Front Page Titles (by Subject) QUESTION LXXXIX.: OF OATHS. - Aquinas Ethicus: or, the Moral Teaching of St. Thomas, vol. 2 (Summa Theologica - Secunda Secundae Pt.2)
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QUESTION LXXXIX.: OF OATHS. - St. Thomas Aquinas, Aquinas Ethicus: or, the Moral Teaching of St. Thomas, vol. 2 (Summa Theologica - Secunda Secundae Pt.2) 
Aquinas Ethicus: or, the Moral Teaching of St. Thomas. A Translation of the Principal Portions of the Second part of the Summa Theologica, with Notes by Joseph Rickaby, S.J. (London: Burns and Oates, 1892).
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Article I.—Is swearing a calling on God to witness?
R. As the Apostle says: “An oath is for confirmation.”1 In matters of science, confirmation is done by reasoning from premises of natural knowledge, that are infallibly true. But the particular facts of the contingent doings of men cannot be confirmed by necessary reasoning; and therefore what is alleged concerning them is usually confirmed by witnesses. Still human testimony is not sufficient for such confirmation, and that on two accounts. First, for lack of truthfulness in man, seeing that very many fall into lying. Secondly, for lack of knowledge, because men cannot discern things to come, nor the secrets of hearts, nor yet the doings of the absent. Still however men talk on all these points; and it is expedient for human society that some certainty should be had about them. And therefore it has been found necessary to recur to the witness of God; because God cannot lie, nor is anything hidden from Him.
Now to call God to witness is to swear,—sometimes about things present or past, which is an oath of asseveration; sometimes in confirmation of a future performance, and that is called a promissory oath.
Article II.—Is it lawful to swear?
R. A thing may very easily be good in itself, and yet turn to his evil who does not use it properly. Thus to receive the Eucharist is good, and yet he who receives unworthily “eateth and drinketh judgment to himself.”1 Thus then an oath is a lawful and virtuous thing in itself, as is evident from its origin and its end. From its origin: because the taking of an oath was brought in by the belief of mankind that God has infallible truth, possesses a universal knowledge, and exercises a universal providence over all things. From its end, because oaths are taken to justify men and put an end to disputes. But an oath works to the evil of a man through his using it badly, without necessity and due caution. Small indeed seems to be his reverence for God, who brings God in as witness to a light matter, which he would not presume to do with any man of honourable position. There is also the danger of perjury, because a man easily errs in word. Hence it is said: “Let not thy mouth be accustomed to swearing; for in it there are many falls.”2
Article III.—Are these three duly enumerated accompaniments of an oath,—justice, judgment, and truth?3
R. There are two requisites for the good use of an oath: First, that one should not swear lightly, but with a necessary cause, and discreetly: in this respect judgment is necessary, or discretion on the part of him who swears. Secondly, touching the matter sworn to, it is requisite that it be neither a falsehood nor anything unlawful; and in this respect truth is necessary, whereby one swears to what is true; and justice, whereby one swears to what is lawful. Judgment is wanting in an incautious oath; truth in a lying oath; and justice in an iniquitous or unlawful oath.
Article V.—Is swearing something desirable and frequently to be practised, as a thing useful and good?
R. That which is sought only as a support and stay to infirmity and deficiency, is not counted of the number of things in themselves desirable, but of the number of things necessary, as in the case of medicine. But an oath is sought as a support and stay to the deficiency of the faith that one man can put in another. And therefore an oath is not to be held of the number of things that are in themselves desirable, but of the number of things that are necessary for this life, and which are unduly used by whosoever uses them beyond the bounds of necessity.
§ 1. The case of a simple affirmation is different from that of an oath, in which the witness of God is invoked. For the truth of a simple affirmation it is enough that the person says what he intends to do, because that is true at the time in his case, or in the purpose of the doer. But an oath ought not to come in except upon a matter on which the person’s mind is immovably made up. And therefore if an oath is used, then for reverence of the witness of God that is invoked, the man is bound to make true what he has sworn to, to the best of his power, unless the issue is for the worse.
§ 2. An oath may issue for the worse in two ways. In one way from the beginning, either because the oath is of itself evil, as when one swears to commit adultery; or because it is an obstacle to greater good, as when one swears not to enter the religious or the ecclesiastical state,1 or not to accept a prelacy in a case where it is expedient to accept it. An oath of this kind is unlawful from the beginning. That however it may be in different ways. In the case of a person swearing to commit a sin, he sinned in swearing, and he sins in keeping the oath. But if a person swears not to do that which is the better good, good however which he is not bound to do, he sins, to be sure, in swearing, inasmuch as he places an obstacle to the Holy Ghost, the inspirer of good purposes, but he does not sin in keeping the oath, though he does much better not to keep it. In another way an oath has issue for the worse on account of something fresh that comes up unforeseen. Thus Herod’s oath to give the dancing girl whatever she asked, might have been lawful from the beginning, the due condition being understood, that she should ask what was a proper thing to give, but the fulfilment of the oath was unlawful.
§ 3. In an oath taken on compulsion there is a twofold obligation: one to the man to whom the promise is made; and such obligation is destroyed by the compulsion, because he who has used violence deserves that the promise made to him be not kept.1 There is another obligation binding the person to God, to fulfil what he has promised by His name. Such obligation is not destroyed in the court of conscience; he who has sworn should rather suffer temporal loss than violate his oath. Still he may take legal measures to recover what he has paid, or he may denounce the matter to his ecclesiastical superior, any oath to the contrary notwithstanding: because such an oath would have issue for the worse, being against public justice. The Roman Pontiffs have absolved men from oaths like these, not as ruling such oaths to be of no binding force, but relaxing the force of them for just reasons.
§ 4. When the intention of the party taking the oath is not the same as the intention of the party to whom it is taken—if this comes of any guile in him that swears, the oath should be kept according to the sound understanding of him to whom it is taken.1 But if the person taking it uses no guile, he is bound according to his intention in taking it.
Article VIII.—Is the obligation of an oath greater than that of a vow?
R. Both obligations, that of an oath and that of a vow, are caused by something referring to God, but not in the same way. The obligation of a vow is caused by the fidelity which we owe to God, to discharge our promise to Him; while the obligation of an oath is caused by the reverence that we owe Him, which binds us to make true whatever we promise by His name. Now every violation of fidelity involves irreverence, but it is not every irreverence that contains a violation of fidelity. A subject’s violation of the fidelity that he owes his lord, is reckoned the greatest irreverence. And therefore a vow in its own nature is more binding than an oath.
Article IX.—Has any one the power to dispense from oaths?
R. The need of a dispensation, whether from a law or from a vow, arises from the fact that what is useful and right in itself, viewed generally, may be wrong and hurtful in a particular set of circumstances: and what is wrong and hurtful cannot be matter either of law or vow. The same is out of keeping with the conditions requisite to an oath: for if it is wrong, it is out of keeping with justice; if it is hurtful, it is out of keeping with judgment. And therefore parity of reason proves that a dispensation may be granted also from an oath.
§ 1. A dispensation from an oath does extend to the man’s doing anything against his oath: that is impossible, since the observance of oaths is matter of divine precept, which admits of no dispensation.1 But the effect of a dispensation from an oath is, that what formerly fell under oath, falls under oath no longer, not being due matter of oath, as we said above of a vow.2 The matter of an oath of asseveration, which is of the present or past, is already gone into the region of necessity and become immutable; and therefore a dispensation could not refer to the matter, but would refer to the act itself of swearing; hence such a dispensation would be directly against the divine precept. But the matter of a promissory oath is something future, capable of variation, so that in a certain conjuncture it may be unlawful or hurtful, and consequently not due matter of oath; and therefore a dispensation may be granted from a promissory oath, because such a dispensation regards the matter of the oath, and is not contrary to the divine precept of the observance of oaths.3
§ 2. There are two ways in which a man may promise something under oath to another. One way is when he promises something to that other person’s benefit, as that he will serve him, or give him money. He to whom the promise was made, can absolve from such a promise; for the maker of the promise is understood to have discharged his promise to the other, when he acts in the matter according to that other’s will. The other way is when one promises to another something that makes for the honour of God, or for the advantage of a third party; as when one promises another under oath to enter religion, or to do some work of piety; and then he to whom the promise is made cannot absolve the promiser; because the promise was made not to him mainly, but to God; unless it happens that a condition has been inserted, giving him that power.
§ 3. Occasionally a thing is promised on oath, of which it is doubtful whether it is lawful or unlawful, beneficial or hurtful, either absolutely or in a special case; and from such an oath any Bishop can dispense.1 Sometimes again a thing is promised on oath, which is manifestly lawful and useful; and in such an oath there seems to be no room for dispensation or commutation, unless something better occurs to be done for the common advantage, which seems to appertain above all to the power of the Pope, who has care of the Universal Church. Or even there may be an absolute relaxation of the oath, which again appertains to the Pope in all things alike that are part of the administration of Church matters, over which he has plenitude of power. In the same way any man in authority may make void an oath that has been taken by his subjects in the matter that is subject to his authority. Thus a father may make void the oath of one but yet a girl in age, and a husband his wife’s oath, as is said in Numbers xxx.
[1 ]Hebrews vi. 16.
[1 ]1 Cor. xi. 29.
[2 ]Ecclus. xxiii. 9.
[3 ]Jerem. iv. 2.
[1 ]Absolutely, such an oath is an obstacle to greater good. In a particular case it is not, especially when taken to a public authority, who can release you where he sees cause. (Trl.)
[1 ]This supposes the violence to be unjust. The promise in such a case is a promise, but the maker of it has it in his discretion to rescind it: in technical language, it is valid but not firm. How far one may be justified in making such a promise, is a further question. It will be seen that when the promise has been confirmed by oath, it cannot be rescinded except by Church authority. See also II-II. q. 98. art. 3. § 1. This should prevent a nation from tearing up treaties, on the plea that the war which imposed them was unjust, at leas: when the present rulers of the nation have sworn to those treaties. Cf. II-II. q. 98. art. 2. § 4. But international law is a terrible tangle, for want of an international judge. (Trl.)
[1 ]E.g., Cranmer’s oath at his consecration, Ethics and Natural Law, p. 234. (Trl.)
[1 ]I-II. q. 100. art. 8. (Trl.)
[2 ]Q. 88. art. 10. § 2.
[3 ]This paragraph should be studied by those historians who have put it on record, that the Pope has at times granted dispensations to commit perjury. (Trl.)
[1 ]In his own diocese. (Trl.)