2245. Oaths.—An oath is the calling upon God to witness the truth of what we say.
(a) It is a calling upon God; that is, it is the selection of God as the witness of what is said. The oath is not merely an address made to others or a declaration that a fact is known to God (e.g., “God knows she has been a good woman”); it is an address or invocation made to God Himself. Neither is it a mere prayer that God will in some way bring out the truthfulness of what is said; it is an appeal to Him to corroborate that truthfulness by His own testimony. Neither does it appeal to testimony already given (e.g., the words of God found in Sacred Scripture), but to testimony to be given about the present matter. A prayer to God to prove one’s innocence or the proof of a theological proposition from the Word of God is not, therefore, an oath.
(b) It is a calling on God, and hence if appeal is made to some creature (e.g., in the expression, “upon my word of honor”) or to some false deity (e.g., “By Jove, I’ll do that”), there is no oath.
(c) It calls on God to bear witness; that is, it confirms the truth of one’s words by God Himself, who can neither deceive nor be deceived. He who swears does not ask that God intervene here and now by some visible or miraculous sign, but that God confirm, where and when it pleases Him, what is said, at least on that day when He will clear up the hidden things of darkness and reveal the secrets of hearts (I Cor., iv. 5). The proving force of the oath is that one who believes in God will not be so wicked or rash as to call upon the All-Holy to defend iniquity and falsehood.
2246. The Various Kinds of Oaths.—(a) By reason of the matter, an oath is either assertory or promissory. An assertory oath refers to the past or present (e.g,, “I swear that I saw the accident,” “I swear that I am insolvent”), a promissory oath to the future (e.g., “I swear that I will execute my office faithfully”). The promissory oath is either without a pact made with another (e.g., in the comminatory oath, “I swear that I will prosecute, if you do that”) or with a pact. This latter oath is called confirmatory, and, according as the pact is with God or with man or with both, it is either a sworn vow, or a sworn contract, or a sworn vow and contract.
(b) By reason of its mode, an oath is either contestatory (invocatory) or execratory. The contestatory oath simply calls on God as a witness (e.g., “God is my witness that this is true,” “I swear by God, etc.”). The execratory oath asks God, even though the Divine Name is not expressly mentioned, to punish the swearer in his own person or in the persons or goods that pertain to him, if the statement made is not true (e.g., “May God strike me dead, if this is not true!” “May the devil take my children, if I swear falsely!”). The form commonly used, “So help me God and these holy Gospels!” has an execratory sense, the meaning being “May God help me if I speak truly, may He deny me help if I speak falsely!”
(c) By reason of the person invoked, an oath is either explicit or implicit. The former calls on God by name (e.g., “God is my witness,” “I speak the truth in Christ”); the latter calls on some creature as the reflection of a divine attribute, or in some other way the representative of God (e.g., the oath of Moses in Deut., xxx. 19: “I call upon heaven and earth this day to witness that I have offered you life and death”).
(d) By reason of its legal form, an oath is either solemn or simple, judicial or extra-judicial. The solemn oath is taken with ceremony (e.g., before the altar, with hand placed on the Bible, with upraised hand, etc.); the simple oath is taken privately, without special form of words or ceremony. The judicial oath is taken in court or in reference to the public decision of questions of right, fact or delinquency (e.g., in Canon Law the oaths of calumny, malice, etc., which are treated in canonical works); the extra-judicial oath, solemn or simple, is taken on other occasions (e.g., when two contractants strengthen their compact by oath). Examples of solemn oaths in the Bible are found in Gen., xiv. 22, xxiv. 2, 3; Jeremias, xxxiv. 18.
2247. Moral Difference between the Various Kinds of Oaths.—(a) Essentially, there is no difference, since all the kinds agree in the principal features mentioned in the definition. (b) Accidentally, there is a difference in circumstances of form, solemnity, etc. Moreover, one kind of oath may be more obligatory (e.g., the solemn oath on account of the special deliberation given it and the scandal caused by its non-observance is more sacred than the simple oath), or it may have other species of obligation besides that of religion (e.g., the oath to keep a compact binds in justice as well as religion).
2248. Lawfulness of Oaths.—(a) It is lawful to take an oath that has the necessary qualities, for in Scripture God Himself is represented as swearing (Gen, xxii. 16; Psalm cix. 4, Heb., vi. 13, vii. 21), holy men swear and are praised for swearing as they should (II Cor., i. 23; Psalm xiv. 4), and the Church has always made use of oaths. The origin of oaths is man’s faith in God, and their purpose is the useful one of lending authority to important assertions. Indeed, an oath is an act of religion, for men swear only by one who is greater (Heb., vi. 13), and hence an oath is a profession of reverence for God’s superior knowledge, truth, and justice.