---
title: "Summa Theologica, First Half"
author: "Thomas Aquinas"
translator: "Fathers of the English Dominican Province"
languages: [en]
shelf: "Medieval"
section: 1155 of 1210
url: https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/1155/
cite: "Thomas Aquinas, tr. Fathers of the English Dominican Province, Summa Theologica, First Half, section 1155. Scriptura (scriptura.si), https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/1155/"
---

# Summa Theologica, First Half

*Thomas Aquinas, tr. Fathers of the English Dominican Province*

God and creation, human action, law and grace, then faith, hope, charity and justice.

## 1155. II–II · Q. 98, Art. 2: Whether all perjury is sinful?

Source: https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/1155/ · cite a paragraph as https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/1155/#p-N

[¶0] Whether all perjury is sinful?

[¶1] 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.

[¶2] 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.

[¶3] 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.

[¶4] 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.

[¶5] 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."

[¶6] I answer that, As stated above (Q 89, A 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.

[¶7] 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.

[¶8] 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.

[¶9] 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.

[¶10] 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.

[¶11] 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 (FS, Q 96, A 4).

### II–II · Q. 98, Art. 3: Whether all perjury is a mortal sin?

[¶13] Whether all perjury is a mortal sin?

[¶14] Objection 1: It would seem that not all perjury is a mortal sin. It is laid down (Extra, De Jurejur, cap. Verum): "Referring to the question whether an oath is binding on those who have taken one in order to safeguard their life and possessions, we have no other mind than that which our predecessors the Roman Pontiffs are known to have had, and who absolved such persons from the obligations of their oath. Henceforth, that discretion may be observed, and in order to avoid occasions of perjury, let them not be told expressly not to keep their oath: but if they should not keep it, they are not for this reason to be punished as for a mortal sin." Therefore not all perjury is a mortal sin.

[¶15] OBJ 2. Further, as Chrysostom [*Hom. xliv in the Opus Imperfectum on St. Matthew, falsely ascribed to St. John Chrysostom] says, "it is a greater thing to swear by God than by the Gospels." Now it is not always a mortal sin to swear by God to something false; for instance, if we were to employ such an oath in fun or by a slip of the tongue in the course of an ordinary conversation. Therefore neither is it always a mortal sin to break an oath that has been taken solemnly on the Gospels.

[¶16] Objection 3: Further, according to the Law a man incurs infamy through committing perjury (VI, qu. i, cap. Infames). Now it would seem that infamy is not incurred through any kind of perjury, as it is prescribed in the case of a declaratory oath violated by perjury [*Cap. Cum dilectus, de Ord. Cognit.]. Therefore, seemingly, not all perjury is a mortal sin.

[¶17] On the contrary, Every sin that is contrary to a divine precept is a mortal sin. Now perjury is contrary to a divine precept, for it is written (Lev. 19:12): "Thou shalt not swear falsely by My name." Therefore it is a mortal sin.

[¶18] I answer that, According to the teaching of the Philosopher (Poster. i, 2), "that which causes a thing to be such is yet more so." Now we know that an action which is, by reason of its very nature, a venial sin, or even a good action, is a mortal sin if it be done out of contempt of God. Wherefore any action that of its nature, implies contempt of God is a mortal sin. Now perjury, of its very nature implies contempt of God, since, as stated above (A 2), the reason why it is sinful is because it is an act of irreverence towards God. Therefore it is manifest that perjury, of its very nature, is a mortal sin.

[¶19] Reply to Objection 1: As stated above (Q 89, A 7, ad 3), coercion does not deprive a promissory oath of its binding force, as regards that which can be done lawfully. Wherefore he who fails to fulfil an oath which he took under coercion is guilty of perjury and sins mortally. Nevertheless the Sovereign Pontiff can, by his authority, absolve a man from an obligation even of an oath, especially if the latter should have been coerced into taking the oath through such fear as may overcome a high-principled man.

[¶20] When, however, it is said that these persons are not to be punished as for a mortal sin, this does not mean that they are not guilty of mortal sin, but that a lesser punishment is to be inflicted on them.

[¶21] Reply to Objection 2: He that swears falsely in fun is nonetheless irreverent to God, indeed, in a way, he is more so, and consequently is not excused from mortal sin. He that swears falsely by a slip of tongue, if he adverts to the fact that he is swearing, and that he is swearing to something false, is not excused from mortal sin, as neither is he excused from contempt of God. If, however, he does not advert to this, he would seem to have no intention of swearing, and consequently is excused from the sin of perjury.

[¶22] It is, however, a more grievous sin to swear solemnly by the Gospels, than to swear by God in ordinary conversation, both on account of scandal and on account of the greater deliberation. But if we consider them equally in comparison with one another, it is more grievous to commit perjury in swearing by God than in swearing by the Gospels.

[¶23] Reply to Objection 3: Not every sin makes a man infamous in the eye of the law. Wherefore, if a man who has sworn falsely in a declaratory oath be not infamous in the eye of the law, but only when he has been so declared by sentence in a court of law, it does not follow that he has not sinned mortally. The reason why the law attaches infamy rather to one who breaks a promissory oath taken solemnly is that he still has it in his power after he has sworn to substantiate his oath, which is not the case in a declaratory oath.