Section 1: Definition and Division of Oaths

1. An oath (iuramentum, iusiurandum) is the act of calling on God to witness that a statement is true, or to make the fulfilment of a promise binding under a more solemn obligation*.¹

¹ H. Busembaum, S.J., Medulla Theol. Mor., l. III, tr. 2, dub. 1: “This invocation consists in this: that one who swears, so far as lies in him, desires or wills God to attest and manifest that which he swears (if and when, of course, it shall please Him, whether in this life or in the other), as something known by God Himself and true.”

The invocation of the divine name means that he who takes an oath calls upon God to testify to the truth of his statement or the sincerity of his promise, under penalty of forfeiting the divine help and grace if he swears falsely. For this reason an oath is an act of extraordinary divine worship (actus religionis secundarius.)

In taking an oath we may call on God expressly or tacitly. We do so expressly (iuramentum explicitum) if we mention Him by name; we do so tacitly (iuramentum implicitum) when we swear by some creature which stands in a special relation to God, such as the angels and saints, the cross of Christ, the Gospels or the Sacraments.

2. With regard to its purpose an oath is either assertory or promissory. a) In an assertory oath (iuramentum assertorium) we call upon God to witness that what we say is true and not otherwise. This kind of oath is employed chiefly in law courts. In its more solemn form (adiuratio) it differs from a simple oath in this that the taker does not call upon God as a witness, but merely uses His name in order to ascertain the truth by an appeal to the reverence due to His Divine Majesty and to sacred persons and things.² b) A promissory oath (iuramentum promissorium) is one in which God is called upon as a witness to the fulfilment of a future promise or event. Such an oath is, e. g., that taken at a solemn betrothal or by a soldier on the flag.

² Gury, Comp. Theol. Mor., I, n. 295: “An oath is to be distinguished: 1. as assertory or promissory, according as truth alone is asserted by it, or a promise or agreement is confirmed; 2. as solemn or simple, according as it is made in a form required by law or with solemn ceremonies, or privately with those excluded; 3. as explicit or implicit, according as God is expressly invoked as witness of the truth, or creatures in whom divine attributes especially shine forth are employed in testimony. There is also an imprecatory oath, by which God is invoked at once as witness and avenger of perjury.”—Ibid., n. 305: “Adjuration is an authoritative and entreating demand, made by interposing the name of God or of the saints or of a sacred thing, in order that another may be induced to do or omit something. It differs, therefore, from an oath in this, that it does not introduce God as witness but only interposes His name in order to obtain the desired thing more efficaciously because of the reverence due to the divinity or to sacred things.”

A subspecies of the promissory oath is that called iuramentum comminatorium, when God is called upon as a witness that the person who takes the oath has the present intention of injuring his neighbor and as a guaranty that this purpose will be carried out some time in the future.

3. With regard to form an oath may be (a) verbal, real, or mixed; (b) solemn or simple. a) A verbal oath (iuramentum verbale) is one clothed in words. A real oath (iuramentum reale) takes the form of an action, e. g., raising the right hand. A mixed oath (iuramentum mixtum) is one in which words are combined with actions, as in touching the book of the Gospels while pronouncing the usual formula.

In the Middle Ages persons when swearing often touched the Blessed Sacrament, relics of the Saints, sacred vessels, etc. Such an oath was called corporal (iuramentum corporale), a term which has nothing to do with the corporal or linen cloth on which the Sacred Host is laid, but simply refers to corporal or bodily contact with the sacred object.³

³ Catholic Dictionary, 9th ed., p. 617, London 1917.

b) A simple oath (iuramentum simplex) is one taken without ceremonies. A solemn oath (iuramentum solemne) is one clothed with the ceremonies prescribed by law, such as holding up the right hand or kissing the Bible.

These differences are all formal and do not affect the substance of an oath nor do they pro- duce various degrees of obligation. A simple oath is just as binding as a solemn oath, and one made interiorly is as valid as if it were clothed in words or manifested by actions. But the use of symbols and ceremonies is calculated to emphasize the sacredness of the act and consequently has a salutary effect on the minds of men.

Sometimes an imprecation is added to an oath, as, e. g., “So help me God.” In this case we have an imprecatory oath; others are called invocatory.⁴

⁴ Thos, Slater, S.J., 4 Manual of Moral Theology, I, 240.

READINGS.—St. Thomas, Summa Theol., 2a 2ae, qu. 89–90.—IDEM, Comment. in Sent., III, dist. 39.—St. Bonaventure, Comment. in Sent., III, dist. 39 (Opera Omnia, III, 861 sqq.).—St. Alphonsus, Theol. Mor., l. III, n. 133–193 (ed. Gaudé, I, 460).—F. Suarez, De Religione, tract. V.—F. X. Linsenmann, Lehrbuch der Moraltheologie, pp. 445 sqq.—J. B. Wirthmüller, Die moralische Tugend der Religion, pp. 380 sqq.—F. A. Göpfert, Der Eid, Mayence 1883.—Thos. Slater, S.J., A Manual of Moral Theology, Vol. I, pp. 240 sqq.—Thos. Bouquillon, De Virtute Religionis, Part III, Bruges 1880.—Ballerini-Palmieri, Opus Theol. Mor., Vol. II, 3rd ed., n. 532–601.—H. Noldin, S.J., Summa Theol. Mor., Vol. II, pp. 253 sqq.—A. Lehmkuhl, S.J., Theol. Mor., Vol. I, pp. 308 sqq.