§ 1. On the Notion and Division of an Oath

437. Definition. An oath (which is sometimes also called a swearing and a sacrament) can be defined: an invocation of the divine Name as witness to veracity. Hence St. Thomas⁵⁰⁸ says: "To take God as witness is called swearing."

The definition given is explained. It is said, first: an invocation of the divine name, insofar as man, inwardly conscious of the defect of his own veracity and knowledge, invokes as an aid God, the first truth in knowing and speaking. Hence every true oath is a true worship of God, and presupposes faith in the existence of a personal, omniscient, and omnipotent God, who knows every lie and punishes it. Therefore the oaths of atheists, pantheists, monists, materialists, etc., and generally of all who deny the existence of a personal God, are not true oaths. Therefore not even a judge can demand an oath from them; he can, however, certainly compel them under grave penalties to tell the truth. Certain jurists call this obligation of telling the truth imposed by a judge a civil oath, in opposition to a religious oath; but this distinction is to be rejected, since every true oath is essentially an act of religion. Since today so many men openly profess crude atheism, it has more than once already been proposed that the oath be abolished in civil tribunals. The invocation of the divine name in an oath can be either express or tacit through signs, e.g., through touching the Gospel, through raising the fingers, etc.

It is said, second: as witness to veracity. For the end of every oath is the confirmation of the truth spoken. But since the truth of contingent facts cannot be proved from intrinsic causes, it must be sought elsewhere, namely, through the testimony of men. This testimony of men, however, is often insufficient and fallacious because of a defect both of knowledge and of veracity. Therefore it is necessary to have recourse to the testimony of God, who can neither be deceived nor deceive.⁵⁰⁹ Nevertheless, the one swearing neither intends nor asks that God here and now testify to the truth by an actual and clear sign, for this would be a tempting of God, but that the omniscient, just, and omnipotent God testify to the truth how and when it shall please Him, and punish the one swearing falsely most gravely.⁵¹⁰

⁵⁰⁸ S. theol. 2, 2, q. 89, a. 1. Aristotle (Pseudo-Aristotle) defines an oath: "Ὅρκος δ' ἐστὶ μετὰ θείας παραλήψεως φάσις ἀναπόδεικτος" -- "An oath is an assertion with an invocation of the gods, admitting of no proof" (Rhet. ad Alexand. c. 17). Also excellent is the definition given by the distinguished Göpfert: "The oath is the express or tacit invocation of God as witness of the truth, either for the confirmation of a statement or for the strengthening of a promise" (Der Eid [1883], 152), or in Latin: An oath is the invocation of the divine name in testimony, to establish faith in a statement or to confirm a promise.

⁵⁰⁹ S. theol. 2, 2, q. 89, a. 1.

⁵¹⁰ Cf. ib., n. 2 ad 3.

438. Divisions of an oath. Among the several divisions of an oath, let it suffice to enumerate the following, which are necessary for a confessor to know:

1. By reason of the object or matter, an oath is distinguished into assertory and promissory.⁵¹¹ In an assertory oath God is invoked as witness to a past or present truth; e.g., I swear that I did not commit that crime; or I swear that I am incapable of paying.⁵¹² In a promissory oath God is invoked as witness both to a future event and to the present sincere intention of doing or omitting something; e.g., I swear that I shall fulfill all the duties of my new state.⁵¹³ A promissory oath, therefore, confirms the present sincere will and binds it lest it be changed in the future. The Angelic Doctor⁵¹⁴ explains both oaths in this way: "Divine testimony is sometimes introduced to assert present or past things, and this is called an assertory oath. But sometimes divine testimony is introduced to confirm something future, and this is called a promissory oath." If anyone considers a promissory oath accurately, he will find that it always includes an assertory oath; for one who swears that he will do something invokes God as witness to a certain present truth, namely, that he now has the intention of effecting that which he promises. Then he invokes God as guarantor of the future truth, namely, that he will fulfill the thing promised. Nevertheless, the division of an oath into assertory and promissory is not therefore superfluous; for although a promissory oath includes an assertory oath, the converse does not hold.

A promissory oath is customarily subdivided into a sworn resolution, a sworn promise or sworn pact, a sworn vow, and a vow with a sworn pact. a) A sworn resolution (which is also called a simple promissory oath) is a resolution, confirmed by an oath, of doing or omitting something; e.g., I swear that I shall no longer play cards. b) A sworn promise is a promise made to a man and confirmed by an oath; e.g., I promise you marriage and swear that I shall fulfill the betrothal thus contracted. Since this promise is a contract or pact, such an oath is also called a sworn pact. c) A sworn vow exists if a promise is made not to a man but to God and is confirmed by an oath. d) Finally, a vow can be made for the benefit of some third person and accepted by him. If an oath is added to such a vow, there is then a vow with a sworn pact.

2. By reason of form, an oath is distinguished into invocatory and execratory (imprecatory).⁵¹⁵ The first simply invokes God as witness to the truth, and therefore is also customarily called a contestatory oath; e.g., I swear by God that the matter is so. The other invokes God not only as witness to the truth, but also as avenger of falsehood. The one swearing can imprecate vengeance for falsehood upon himself in three ways: a) directly from God Himself; e.g., May God destroy me, may He punish me, if I have not spoken the truth. In Sacred Scripture the words, "May God do these things to me and add these things," are often used as the formula of an oath of this kind.⁵¹⁶ In canon law the formula now in force is: "So may God help me and these holy Gospels of God"; its meaning is: May God no longer help me if I pronounce what is false. b) Through creatures, God so permitting; e.g., May lightning kill me, may the devil seize me, may the earth swallow me, etc., if I do not speak the truth. David uttered an oath of this kind, saying: "If I have rendered evil to those who repaid me, let me deservedly fall empty before my enemies."⁵¹⁷ c) Through persons intimately joined to him, who are to suffer harm; e.g., a father swears by the head of his son; its meaning is: Let my dearest son be punished capitally if I lie.

3. By reason of manner, an oath is distinguished into solemn, which is made with a certain solemnity, e.g., with candles lit, before a crucifix, with the Gospels touched, etc., and simple, which is pronounced privately, without these solemnities, in whatever words are preferred. A solemn oath can be made not only by words but also by gestures, e.g., by touching the Gospel, kissing the Bible, etc. Since a solemn oath is always employed in trials, it is also called a judicial oath. But an extrajudicial oath is every other oath, whether it is in solemn form or in simple form. A judicial oath has very many subdivisions, e.g., an oath against calumny, an oath against malice, a supplementary oath, an oath tendered, etc., which we omit here because knowledge of them pertains not to Moral Theology but to either ecclesiastical or civil law. For all oaths are of the same moral species because they all agree in the invocation of the divine name, although they differ accidentally.

4. By reason of invocation, an oath is distinguished into explicit and implicit. The first is that by which God Himself is explicitly and immediately invoked as witness, e.g., God is my witness. The other is that by which a creature is indeed immediately invoked, but God Himself mediately, because in such a creature a special relation to God shines forth. Thus Moses swore implicitly, saying: "I call heaven and earth as witnesses today that I have set before you life and death, blessing and cursing."⁵¹⁸

⁵¹¹ In German: Aussage- and Zusageeid [assertory oath and promissory oath].

⁵¹² Offenbarungseid [oath of disclosure].

⁵¹³ Amts- or Diensteid [oath of office or service].

⁵¹⁴ S. theol., l.c., a. 1.

⁵¹⁵ Zeugnis- and Verwünschungseid [testimonial oath and imprecatory oath]. Cf. S. theol. 2, 2, q. 89, a. 1 ad 3.

⁵¹⁶ Cf. 1 Kings 14:44; 2 Kings 3:35.

⁵¹⁷ Ps. 7:5.

⁵¹⁸ Deut. 30:19.