Chapter II — Several heretics who condemn the sacred oath as unlawful. Their errors are reviewed. The oath is shown to be an honorable act, lawful for Christians, and the fruit of the virtue of religion, or of latria

I. Alphonso a Castro reviews several heretics, both ancient and recent, who condemned all oaths (Bk. VIII, s.v. Iuramentum). The ancient heretics who taught that any oath whatsoever is unlawful for Christians are the Albanenses, the Bagnolenses, or Baiolenses, the Cathari, and the Pelagians. The more recent are the Waldensians, the Pseudo-Apostles, and the Wycliffites. For among the forty-five propositions of John Wycliffe condemned in the Council of Constance (session 45, year 1418), this one is found, which stands in the order 43rd: "Oaths are unlawful, which are made to corroborate human contracts and civil commerce."

II. To establish this error of theirs, the aforesaid heretics produce several arguments, drawn both from Scripture and from reason. From Scripture, indeed, they cite Hosea 4: "Neither shall they swear: 'The Lord liveth'"; and that of Zechariah 5: "Every thief shall be judged... and every one that sweareth in like manner shall be judged." They also press several passages from the Gospel. First, they object that of Matthew 5: "You have heard that it was said to them of old: Thou shalt not forswear thyself, but thou shalt perform thy oaths to the Lord. But I say to you not to swear at all, neither by heaven, for it is the throne of God; nor by the earth, for it is his footstool; nor by Jerusalem, for it is the city of the great king; neither shalt thou swear by thy head, because thou canst not make one hair white or black. But let your speech be: yea, yea; no, no: and that which is over and above these, is of evil." In this text two things are prescribed. First, an oath is absolutely forbidden — for that particle "at all" seems to signify this. Then a formula for confirming our assertions is designated, in those words: "But let your speech be: yea, yea; no, no; and that which is over and above these, is of evil." James the Apostle likewise, in chapter 5, with such great emphasis, proscribes the oath, that these words which follow inhibit oaths still more forcefully: "That which is over and above these, is of evil": "But above all things, my brethren, swear not, neither by heaven, nor by the earth, nor by any other oath. But let your speech be: yea, yea; no, no: that you fall not under judgment." Three Fathers, too, not obscurely indicate that oaths were forbidden even to Christians. Tertullian, in his book On Idolatry, ch. 20, writes this: "I say nothing of perjury, since it is not even lawful to swear at all." Clement of Rome, or the author of the Apostolic Constitutions (Bk. VI, ch. 11): "Our Master commanded that we should not swear even by the true God, so that our word might be held firmer and more credible than an oath." Finally, this can be confirmed by reason. Since man, being of the lowest rank, cannot bring God forward as witness, especially to confirm human contracts, pacts, and business affairs. For the person of God is of the supreme order: therefore he cannot be invoked to confirm these inferior transactions, without a monstrous perversity of order.

III. It is a truth of faith that not every oath is forbidden, or unlawful, for Christians. St. Thomas (II-II, q. 89, art. 2) establishes this assertion both by the authority of Scripture, by reason, and by the examples of the Saints. That an oath is, by its own nature, honorable, he demonstrates from its origin and its end. From its origin, indeed, because an oath is introduced from the faith by which men believe God to have infallible truth, and universal knowledge and providence of all things. From its end, however, because an oath is brought in to justify men, and to end controversies. Then he shows that God himself commanded an oath — which he would never have done, if an oath were, by its own nature, unlawful. Now Deuteronomy 6 has this: "Thou shalt fear the Lord thy God, and shalt serve him only, and thou shalt swear by his name."

IV. Our assertion is confirmed by the examples of the Saints. The Apostle Paul called God to witness (Romans 1) in these words: "For God is my witness." He also employed an oath (2 Corinthians 1): "But I call God to witness upon my soul, that to spare you, I came not any more to Corinth." What he wrote to the Galatians, he confirmed by oath (ch. 1): "Now the things which I write to you, behold, before God, I lie not." What more? God himself confirmed by oath the promise made to Abraham: "By my own self have I sworn, saith the Lord, because thou hast done this thing," etc. Finally, Christ, the necessary conditions being observed, always approved oaths, and frequently exacted them, whether to abjure heresy, or to purge oneself of crimes, or to end lawsuits, or to confirm obedience — as Paul attests (Hebrews 6), that an oath is the end of all controversy. To the testimonies of Sacred Scripture is added the custom of the Church, which approves the use of oaths, and confirms them, as is held in the titles on heretics, and on the law of oaths, which are more fully declared in the Councils of Ephesus, of Constantinople, and in the title on canonical purgation.

V. To the arguments of the heretics, setting aside the various responses of Jerome, Bernard, and other Fathers, we set forth those which Augustine and Thomas present — for their responses are approved by almost all. Augustine, then (On the Lord's Sermon on the Mount, Bk. I, ch. 17), expounds the described text of Matthew, and interprets it in these words: "It is thus, then, understood that the Lord commanded that one should not swear, not because swearing is good, but lest anyone, through the assiduity of swearing, slide by custom into perjury. Wherefore he who understands that an oath is to be used not as a good, but as a necessity, should restrain himself as much as he can, so as not to use it except from necessity... To this, then, pertains what is said: 'But let your speech be: yea, yea; no, no.' This is good, and to be sought. But that which is more than this, is of evil — that is, if he is compelled to swear, let him know that this comes from the necessity of the weakness of those to whom he persuades something, which weakness is certainly an evil; from which we daily pray to be delivered, when we say: 'Deliver us from evil.' He did not say, then, 'that which is more is evil'... but 'of the evil,' that is, of that man's weakness, on whose account you are compelled to swear." Augustine gives this same response elsewhere (Bk. IV, Against Lying, ch. 15), where he confirms it by the example of Paul: "The Apostle himself swore in his Epistles, and shows that it is a more cautious course not to be found swearing, except in writing, where one considers with care what is said — lest, from the ease of it, one falls into a habit, and thence, from habit, into perjury. And therefore it is not found that he swore verbally, where a precipitate tongue might be considered." St. Thomas, in the place cited, adopts these two responses of Augustine, and by them resolves the first and second arguments. And by these, too, the response to James's authority is made clear, who speaks in the same sense as Matthew.

VI. To the testimonies of the Fathers we say that they disapproved the easy use of swearing, but by no means denied that it was necessary. It is indeed true that they did not assign this exception, since it was by no means necessary for them to do so — just as Christ did not declare this exception either, as Sotus notes (On Justice and Law, Bk. VIII, art. 2). For since they were then reprehending men inclined, through habit, toward swearing, it did not at all pertain to their purpose to teach them that it was sometimes lawful to swear — since this was already manifest through the very persons to whom they spoke. This same thing happens to us commonly: when we reprove some vice, we do not always explain the opposite virtue. Augustine's teaching confirms this interpretation, which he presents not as merely probable, or recently discovered, but as common, and subject to no controversy. As to the argument from reason, it is said that man cannot induce God, by his own voice or sign, to show the truth; nor does this truth depend on the one to whom the oath is sworn; but man only calls God to witness, so that what he asserts may merit greater authority and credit among other men, and become more credible — which suffices for the utility of the oath. This is well shown by the deed of St. Basilides the Martyr, of whom Ambrose writes this: "When Basilides was pressed by his fellow-soldiers to swear by the fates" — since he was a Christian... , he judged it wrong for himself to do this, and openly professed it." Eusebius likewise objects (Bk. VI, Ecclesiastical History, ch. 5), affirming that it is unlawful for all... But the common response is that this soldier, recently made a Christian, was ignorant of the rules which Christians observed in the use of oaths. And since he observed that Christians abstained from oaths with the utmost caution, because they swore only under urgent necessity, he falsely judged that an oath was not permitted to Christians at all. Besides which, he was induced to swear not by a judge, but by his fellow-soldiers, and perhaps by their false deities: for this reason he refused to swear.

VII. An oath, then, is lawful for Christians, the conditions being observed which we shall explain below. Indeed, St. Thomas, after having demonstrated in article 1, against the heretics, that an oath is lawful and honorable, shows in article 4 that it is an act of the virtue of religion, or of latria — since one who swears, invoking God as witness, confesses the faithfulness of God, in that he acknowledges God as the first truth, and the founder and provider of all things. Just as, then, prayer, whereby God is invoked as helper, is an act of religion, so too an oath, whereby he is invoked as witness of the truth, is an act of religion: in both cases, the Angelic Doctor concludes, it is manifest that reverence is shown to God. Whence it is clear that an oath is an act of religion, or of latria.