Chapter II. On the Promissory Oath Specifically

I. Notion. A promissory oath, as we have said (n. 682), is the invocation of God to give assurance concerning one's own future action. In an oath of this kind, as likewise we have already noted, God is invoked: 1. as witness of the present will to place the action; 2. quite probably as patron of the future execution, that is, God is invoked so that He may give authority and force to the proposal or promise; "which," Suarez says, "I explain by a human example. For men are often accustomed to promise, or to make a compromise, or to enter betrothals, before a king or another man of great authority, not so that he should properly be a surety undergoing an obligation, nor even so that he should be witness of the future execution, but so that he may furnish authority to the contract, and so that the contracting parties may understand that they will do injury to him if they do not fulfill the promises."¹ These things also are held by St. Alphonsus as sufficiently founded (III, 173).

Others judge that God in a promissory oath is invoked as witness of future truth, and they appeal to the natural meaning of the words by which the said oath is expressed. Suarez tries to weaken this opinion with these words: "With respect to a future fact He cannot be brought in as witness, for testimony is not given concerning a thing not yet done. And although future things are present to God, nevertheless, insofar as divine testimony is invoked through an oath, there is not asked from God, so to speak, 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 that word except insofar as it is capable of truth when it is spoken; therefore, with respect to a future fact, as to be confirmed by that word, God is not invoked as witness, but as surety, to whose honor and authority it pertains that he who has sworn should effectively accomplish what he has asserted or promised."²

According to others, God is invoked as surety (properly so called), that is, in such a way that He, as it were, promises or proposes together with the one swearing. But that is not proved, so that God, as regards practice or obligation, can be held as only patron of the future execution (n. 689). Nor is a surety properly so called understood by Suarez, as is clear from the words cited.

As to the opinion of St. Thomas, II-II, q. 89, aa. 1, 7, and 9 should be compared.

¹ De iuramento, bk. 3, c. 16, n. 10.

² Cited place.

II. Division. A promissory oath is divided into a simple promissory oath, or one standing by itself, and a confirmatory promissory oath. A simple oath is one which is emitted without a promise (or any obligation), whether previously existing or made together with the oath. A confirmatory oath is one emitted in confirmation of a promise (or of any obligation), whether previously existing or made together with the oath, either to God (a sworn vow), or to man (a sworn promise), or to God and man (a vow sworn together with a promise). Therefore the matter of a simple promissory oath is future action as such; but the matter of a confirmatory oath is the future fulfillment of a promise or of any obligation.

III. Requisites for validity. For validity some things are required on the part of the one swearing, others on the part of the matter.

1. On the part of the one swearing, almost the same things are required as on the part of the one vowing for the validity of a vow (n. 642). It suffices to add these things:

a) For the validity of a confirmatory oath there is required either a pre-existing obligation, or the intention of actually promising something either to God (a vow) or to man. For the validity of an oath standing by itself these things are not required.

It is disputed whether or not for a promissory oath there is necessarily required an intention of obliging oneself by force of the oath. But it seems this must be denied, because for the substance of a promissory oath there is required only the intention of invoking God to give assurance concerning one's own future action (n. 682), not however the intention of obliging oneself by force of that invocation, although that obligation follows as a necessary effect.

b) Fear does not obstruct validity according to these words of can. 1317, § 2: "An oath extorted by force or grave fear is valid, but can be relaxed by an ecclesiastical superior" (St. Thomas, II-II, q. 89, a. 7, ad 3; St. Alphonsus, III, 174).

2. On the part of the matter it is required that it be honorable, not illicit or idle. The reason is that divine authority cannot be the bond of an inequitable or vain thing (St. Thomas, II-II, q. 89, a. 3, and a. 9, ad 3; St. Alphonsus, III, 176).

Corollary I. Oaths of parents to punish their children are commonly invalid or at least do not oblige, either because they were about a useless matter, or rather about disordered vengeance, or because the delinquents have already been corrected or have promised amendment (St. Alphonsus, III, 186). Likewise oaths of merchants not to sell for less or not to buy for more, even if they are made seriously, commonly do not have force, because ordinarily they are about a useless matter.

Corollary II. An oath of fidelity to a political Constitution which contains some things contrary to divine or ecclesiastical law is valid insofar as it is restricted to licit things. It is licit if that restriction is expressly added (namely by adding these or similar words: "saving divine and ecclesiastical laws"), or, as happens today, is drawn from usage.¹ Likewise valid and licit is an oath of fidelity to a usurping Prince, when he peacefully possesses the kingdom (St. Alphonsus, I, 94; II, 74).

Corollary III. An oath emitted by a cleric to remain in the diocese and not to enter Religion is valid, because it regards a thing owed by force of the promise made together with the oath, and confirmed by the oath itself.

Corollary IV. An oath concerning matter partly impossible or inept has force and obliges as to the other part, if the matter is divisible by its nature and also intended divisively. Hence, for example, a prodigal sworn promise (or not sworn) can have force in part.

¹ Cf. Brief of Pius VI Charitas, April 13, 1791; Sacred Penitentiary, December 1, 1866 (Acta Sanctae Sedis 1866, p. 675).

IV. Effects. 1. An oath added to an invalid act (for example, to a contract, promise, or vow) does not render it valid; nor, added to a rescindable act, does it render it unrescindable; since an oath does not change the nature of the contract, promise, or vow, as that exists of itself or by law. To this refer these words of can. 1318, § 2: "But if an oath is added to an act directly tending to the harm of others, or to the prejudice of the public good or of eternal salvation, the act obtains no firmness from this."

2. An oath added to an invalid act does not induce an obligation, because an oath added to an act follows the nature and conditions of the act to which it is added (can. 1318, § 1), or because the accessory follows the principal (St. Alphonsus, III, 180).¹

3. An oath added to a valid act, and likewise an oath standing by itself, induce an obligation, as is clear both from Sacred Scripture,² and from what is soon to be said about the quality of the obligation. Nevertheless, an oath added to a valid act begins and ceases to oblige with the act to which it is added; for, as was said, it follows the nature and conditions of this act. But more must be said about the obligation of a promissory oath. Moreover:

a) A promissory oath induces an obligation of religion (can. 1317, § 1). The reason is that the reverence owed to God demands that the action be placed in the case in which God has been invoked as patron of the execution, as happens in a promissory oath. But the obligation of an oath differs in species from the obligation of a vow, because the former regards God as witness of the present will and patron of the future execution; the latter regards Him as creditor.

Corollary. He who violates a promissory oath perpetrates at least two sins: namely, against the obligation of religion induced by the oath, and against the obligation, whether of religion induced by a vow, or of another virtue, induced by a promise made to man. A third is added, if he violates an oath added to a vow with a promise made to man.

b) A promissory oath induces a grave obligation of religion, if it regards a grave matter; for it is grave irreverence to omit a grave act as to which God has been invoked as patron. If it regards a light matter, it is disputed whether the obligation is grave or light. But it is quite probably only light, because grave irreverence does not appear in the fact that an action of lesser moment is omitted, even if God has been invoked as its patron (St. Alphonsus, III).³

Nevertheless note that he sins gravely who, while he swears, does not have the will of standing by the promises; because in a promissory oath God is invoked as witness of the present will. But it is grave irreverence to invoke God as witness of what is false.

c) As to establishing the extension of the obligation, the following rules have force:

a) An oath must be interpreted strictly according to law and according to the intention of the one swearing, or, if he acts with deceit, according to the intention of him to whom it is sworn (can. 1321).

b) A confirmatory oath follows the nature and conditions of the act to which it is added (can. 1318, § 1). Therefore its obligation extends itself to the same things to which the act - for example, a vow or promise - in confirmation of which it is added, extends.

Corollary. An oath which regards matter of law obliges according to the limits of law. Hence, for example, a pastor who has sworn residence can be non-resident insofar as this is conceded by law. An oath of observing statutes or rules does not oblige as to rules abrogated by legitimate desuetude; furthermore, an oath of this kind obliges under grave obligation or under light obligation or to penalty alone, according as the statutes themselves of themselves oblige under grave obligation, or under light obligation, or to penalty alone (St. Alphonsus, III, 181).

¹ Nevertheless, it is not repugnant that an oath added to an invalid act induce an obligation; for strictly speaking someone can oblige himself independently of the value of the act to which the oath is added. But these things are almost hypothetical.

² Matt. 5:33.

³ Those who teach that God in a promissory oath is invoked either as witness or as surety of the future action rightly conclude that the obligation of the aforesaid oath is always grave: for it is grave irreverence to constitute God a false witness or an unfaithful or changeable surety. But the antecedent is not proved.

V. Cessation. From can. 1319, a promissory oath, or the obligation induced by an oath of this kind, ceases:

1. If it is remitted by him for whose advantage the oath had been emitted (St. Thomas, II-II, q. 89, a. 9, ad 2; St. Alphonsus, III, 193). And that remission quite probably is made validly and licitly even when the oath was emitted principally in honor of God. "The reason is that, although the promise was made to God, it was nevertheless always made dependently on the will of the man to whom it was sworn, namely: if he does not remit the execution" (St. Alphonsus, cited place).

2. If the thing sworn is changed substantially; or, when the circumstances have changed, becomes either evil or altogether indifferent; or finally impedes a greater good. The former is drawn from the fact that the intention of the one swearing is not judged to have extended itself to matter substantially or notably changed, as was said concerning the intention of the one vowing (n. 653). The other things follow from this: that the thing sworn, if it becomes evil, or indifferent, or an impediment to a greater good, ceases to be matter apt for an oath (n. 688). Notice, however, that honorable matter promised and accepted in favor of a third party, even if perhaps less perfect in itself, nevertheless here and now remains more perfect, indeed is commanded, on account of the right acquired by the third party (n. 688).

3. If the final cause or the condition under which perhaps the oath was given is lacking. See what was said about a vow, n. 655.

4. By irritation, dispensation, or commutation, according to the norm of can. 1320. Moreover, from the cited canon:

a) The same persons who can irritate vows can irritate promissory oaths, and for the same reason (n. 662). They can irritate them - equally as vows - even if the irritation tends to the prejudice of others, even though these refuse to remit the obligation.

b) Likewise the same persons who can dispense or commute vows can dispense or commute promissory oaths, and for the same reason (n. 671); but if the dispensation of the oath tends to the prejudice of others, the Apostolic See alone can dispense or commute the oath on account of the necessity or utility of the Church (St. Alphonsus, III, 189, 192).