Chapter II — On the justice necessary for a promissory oath

I. This condition, which is one of the three necessary for any oath whatsoever, has its chief place in a promissory oath. This justice prescribes that a lawful and honorable matter be promised under oath. Wherefore a promise of unlawful and wicked matter under oath is, by its own kind, a mortal sin. Doctors commonly hand down that the gravity of the matter which falls under the oath must be inspected, so that from this the gravity of the sin against the oath may be gathered. Certain questions will explain the whole matter.

II. Question I. Does one who swears that he will fornicate, or perpetrate any other grave crime, sin mortally against the virtue of religion? Response: All respond affirmatively, since he really has the intention of fornicating; there will be perjury, if the intention of fulfilling what he swears is lacking. Such a swearer, then, commits a twofold sin: one against truth, if the intention of fulfilling what he swears is lacking; the other against the justice of the oath, whether he has or lacks the intention of fornicating — a single, most grave sin, since to bring God forward for the confirmation of iniquity is to inflict a most grave injury on God.

III. Question II. Does one who swears that he will commit some venial sin sin mortally? Response: The common opinion is negative — since it is not a grave injury for the swearer to be bound to the commission of a venial sin. And this is established by the authority of St. Thomas himself: for it does not seem a great matter that one should compel oneself, under the confirmation of one's own resolve, to commit a venial sin, merely by the culpable fault of omitting the execution of the aforesaid oath. Thus more recent authors commonly distinguish.

IV. As for the opinion just reported, if I inspect the multitude of authors whom they cite, the Fathers of Salamanca follow it (tract. 17, ch. 2, punct. 5, n. 54), asserting it more probable; but if I weigh the reasons, I cannot but judge it improbable to me. For indeed, one who swears that he will commit a venial sin invokes God to strengthen and confirm his own resolve. Since, then, some deliberation, or resolve, is fortified by the authority of divine testimony, so that it may become firmer, and more immovable — what is more injurious to God, what more hostile, what more infamous, than to abuse the majesty of his infinite name, and to turn his authority into a support for iniquity? This is confirmed. One who swears without the intention of swearing sins gravely. Why? Because he abuses the oath. But it is a worse abuse when someone uses an oath to confirm venial iniquity. Therefore, etc. It should be added that one who invokes God as witness of a venial sin brings him forward as its surety, and approver; for a witness is summoned to testify, so that he may approve what he confirms by his testimony. What, indeed, is more wicked than to induce God to approve an iniquity, however small? Finally, it is a venial sin to take the name of God in vain — namely, if, without necessity, you swear that you will do something lawful and honorable; but if you swear that you will sin, will you sin only venially? If you swear with the intention of committing that sin, you sin mortally, since you convert the most holy name of God to the confirmation of iniquity, and profane it, and commit an enormous injury against his veracity, whose consent, he to whom every malice, however slight, is utterly repugnant, is asked.

V. Fr. Castropalao confesses that all these considerations seem difficult to him (tract. 14, disp. 1, punct. 6, n. 10); he does not dare, however, to depart from the common opinion; and therefore he offers certain contrived responses. He answers, then, that the swearer does not intend to induce God to approve the iniquity, since the end of the oath is the confirmation of truth. He who converts it, on his part, into a bond of committing iniquity, will he sin only venially? These things, surely, seem too harsh, not to say absurd. An oath, by its own nature, is a sacred thing, whose end is the confirmation of truth. One who, out of a certain vulgar ignorance, swears believing that whatever is promised under oath will be immutable — I too grant that the swearer has no such explicit intention of inducing God to approve iniquity; for, if he explicitly intended this, he would blaspheme. But we say that he does this in effect, by this very fact that he uses divine testimony. The second response, however, is not better than the first — namely, that the swearer is not bound, except under venial obligation, to avoid the preceding sin, because it would be better to avoid a venial than a mortal sin. This is true; but he ought to abstain from the invocation of divine testimony in confirmation of iniquity, even the smallest, since any malice whatsoever, however small, is supremely repugnant to God. Therefore a most grave injury is done to God, as often as he is invoked to confirm the resolve of perpetrating any iniquity whatsoever.

VI. Question III. Does one who swears he will do something against the evangelical counsels — for instance, that he will not accept a prelacy, that he will not enter religious life, and other things of this kind — sin mortally? Response: The most common opinion is that only a venial sin is committed by such a swearer. St. Thomas teaches this (II-II, q. 89, art. 7, ad 2): "If, however, someone swears that he will not do some better good, which nonetheless he is not bound to do, he indeed sins by swearing, insofar as he places an obstacle to the Holy Spirit, who is the inspirer of a good resolve; he does not, however, sin by keeping the oath; but he will do much better, if he does not keep it." Of what kind this sin is, the Angelic Doctor does not absolutely determine; he only resolves that a sin is committed, if such an oath is observed.

From this it is gathered — since it is a sin to swear the omission of a greater good — how much graver a sin it is to swear the commission of a positive iniquity, though light. Of the former kind of oaths, if you observe them, you do not sin, because you were not absolutely bound to enter religious life; but you do sin by observing the latter kind. If, however, someone omitted the execution of some evangelical counsel, for this reason chiefly, that he had sworn such an omission, he would, without doubt, sin mortally — since there would be at least a tacit error in faith, if he believed that an oath obliges to the omission of those things which conduce to the attainment of evangelical perfection.