Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that not all perjury is sinful. Whoever does not fulfil what he has confirmed on oath is seemingly a perjurer. Yet sometimes a man swears he will do something unlawful (adultery, for instance, or murder): and if he does it, he commits a sin. If therefore he would commit a sin even if he did it not, it would follow that he is perplexed.

Objection 2: Further, no man sins by doing what is best. Yet sometimes by committing a perjury one does what is best: as when a man swears not to enter religion, or not to do some kind of virtuous deed. Therefore not all perjury is sinful.

Objection 3: Further, he that swears to do another's will would seem to be guilty of perjury unless he do it. Yet it may happen sometimes that he sins not, if he do not the man's will: for instance, if the latter order him to do something too hard and unbearable. Therefore seemingly not all perjury is sinful.

Objection 4: Further, a promissory oath extends to future, just as a declaratory oath extends to past and present things. Now the obligation of an oath may be removed by some future occurrence: thus a state may swear to fulfil some obligation, and afterwards other citizens come on the scene who did not take the oath; or a canon may swear to keep the statutes of a certain church, and afterwards new statutes are made. Therefore seemingly he that breaks an oath does not sin.

On the contrary, Augustine says (De Verb. Apost. Jacobi; Serm. cxxx), in speaking of perjury: "See how you should detest this horrible beast and exterminate it from all human business."

I answer that, As stated above (Question 89, Article 1), to swear is to call God as witness. Now it is an irreverence to God to call Him to witness to a falsehood, because by so doing one implies either that God ignores the truth or that He is willing to bear witness to a falsehood. Therefore perjury is manifestly a sin opposed to religion, to which it belongs to show reverence to God.

Reply to Objection 1: He that swears to do what is unlawful is thereby guilty of perjury through lack of justice: though, if he fails to keep his oath, he is not guilty of perjury in this respect, since that which he swore to do was not a fit matter of an oath.

Reply to Objection 2: A person who swears not to enter religion, or not to give an alms, or the like, is guilty of perjury through lack of judgment. Hence when he does that which is best it is not an act of perjury, but contrary thereto: for the contrary of that which he is doing could not be a matter of an oath.

Reply to Objection 3: When one man swears or promises to do another's will, there is to be understood this requisite condition---that the thing commanded be lawful and virtuous, and not unbearable or immoderate.

Reply to Objection 4: An oath is a personal act, and so when a man becomes a citizen of a state, he is not bound, as by oath, to fulfil whatever the state has sworn to do. Yet he is bound by a kind of fidelity, the nature of which obligation is that he should take his share of the state's burdens if he takes a share of its goods.

The canon who swears to keep the statutes that have force in some particular "college" is not bound by his oath to keep any that may be made in the future, unless he intends to bind himself to keep all, past and future. Nevertheless he is bound to keep them by virtue of the statutes themselves, since they are possessed of coercive force, as stated above (1.2, Question 96, Article 4).

Articulus 2

Argumentum 1

Ad secundum sic proceditur. Videtur quod non omne periurium sit peccatum. Quicumque enim non implet quod iuramento firmavit, periurus esse videtur. Sed quandoque aliquis iurat se facturum aliquid illicitum, puta adulterium vel homicidium, quod si faciat, peccat. Si ergo etiam non faciendo peccaret peccato periurii, sequeretur quod esset perplexus.

Argumentum 2

Praeterea, nullus peccat faciendo quod melius est. Sed quandoque aliquis periurando facit quod melius est, sicut cum aliquis iuravit se non intraturum religionem, vel quaecumque opera virtuosa non facturum. Ergo non omne periurium est peccatum.

Argumentum 3

Praeterea, ille qui iurat facere alterius voluntatem, nisi eam faciat, videtur incurrere periurium. Sed quandoque potest contingere quod non peccat si eius non impleat voluntatem, puta cum praecipit ei aliquid nimis durum et importabile.

Ergo videtur quod non omne periurium sit peccatum.

Argumentum 4

Praeterea, iuramentum promissorium se extendit ad futura, sicut assertorium ad praeterita et praesentia. Sed potest contingere quod tollatur obligatio iuramenti per aliquid quod in futurum emergat, sicut cum aliqua civitas iurat se aliquid servaturam, et postea superveniunt novi cives qui illud non iuraverunt; vel cum aliquis canonicus iurat statuta alicuius ecclesiae se servaturum, et postmodum aliqua fiunt de novo. Ergo videtur quod ille qui transgreditur iuramentum non peccet.

Sed Contra

Sed contra est quod Augustinus dicit, in sermone de verbis Apost. Iacobi, de periurio loquens, videtis quam ista detestanda sit belua, et de rebus humanis exterminanda.

Corpus

Respondeo dicendum quod, sicut supra dictum est, iurare est deum testem invocare. Pertinet autem ad dei irreverentiam quod aliquis eum testem invocet falsitatis, quia per hoc dat intelligere vel quod deus veritatem non cognoscat, vel quod falsitatem testificari velit. Et ideo periurium manifeste est peccatum religioni contrarium, cuius est deo reverentiam exhibere.

Ad 1

Ad primum ergo dicendum quod ille qui iurat se facturum aliquod illicitum, iurando incurrit periurium propter defectum iustitiae.

Sed si non impleat quod iuravit, in hoc periurium non incurrit, quia hoc non erat tale quid quod sub iuramento cadere posset.

Ad 2

Ad secundum dicendum quod ille qui iurat se non intraturum religionem, vel non daturum eleemosynam, vel aliquid huiusmodi, iurando periurium incurrit propter defectum iudicii. Et ideo quando facit id quod melius est, non est periurium, sed periurio contrarium, contrarium enim eius quod facit sub iuramento cadere non poterat.

Ad 3

Ad tertium dicendum quod cum aliquis iurat vel promittit se facturum voluntatem alterius, intelligenda est debita conditio, si scilicet id quod ei mandatur sit licitum et honestum, et portabile sive moderatum.

Ad 4

Ad quartum dicendum quod quia iuramentum est actio personalis, ille qui de novo fit civis alicuius civitatis, non obligatur quasi iuramento ad servanda illa quae civitas se servaturam iuravit.

Tenetur tamen ex quadam fidelitate, ex qua obligatur ut sicut fit socius bonorum civitatis, ita etiam fiat particeps onerum.

Canonicus vero qui iurat se servaturum statuta edita in aliquo collegio, non tenetur ex iuramento ad servandum futura, nisi intenderit se obligare ad omnia statuta praeterita et futura tenetur tamen ea servare ex ipsa VI statutorum, quae habent coactivam virtutem, ut ex supradictis patet.