§ 4. On the Violation of an Oath, or Perjury

456. Definition. Perjury taken in the broad sense is any unlawful oath which, namely, lacks one of the three companions indicated above. Perjury in the strict sense (Meineid) is a moral lie confirmed by an oath. But perjury is not present if someone under oath asserts an error which he invincibly thinks to be the truth. If someone afterwards culpably does not fulfill a thing seriously promised under a promissory oath, he commits rather a breaking of the oath (Eidbruch) than perjury; nevertheless, he can truly be called perjured.

457. Principle 1. An oath pronounced with a defect of truth, or perjury strictly so called, is a mortal sin from its whole genus.

Thus holds the most common and certain opinion. Therefore Innocent XI condemned proposition 24: "To call God as witness to a light lie is not so great an irreverence that on account of it He wills or can condemn a man."⁶⁰¹ And among the questions to be proposed to Wycliffites and Hussites there is also this: "Whether he believes that perjury knowingly committed, from whatever cause or occasion, for the preservation of his own bodily life or that of another, even in favor of the faith, is a mortal sin?"⁶⁰² The intrinsic reason is that every perjury is essentially a notable injury and contempt of God, who can neither deceive nor be deceived. Therefore the Angelic Doctor⁶⁰³ says: "Those things which of themselves are venial sins, or even good in genus, if they are done in contempt of God, are mortal sins. Hence much more, whatever by its nature pertains to contempt of God is a mortal sin. But perjury by its nature imports contempt of God.... Hence it is manifest that perjury by reason of itself is a mortal sin.... He who perjures himself in jest does not avoid divine irreverence, but in some respect increases it more, and therefore he is not excused from mortal sin." Therefore, if even a jocose lie confirmed by an oath is a mortal sin, there is no slightness of matter in perjury; consequently, it is a mortal sin from its whole genus, i.e., it always induces the guilt of mortal sin unless there is an imperfection of the act because of insufficient knowledge or will. Since these things are so, it is easily understood why the most severe penalties against the perjured have been enacted by divine, ecclesiastical, and civil law. God Himself threatens the perjured with a curse and exclusion from the kingdom of heaven;⁶⁰⁴ the Church excludes the perjured from giving testimony and punishes them at the prudent judgment of the Ordinary;⁶⁰⁵ and civil laws are accustomed to punish the perjured with the penalty of grave imprisonment.⁶⁰⁶

Note. He also commits true perjury who swears with a purely mental restriction, as is clear from proposition 26 condemned by Innocent XI.⁶⁰⁷

Likewise, a feigned oath seems to be referred to perjury, as was already said above in n. 441.

⁶⁰¹ Denz., n. 1174.

⁶⁰² Denz., n. 664.

⁶⁰³ S. theol. 2, 2, q. 98, a. 3c and ad 2; cf. 3, dist. 39, q. 1, a. 5, sol. 1, where St. Thomas says: "If [someone] swears falsely, I believe that he always sins mortally, whether the oath is solemn or not solemn."

⁶⁰⁴ Cf. Zech. 5:3ff.

⁶⁰⁵ Code of Canon Law, c. 1757, § 2, n. 1; c. 1795, c. 2; c. 2323.

⁶⁰⁶ Cf. Penal Laws for the German Empire, § 153ff.

⁶⁰⁷ "If someone ... for any other end whatever should swear that he did not do something which he really did, understanding within himself something else which he did not do, or another way from that in which he did it, or anything else true added, he does not really lie nor is he perjured" (Denz., n. 1176).

458. Principle 2. An oath pronounced with a defect of judgment is from its genus a venial sin. Thus holds the common opinion.

The reason is that the irreverence inflicted upon God in this way does not seem to be so great as to constitute a mortal sin, because no divine attribute is directly violated, and notably not the veracity and justice of God. Moreover, through a defect of the companion of judgment, the principal end of an oath, namely, the confirmation of the truth spoken, is not lost. "Hence," St. Thomas⁶⁰⁸ says, "it is not necessary that swearing without cause always be a mortal sin, as is swearing falsely." But accidentally an oath made without judgment can be a mortal sin, e.g., because of grave scandal caused, as if a priest should swear in this way, or because of a proximate danger of perjuring oneself.

⁶⁰⁸ 3, dist. 39, q. 1, a. 5, sol. 1 ad 3.

459. Principle 3. An oath pronounced with a defect of justice is from its genus a grave sin.

Enough has already been said concerning this matter above in n. 445; hence it is to be recalled briefly: a) An assertory oath made against justice is a grave sin if the assertion itself was gravely sinful; otherwise it is a light sin, namely, when the assertion itself was lightly sinful.⁶⁰⁹ Hence one who confirms a grave unjust detraction by oath commits two mortal sins, namely, detraction and abuse of an oath. But one who confirms a lightly evil detraction by oath commits two light sins: one of light detraction, the other of light abuse of an oath. b) A promissory oath made without justice, i.e., containing an unlawful promise, is certainly a grave sin if the thing promised is gravely unlawful, e.g., adultery, an irreligious marriage, etc. But if the thing promised is in itself lightly evil, e.g., a lie, slight harm, etc., nevertheless, according to the more probable opinion, such an abuse of an oath seems to be so irreverent toward God as to constitute a mortal sin. Hence one who swears that he will commit adultery commits two mortal sins, namely, against chastity and against religion. But one who swears that he will inflict slight harm upon his neighbor commits one light sin, namely, the slight harm intended, and another probably grave sin, namely, the grave abuse of an oath.⁶¹⁰ Thus objectively speaking. In practice, however, judgment must often be otherwise, both because of a defect of a true intention of swearing and because of the erroneous conscience of the one swearing.

⁶⁰⁹ There are those who teach (e.g., Noldin, De praec. n. 255) that an assertory oath which lacks justice is always a venial sin from its genus.

⁶¹⁰ Cf. Ballerini in the notes to Gury (Comp. theol. mor. I, n. 309), who endeavors well to reconcile the diverse authors apparently disagreeing on this matter.