Article — Merkelbach, Summa Theologiae Moralis
Article I: On the Essence and Object of an Oath
S. Th. II-II, q. 89, a. 1, 4, 6.
742. Oath (serment; eed) is said from right, because it was introduced for right or law, among all nations, so that what is said under invocation of divine testimony may be held as true; therefore to swear (eed doen of zweren) is to appeal to God as witness of some matter, or, as St. Thomas says, a. 1, "to assume God as witness." Whence oath is defined: Invocation of divine testimony, or with the Code (can. 1316): "the invocation of the divine Name as witness of truth."
Therefore the end of an oath is the confirmation of truth. Confirmation in the sciences is made through reason, which proceeds from evident things to conclusions; there witnesses and oath are not employed: for one would seem ridiculous if, in the disputation of some science, he wished to prove what was proposed by an oath. But the particular and contingent facts of men cannot be confirmed through reason (from intrinsic causes), and therefore they are accustomed to be confirmed through witnesses. Human testimony, however, is not always sufficient for confirming these things, on account of defect of veracity or knowledge, and therefore it was necessary to have recourse to divine testimony, because God can neither lie nor be ignorant of anything (a. 1).
But one swearing does not ask that God here and now testify to the truth of the statement by an actual sign (for that would commonly be tempting God), but when and how it pleases Him, at least in the future judgment (a. 2, ad 3), or that He punish most gravely one swearing falsely (a. 1, ad 3). And yet the invocation serves to produce faith immediately among men, because someone is not easily judged to be of such impiety and boldness that he would make God a witness of falsehood and subject himself to divine vengeance.
743. An oath is an invocation; therefore it is an act of reason: an interior speech, which nevertheless presupposes an act of the will, namely, at least the implicit intention of swearing and of calling God as witness.
Hence an oath is not:
a) An invocation pronounced indeliberately by him who does not know what an oath is, or by him who is ignorant of the sense of the words or does not advert sufficiently: an unconscious oath.
b) Nor an invocation pronounced merely materially in circumstances which exclude every intention of invocation, for example, if it is made in school or in a theater for the sake of teaching or representing, or by way of interjection as in common speech, by God (for example, par Dieu, c'est vrai): a narrated oath.
c) Nor a deliberate but merely external invocation without intention: a fictitious oath, for example, by him who does not admit the existence of God.
For a human act does not operate beyond the intention of the agent. But an oath must be a human act, not only insofar as it is speech, but also insofar as it is an invocation of God as witness: for invocation can be made for a diverse end. Therefore, in order that it be made for a witness, the intention of uttering words and expressing an invocation of divine testimony does not suffice, but the will of invoking God as witness is required. A fictitious oath is an irreligious lie, of itself venial, sometimes mortal because of grave public or private harm, as in judgments and contracts.1
1 Hence condemned by Innocent XI is proposition 25: "With cause it is licit to swear without the mind of swearing, whether the matter is light or grave."
A merely internal oath, although it is valid before God, as if someone invokes Him internally as witness that he wishes firmly to avoid sin, nevertheless does not obtain its effect of confirming assertions and promises before men, whence it is incomplete; likewise if someone, intending to swear, uses a formula wholly unfit for this. Therefore, in order that an oath be complete, it must be expressed by some oath formula; and therefore on the part of the mode by which the invocation is expressed, it is divided into verbal, real, and mixed, according as it is expressed either by words or by signs (the raising of fingers, the touching of a scepter, cross, or gospels), or by both.
744. An oath is the invocation of testimony or an appeal as witness of truth.
Hence a) it is not the invocation of the merciful and omnipotent God by way of prayer and supplication for obtaining some good, favor, or help, even, for example, for showing truth or conciliating faith for ourselves; but it is the invocation of the infinitely true God for obtaining testimony for confirmation, by which, insofar as it is in us, we constitute Him witness, that is, we cite Him and consent that He be witness, if He wills.
b) Nor is it the invocation of Sacred Scripture to confirm doctrine: for it is one thing to use testimony already given, another to invoke the testimony of God as to be exhibited (a. 1, ad 1).
c) Nor is it a simple assertion of divine omniscience, as in the expressions: I speak before God; God hears me; He knows that I speak the truth; God is witness; God will testify in His own time; God is truth; the Lord lives; the Lord sees my conscience, etc.; unless they are pronounced not only narratively and enunciatively, but invocatively, as the Apostle, Gal. I, 20: Behold before God, that I do not lie...
d) Nor is it a simple comparison of the asserted truth with an evident truth, for example, it is as true as God exists, as the sun shines, as I sit here (as in Dutch waarachtig Gods), or with a truth of faith, for example, it is true as the Gospel, after the likeness of faith, as infallible as the Church: in which case nevertheless ordinarily some irreverence toward God or sacred things will not be lacking.
e) Nor is it a simple vehement affirmation as in the expressions: in truth, by my faith (that is, human faith), in conscience, by my conscience, by the conscience of my soul (for example, ma foi, ma parole d'honneur; op mijn woord).
f) Nor is it a simple wager or obligation of a penalty, for example, if it is false, I pledge my head; I wish to be a thief; let me be a heretic; let my ears be taken off; let me be killed, hanged, die; let the devil take me; ... by damnation, come here, etc.; unless God is invoked as witness of truth and at the same time avenger of falsehood.
On the part of the testimony which is sought, an oath is merely contestatory or directly invocatory (getuigeniseed) if God is invoked only as witness for manifesting truth; or indirectly, namely, execratory or imprecatory (vervloekings- of verwenschingseed) if He is also invoked as avenger for punishing falsehood. This often happens if He is expressly named, for example, if I lie, may God punish me, destroy me, damn me..., or if the evil is commonly regarded as proceeding specially from divine providence, for example, if I lie, may lightning from heaven strike me, may I descend into hell (a. 1, ad 3).
745. An oath is the invocation of divine testimony or of the divine name. Hence he does not swear 1. who does not say whom he invokes, for example, I swear that it is so, unless from the circumstances it is clear that he intends God, for example, if the demand for an oath preceded; nor 2. he who invokes false gods; nor 3. he who appeals to men as witnesses; or 4. even to the saints, stopping at their testimony: for this is nothing but an act of dulia.
Yet a) if a creature is invoked insofar as it belongs and is referred to its Author, and represents His supreme truth and majesty, the Creator who shines forth in creatures is implicitly and mediately invoked, for example, if someone swears by heaven, by the holy faith, by the cross, by the Gospels, by the sacraments, by the temple, by the saints, by relics, or by other nobler creatures which commonly are regarded insofar as they have a special relation to God; but by baser creatures no one is judged to swear, nor would that be licit because of irreverence.
Similarly b) if someone obliges himself or something pertaining to himself to a penalty and offers it to God as avenger of falsehood, there is an execratory oath in which God is implicitly invoked as witness and avenger, for example, I swear by my head, by my son, by my salvation... Such an oath is the expression by my soul (II Cor. I, 23), unless nevertheless, as often happens, the faithful do not advert to the special relation of the soul to God.
On the part of Him by whom one swears, an oath is explicit or immediate, or implicit or mediate (a. 6).
746. Famous is the division of oath into assertory and promissory, which is taken on the part of the object or matter, according as an oath turns upon the assertion or affirmation of the one swearing concerning the present, for example, I think it is so, I am incapable of paying, or concerning the past, for example, I did this, or upon an action or omission to be executed by the one swearing in the future. In the first case it is assertory (bevestigende of bloote eed), in the other promissory (belovende of verbindende eed).
In a promissory oath 1. God is invoked to testify to the present intention of the one swearing to do what he proposes; whence it includes an assertion concerning the present and adds a purpose concerning the future, and therefore when we distinguish an assertory oath from a promissory one, we understand it as merely assertory. 2. Nevertheless God is not invoked as witness of the future execution, for testimony is not given about a thing not yet done;2 nevertheless 3. God is as it were the patron,3 who gives special authority and force to the promise and urges its execution by a special obligation of religion: for just as men promise or enter betrothals before a king, judge, or other man of great authority, who lends authority to the contract, so that they understand that they would do injury to him if they do not fulfill the promises, so also they promise with God invoked; but if they do not fulfill, they inflict injury upon Him. Whence by such an oath God is invoked that He may confirm the present sincere will and bind it lest it be changed in the future.
2 Although future things are present before God, nevertheless by oath there is not asked from God testimony concerning a future thing as it is present to Him, but as it is in the word of the one promising. But in this way testimony does not fall upon the word except insofar as it is capable of truth when it is spoken; therefore with respect to a future deed God is not invoked as witness. Suarez, De Religione, l. I, c. 9, n. 25.
3 Others say surety, but "this word... we cannot take in the strict sense, in which he is called a surety who answers for another so as to take upon himself the burden of paying the promise in defect of another." Dignant, De Virtute religionis, n. 221.
A promissory oath is a) strictly promissory or accessory when the action which is sworn is truly promised, whether to God by vow (a sworn vow), or to man (a sworn deed), or to both (a sworn vow in favor of a third party); or b) broadly promissory or standing of itself when the action is not promised but only proposed, whether for another's honor or favor (an oath confirmatory of a purpose or a sworn purpose), or for penalty or vengeance (a comminatory oath; bedreigingseed).
747. An oath is an act of religion. For nothing is confirmed except by something which is more certain and more excellent; therefore he who invokes divine testimony to confirm what he says, by this very fact professes God to be more excellent, as one whose truth is indefectible and whose knowledge is universal, and thus he exhibits reverence to God. But to reverence God belongs to religion; therefore. Cf. Deut. VI, 13; Ps. LXII, 12; Hebr. VI, 13-16.
All oaths in the account of oath are of the same species, because since the account of oath consists essentially in the invocation of God, all the differences brought forward above, or diverse modes of invocation, are related materially and per accidens to God's testification, and consequently do not change its essence and species.4 - Nevertheless other species can accede, for example, of fidelity, justice, dulia, and if the oath is sinful, of blasphemy, injustice, scandal, etc.
4 Nor is a promissory oath distinguished in species because one thing is to invoke God as witness of present truth, and another as patron of future execution. For in an oath the testimony of God and His authority are not invoked distinctly and separately, but God is invoked as testifying to the present intention and consequently He urges the future execution, because the matter concerns a future thing promised; which returns to a material difference. Dignant, o. c., n. 246.
748. Practical observations. - 1. In doubt concerning the intention of the one swearing, judgment is to be made from the circumstances, for example, whether the demand for an oath preceded, whether the one swearing is accustomed to swear, etc., but especially from the words employed: if the formula from its proper sense and common usage is oath-like, and was pronounced advertently, an oath is presumed; if it is doubtfully oath-like, it is not presumed but must be proved; but if it is ambiguous and the intention is not established, an oath is not judged to be present.