Article Second. On the Conditions Required for an Oath

246. The conditions of a valid oath are two: a. the intention of swearing; b. an oath-formula.

That on the part of the one swearing there are besides required for a valid oath the same conditions which are required for a vow, namely perfect deliberation and perfect liberty, is gathered from the same reason in each case. But on the part of the matter in a promissory oath it is required that it be possible, good or licit, and better than the opposite, as was said above concerning vow.

1. The intention of swearing is required, either formal or at least virtual: for an oath by its nature is an act of the will, namely a petition; but without the intention of petitioning there is no true petition.

a. The value of an oath in conscience depends upon the intention of the one swearing, so that he truly swears who has the mind of swearing, even if the formula which he uses is less suitable; and he certainly does not swear who does not have the mind of swearing, whatever the words or signs may be which he uses. In doubt concerning the intention of swearing, the value of the oath must be judged from the sense which the words used have from common acceptance; therefore if the words from common use are oath-words, he must be judged truly to have sworn; if from common use they are not oath-words, he is presumed not to have sworn; but if the words are ambiguous, likewise no oath is had.

b. He has virtual intention who uses oath-words in their customary sense, even if he does not expressly think of invoking divine testimony. Therefore if one uttering oath-words, whether from ignorance or from inconsideration, does not even implicitly advert to an oath, he makes no oath.

2. An oath-formula is required, by which God is invoked in testimony. For although an internal oath conceived by the mind alone, absolutely speaking, is a true oath,¹ nevertheless, because an oath from its proper end is used for the sake of others, it must be manifested to them by an external sign.

¹ Suarez, l. 1, c. 1, n. 4.

247. Some oath-formulas are certainly oath-formulas; some are ambiguous; some certainly are not oath-formulas.

a. Formulas of explicit oath are: let God be witness to me; I swear by God, by Christ, by the truth of God; may God destroy me, if, etc.; even simply the word I swear suffices, if the intention of swearing is established. Nevertheless, when the intention of swearing has not been premised, he does not make an oath who uses these words: I swear that it is so, because he does not invoke the testimony of God. For although I swear signifies: I invoke God as witness, yet those who use this word alone, unless they have been warned about oath, do not attend to its full sense. God lives, that it is so, is an oath: for the life of God is added in testimony of truth.

b. Formulas of implicit oath are: I swear by the Blessed Virgin, by the cross, by the holy Gospels, by the altar, by the sacraments, by the Catholic faith, by the Church, by the saints, by the temple, by my soul, by heaven, etc.; for he who swears thus is judged to invoke the author or lord of these. In practice, however, those who frequently use these words: bei Gott, bei meiner Seele, etc., do not think of God; therefore from defect of intention these formulas often do not contain oaths.

c. Ambiguous formulas are: by my oath (auf meinen Eid); by my conscience; by my faith; God lives; God is truth; God knows; I speak before God, etc. These and words of this kind are true oaths if the intention of swearing accedes, or if they are required in the judicial forum as oath-words; but if the intention of swearing is not established, they are judged to be uttered only enunciatively, for procuring greater belief, not invocatively for invoking divine testimony. Wherefore if in common conversation the formulas are used: ich schwore dir einen Eid, dass ich das tun werde; bei meinem Eide tue ich das, most intend by these words not seriously to swear, but to affirm more gravely.

d. Oath-formulas are not: truly; certainly; in truth; it is as certain as it is certain that I exist, that I am here, that the sun shines, etc.; nor: may I die, may my ears be cut off, may the devil destroy me, if this is not true: for these and things of this sort contain a certain exaggerated confirmation of truth, not an oath, because invocation of divine testimony is lacking. Wherefore if what is affirmed by these formulas is false, only a venial lie is committed. Nevertheless, if the formula contains a penalty to be inflicted by God: may I be struck by lightning, if it is not true, it can more easily be held to be an oath-formula.

e. If an assertion or promise is exacted from priests and furnished through their consecration: bei meiner priesterlichen Ehre und Treue, there is not question of a true oath, but of a firmer and more secure affirmation of truth, according as it befits a priest to affirm or promise. The same must be said of the formula which princes are accustomed to use: bei meiner fuerstlichen Ehre und Treue.

f. Formulas by which the truth of an assertion is compared with the truths of faith: It is as true as God exists - as Christ is in the venerable sacrament - as the Gospel is true; I am as innocent as the Blessed Virgin, etc., seem to some to contain an oath with blasphemy. Nevertheless they certainly contain neither an oath, because no one is invoked as witness, nor blasphemy, provided that what is affirmed is true, because the one uttering intends to signify only a likeness between the certitude of his assertion and the certitude of revealed truth, not equality. Therefore he who uses formulas of this kind sins venially by vain invocation of the divine name, provided the thing is true; but if the asserted thing is false, he commits blasphemy objectively, because he contemptuously compares his lying speech with divine speech or existence.

248. The conditions of a licit oath from Jer. 4:2 are three: "Thou shalt swear: the Lord liveth, in truth and in justice and in judgment"; for if one of these conditions is lacking, the oath lacks the reverence owed to God.

1. The truth of an oath requires that a lie be excluded from the oath; therefore in an assertory oath it requires that that which is asserted be so, or at least be believed to be so, as it is asserted; but in a promissory oath, that the one swearing have the will of afterward fulfilling what he promises.

a. It is not lawful to swear with only probable knowledge of the matter, but certain knowledge of the thing which is sworn is required; however, that moral certitude suffices which is had when no prudent and reasonable doubt militates against the thing. If one must swear concerning the deed of another, which is known from the report of a man worthy of faith, outside judgment indeed it is lawful to swear, because morally certain knowledge of the thing is had; but in judgment it is not lawful to swear unless the fact is known by one's own experience: for an oath in judgment, unless something else is expressly said, is understood of one's own knowledge.

b. Therefore he who swears with doubt concerning the truth sins gravely, because he wills that God testify to it, whether it is true or false. - And he who in judgment swears to a thing indeed true and certainly known, of which nevertheless he does not have experimental knowledge, commits perjury. - He who makes a promissory oath without the mind of executing the thing promised, likewise he who doubts whether he will do what he swears, and finally he who judges the thing promised to be morally impossible for himself, swears falsely.

c. Whether it is licit to swear with mental restriction. alpha. To swear with purely mental restriction is perjury; beta. to swear with broadly mental restriction before those who have the right of knowing the whole truth is mortal; gamma. to swear without a just cause, with broadly mental restriction before those who do not have this right, is venial; delta. but from a just cause it is licit: for since the assertion is true, God is not invoked in testimony of falsehood. Nevertheless, a greater cause is required for making restriction with an oath than if it is made without an oath.¹

2. Justice in an assertory oath consists in this, that the one swearing can licitly communicate with others the thing which he asserts; but in a promissory oath it consists in this, that the thing promised is licit and honorable.

Thus he swears against justice (by an assertory oath) who without a just cause reveals another's hidden crime with an oath; likewise he who with an oath boasts about a duel committed. He swears against justice (by a promissory oath) who obligates himself by oath to telling a lie, to committing a duel, to inflicting damage upon another.

3. Judgment or discretion in an oath requires two things: first, that a just cause of swearing be present; then, that the oath itself be furnished with that external and internal reverence which befits the divine majesty. But any cause of necessity or of great usefulness is judged just.

¹ Cf. St. Alphonsus, l. 3, n. 151.