enim nescit eum iuraturum falsum, et ideo dicit, iura mihi, ut fides ei sit, non est peccatum, tamen est humana tentatio, quia scilicet procedit ex quadam infirmitate, qua homo dubitat alium esse verum dicturum.

Et hoc est illud malum de quo dominus dicit, Matth. V, quod amplius est, a malo est. Si autem scit eum fecisse, scilicet contrarium eius quod iurat, et cogit eum iurare, homicida est. Ille enim de suo periurio se interimit, sed iste manum interficientis impressit.

Si autem aliquis exigat iuramentum tanquam persona publica, secundum quod exigit ordo iuris, ad petitionem alterius, non videtur esse in culpa si ipse iuramentum exigat, sive sciat eum falsum iurare sive verum, quia non videtur ille exigere, sed ille ad cuius instantiam exigit.

Ad 1

Ad primum ergo dicendum quod obiectio illa procedit quando pro aliquis exigit iuramentum. Et tamen non semper scit eum iurare verum, vel falsum, sed quandoque dubitat de facto, et credit eum verum iuraturum, et tunc ad maiorem certitudinem exigit iuramentum.

Ad 2

Ad secundum dicendum quod, sicut Augustinus dicit, ad Publicolam, quamvis dictum sit ne iuremus, nunquam me in Scripturis sanctis legisse memini ne ab aliquo iurationem accipiamus.

Unde ille qui iurationem recipit non peccat, nisi forte quando propria sponte ad iurandum cogit eum quem scit falsum iuraturum.

Ad 3

Ad tertium dicendum quod, sicut Augustinus dicit, Moyses non expressit in praedicta auctoritate cui sit indicandum periurium alterius. Et ideo intelligitur quod debeat indicari talibus qui magis possunt prodesse quam obesse periuro.

Similiter etiam non expressit quo ordine debeat manifestare.

Et ideo videtur servandus ordo evangelicus, si sit peccatum periurii occultum, et praecipue quando non vergit in detrimentum alterius, quia in tali casu non haberet locum ordo evangelicus, ut supra dictum est.

Ad 4

Ad quartum dicendum quod licet uti malo propter bonum, sicut et deus utitur, non tamen licet aliquem ad malum inducere. Unde licet eius qui paratus est per falsos deos iurare, iuramentum recipere, non tamen licet eum inducere ad hoc quod per falsos deos iuret. Alia tamen ratio esse videtur in eo qui per verum deum falsum iurat. Quia in tali iuramento deest bonum fidei, qua utitur aliquis in iuramento illius qui verum per falsos deos iurat, ut Augustinus dicit, ad Publicolam.

Unde in iuramento eius qui falsum per verum deum iurat, non videtur esse aliquod bonum quo uti liceat.