Oaths are appeals to God in witness of the truth of statements or of the binding character of promises. The oath has been in use among all peoples; it continues to be regarded as a useful social institution and a formal guarantee of truthfulness necessary in organized society. Some (e.g., the Quakers) have interpreted Mt 5.4 to be an absolute prohibition of oaths, but Christ's words are a condemnation only of the type of trivial or profane oaths that were permitted under pharisaical casuistry (see oaths in the bible).
There was some difference of opinion among the Fathers of the Church regarding the licitness of oaths. Chrysostom regarded them as a snare of the devil to be avoided under all circumstances (Serm. ad pop. Ant. 15; In Act. Apost. hom. 8). Augustine was not concerned about a gospel prohibition, but thought that the oath should be avoided because of the danger of perjury that would arise from the frequent use of it (In psalm. 88.4; De mend. 28). Others, basing their arguments on New Testament usage, especially on the example of St. Paul, who frequently expressed himself in language indistinguishable from an oath (e.g., 1 Thes 2.5; 2 Cor 1.23; Gal 1–20; Rom 1.9), thought the taking of oaths was permissible in proper circumstances. This view prevailed in Christian times. Oaths became part of the judicial procedure; and oaths pledging fealty, fidelity, or the faithful performance of the duties of an office were recognized as having a social value. Theologians have generally held that an oath taken under proper conditions is not only licit but is also an act of the virtue of religion inasmuch as it is an expression of homage to the wisdom and power of God (St. Thomas Aquinas, Summa Theologiae, 2a2ae, 81.2).
By reason of the matter with which it is concerned an oath is either assertory (declaratory), that is, it calls upon God to witness that one is speaking the truth; or it is promissory, that is, it calls upon God to guarantee one's pledge to do or not to do something. In mode, an oath is either invocatory or imprecatory. In the former, one calls upon God as a witness; in the latter, one invites God's punishment if what is sworn to is false. An oath may also
be either implicit or explicit. In the one, God is mentioned by name; in the other, the formula or gesture used is generally understood to imply the invocation of Him.
To be licit, an oath demands truthfulness, judgment (prudence), and justice (Jer 4.2). The first of these conditions requires the person who takes the oath to speak truly and, in the case of a promissory oath, to be sincere in his intention to fulfill his promise. Judgment, or prudence, requires sufficient reason for taking the oath. In an assertory oath justice demands that the statement should not be sinful (as would be the case, for example, if it were defamatory); in a promissory oath, that which is promised should be morally lawful.
In the case of the promissory oath, the object of the promise must be possible and morally good. A promise of what is impossible, evil, or vain dishonors God and has no binding force. Moreover, it is understood that one undertakes to keep the promise only so long as the fulfillment remains morally possible, provided legitimate authority does not forbid it, and provided no notable change occurs in the matter of the promise, and the beneficiary of the promise does not yield his right to the fulfillment.
Because God is called to witness in an oath, the Church, as the official representative of Christ, legislates on the taking of oaths and claims the power of releasing those who are bound by promissory oaths.
See Also: perjury.
Bibliography: t. aquinas, Summa Theologiae, 2a2ae, 89. h. davis, Moral and Pastoral Theology, rev. and enl. ed. by l. w. geddes (New York 1958) 2:44–48. h. noldin, Summa theologiae moralis, rev. a. schmitt and g. heinzel, 3 v. (Innsbruck 1961–62); v. 1 contains complementa, De castitate and De poenis ecclesiasticis, separately paged, 2:208–223. n. iung, Dictionnaire de théologie catholique, ed. a. vacant et al., 15 v. (Paris 1903–50; Tables générales 1951–) 14.2:1940–56.
"Oaths." New Catholic Encyclopedia. . Encyclopedia.com. (August 15, 2018). http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/oaths
"Oaths." New Catholic Encyclopedia. . Retrieved August 15, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/oaths