Chapter 1. On the Oath Generally

I. Notion. An oath is the invocation of God, or of the divine Name, to give assurance concerning some matter. It is called:

1. An invocation. Therefore it is not enough that someone merely assert, for example, that he speaks before God, or that God knows or testifies to the truth of the matter affirmed by him. If, however, the aforesaid things are uttered not only enunciatively, but invocatively, as the Apostle did,¹ there is a true oath.

2. Of God; not of a man; nor of an Angel or Saint, if one stops at their testimony. But we swear by God alone, because He, as very truth and very veracity, can neither be deceived nor deceive, and therefore He is able to procure full credibility for what is said.

3. To give assurance concerning some matter, that is, either concerning the truth of one's assertion, or concerning one's own future action. To give assurance concerning the truth of an assertion, God is invoked as witness of the assertion; and there is an assertory oath. To give assurance concerning one's own future action, God is invoked as witness of the present will to do something, and as patron of the future execution; and there is a promissory oath. I said: that God is invoked as witness, namely so that by His testimony He may confirm what is asserted, not however that He should perform this here and now, but at the time and in the manner which shall have pleased Him, at least "when He will bring to light the hidden things of darkness and will make manifest the counsels of hearts"² (cf. St. Thomas, II-II, q. 89, a. 1; St. Alphonsus, III, 133).

Corollary I. For the essence of an oath there is required the intention or will of invoking the authority of God, so that it is not enough to use only words which signify invocation. For human acts do not operate beyond the will of the agent; wherefore, if the intention or will of invoking God is absent, there is not a true invocation of God, but only the external signification of invocation (St. Alphonsus, III, 133).

Corollary II. For the essence of an oath, according to many, a merely internal invocation suffices. Whatever the case may be, certainly an oath of this kind, merely mental, must be called incomplete, insofar as such an invocation is not apt to give assurance (before men) concerning some matter. In order that this be obtained, the invocation of God must be externally expressed. But as to the said expression, or as to the formulas of an oath, note:

a) It is the same: 1. whether the expression is made by words or by gesture or deed, as if, when asked whether you swear, you nod your head; or you touch the book of the Gospels offered for swearing; or you subscribe to an oath-formula; 2. whether the expression is determined to an invocation of God of itself or from the circumstances (St. Alphonsus, III, 134, 136).

b) Among expressions or formulas, some of themselves are certainly oath-formulas, others are ambiguous, and others are not oath-formulas. Certainly oath-formulas are, for example: "I call God to witness"; "let God be witness for me"; "I swear by God," etc.

Ambiguous are: "I swear"; "I speak before God"; "God is witness for me," etc. To judge whether or not they involve an oath, the circumstances and the intention of the speaker should be inspected. Thus if someone responds to a request for an oath, "I swear," the oath subsists.

Not oath-formulas are, for example: "in truth"; "by my faith"; "by my honor"; "it is as true as God is," etc. (St. Alphonsus, III, 134-138, 143). Nor are formulas oath-formulas which, because of circumstances, lose the signification of an invocation, as if they are uttered in a school or in a theater, for the sake of teaching or representation.

¹ Gal. 1:20: "Behold, before God, that I do not lie."

² 1 Cor. 4:5.

II. Division. An oath is divided chiefly:

1. Into explicit and implicit, according as God is invoked directly or indirectly, namely through creatures in which His attributes specially shine forth. Such are, for example, the Saints, heaven, the Church, the sacraments, the Cross, the soul; such are not, for example, trees, a beard, etc.

2. Into assertory and promissory, according as God is invoked to give assurance concerning the truth of an assertion, or concerning one's own future action.

3. Into execratory and non-execratory. An execratory oath is one by which God is also invoked as avenger of perjury or of broken faith, if these take place.¹

4. Into solemn and simple, according as it is emitted with a special ceremony or without it (St. Alphonsus, III, 140, 141).

¹ The sense of the formula "So may God help me and these holy Gospels of God" is: If what I swear is true, may God help me; may He not help me, if it is false.

III. Morality. An oath, with the due conditions observed, is an honorable act, and one of religion. It is an honorable act, as is clear from Sacred Scripture, which approves the oath both directly,¹ and indirectly by exhibiting oaths emitted under divine inspiration.² It is an act of religion, because it honors the authority of God, who is invoked to give assurance concerning some matter (St. Thomas, II-II, q. 89, a. 2; St. Alphonsus, III, 144).³

¹ Deut. 6:13; 10:20; Ps. 15:1, 5, etc.

² Rom. 1:9; 2 Cor. 1:23; Gal. 1:20, etc.

³ Objection. Christ in Matt. 5:33 says: "You have heard that it was said to the ancients: You shall not swear falsely, but you shall render your oaths to the Lord. But I say to you: do not swear at all, neither by heaven... nor by earth... But let your speech be: yes, yes; no, no; and whatever is more abundant than these is from evil." The same is in St. James 5:12. Response with St. Augustine: "The Apostle himself swore in his letters, and thus showed how what was said should be understood, I say to you, do not swear at all, namely lest by swearing one come to facility in swearing, from facility to custom, and so from custom fall into perjury. And therefore he is not found to have sworn except while writing, where more cautious consideration does not have a headlong tongue. And this indeed is from evil, as it was said, whatever is more is from evil: not however from his own evil, but from the weakness of those to whom he was striving to give assurance even in this way" (De mendacio, c. 15).

IV. Required conditions. For the liceity of an oath three things are required: truth, judgment, and justice (can. 1316, § 1; St. Thomas, II-II, q. 89, a. 3).²

1. Truth; by which here is understood the certainty of the one swearing concerning the truth of his own assertion. In court, strict moral certainty is required; for this is intended by the judge. Outside court, moral certainty taken somewhat more broadly suffices (St. Alphonsus, VI, 148). Moreover:

a) Defect of truth is a grave sin from its whole genus; since he inflicts a grave injury upon God who invokes Him as witness of an assertion which he holds as certainly or probably false. There is added proposition 24, condemned by Innocent XI: "To call God as witness of a slight lie is not such great irreverence that on account of it He would wish, or could, damn a man."³ A sin committed in this way is called perjury.

b) An oath emitted with a mental restriction:

a) It is illicit, indeed perjury, if the restriction is purely mental. For a restriction of this kind involves a lie, so that in the given case God is invoked as witness of a matter which is held as false. There is added proposition 26, condemned by Innocent XI: "If someone, either alone or before others, whether questioned or of his own accord, whether for the sake of recreation or for any other end, swears that he has not done something which he truly has done, understanding within himself something else which he has not done, or even another way than that in which he did it, or any other true addition, he really does not lie and is not perjured";⁴ cf. also proposition 27.⁵

b) It is licit, provided a just cause is present, if the restriction is not purely mental, because a lie is absent, and therefore God is not invoked as witness of what is false. For the same reason it is only venial to swear in this way without a just cause. But it is prohibited under grave obligation to swear, even with a restriction not purely mental: 1. in court, where someone is legitimately questioned; 2. in contracts (St. Alphonsus, III, 151, 152).

2. Judgment requires that one not swear without necessity or utility. Namely, although an oath is an act of virtue, that is, of religion, nevertheless that act is not the primary end of an oath; the primary end is the confirmation of truth for man's utility; hence for the liceity of an oath necessity or utility is required.

Defect of judgment of itself is only venial, because grave irreverence does not appear in it (St. Alphonsus, III, 144, 145).

3. Justice requires: 1. in an assertory oath, that the assertion itself be licit; 2. in a promissory oath, that what is proposed or promised be honorable. Hence, for example, justice is lacking in an oath by which someone confirms a sinful detraction, or by which he swears that he is going to commit an injustice (St. Alphonsus, III, 146).

Defect of justice is a grave or light sin according as the assertion, proposal, or promise which is confirmed by oath is gravely or lightly illicit. Hence:

a) He sins gravely who by an assertory oath confirms a gravely evil assertion, and thus promotes a grave evil effect; as if someone were to confirm by oath a gravely injurious detraction: thus, namely, he would promote grave infamy of his neighbor. The reason is that it is grave irreverence to abuse divine authority in order to promote a grave evil effect. Otherwise, it is quite probably only a light sin, namely, if someone were to confirm by oath a lightly evil assertion, or were to confirm an assertion indeed gravely evil - for example, boasting about a sin committed - but by the oath would bring about this one thing, that others would be made more certain about the assertion, without a grave evil effect being promoted from it (St. Alphonsus, III, 146).

b) Likewise he sins gravely who deliberately uses an oath (whether assertory or promissory) as a means to grave sin; as if someone were to swear that the master is absent, in order to induce someone to a grave injustice. But to use an oath as a means to a light sin quite probably does not of itself exceed the venial.

c) Moreover, he sins gravely who emits a promissory oath concerning a gravely illicit matter; if concerning a lightly illicit matter, it is disputed whether it is a grave or a light sin. St. Alphonsus (III, 146) deservedly holds as more probable that it is a grave sin, because grave irreverence seems to be present in the fact that God is constituted patron of a future action, even though only lightly evil. An oath against the evangelical counsels is held by the holy Doctor to be venial (St. Alphonsus, cited place).

d) Finally, the custom of swearing without due attention to truth or justice is gravely sinful, because he who acts in this way exposes himself to the grave danger of oaths destitute of truth and justice. There is added, as to the custom of easily emitting promissory oaths, the danger of not fulfilling them (St. Alphonsus, III, 145).

¹ Cf. Gopfert, Der Eid.

² Jer. 4:2.

³ Denzinger-Bannwart, n. 1174.

⁴ Denzinger-Bannwart, n. 1176.

⁵ Denzinger-Bannwart, n. 1177.