2252. Cooperation in Sinful Oaths.—(a) Formal cooperation is never lawful, because it makes the cooperator will the guilt of what is done. Thus, he who by command, counsel, promise, etc., induces another to swear falsely is guilty as the principal or accessory to the crime (see 1513, 1778).
(b) Material cooperation is lawful when there is a sufficient reason for it, as when a public official demands the oath according to law from a person who, as he knows, will swear falsely. For the public good demands that in certain cases oaths be administered, notwithstanding that for some persons this will prove an occasion of perjury. But the lawgiver should not multiply temptations by demanding sworn statements unnecessarily; otherwise the oath becomes a mere formality deprived of proving value, and the crime of perjury is made common.
2253. Sinful Oaths Demanded or Accepted by Private Persons.—(a) Incautious or Disrespectful Oaths.—It is not lawful to ask or receive an oath, when there is no great public or private need for it; otherwise one makes a sacred act cheap and common. Neither is it lawful to ask or receive an oath from those who do not believe in oaths (e.g., the Mennonites, some Quakers); otherwise one compels another to swear against his conscience and indevoutly. Those who believe that oaths are sinful may be required, nevertheless, to bind themselves on their solemn word of honor, and may be punished in the same manner as perjurers if they speak falsely.
(b) Perjured Oaths.—It is not lawful for a private person to ask or receive an oath from another, if he is sure that the latter will commit perjury; but one may ask and receive an oath, even though one does not know whether the other person will swear truly or not, if one has a sufficient reason.
(c) Wicked Oaths.—It is clearly unlawful to ask or receive a wicked oath, in which something sinful is promised or stated; for the thing itself is then desired and there is formal cooperation. But it is not necessarily sinful to ask or receive a wicked oath, in which the sinfulness is found, not in the matter of the oath, but in the dispositions of the swearer, for there may be only material cooperation. Thus, he who exacts a sworn promise of murder agrees to murder, but he who demands a sworn statement against a third party for which there is necessity does not necessarily agree to hatred, if the person taking the oath swears out of hate or revenge.
2254. Fictitious Oaths.—A fictitious oath is one in which a person swearing externally has no intention internally to call on God as a witness.
(a) This kind of oath is invalid, for, as was just said, without a real intention to swear there is no oath. Hence, a fictitious oath produces no obligation of religion, but there may be an obligation of justice, as when the oath is the unjust cause of damage to another.
(b) This kind of oath is sinful, for, if it testifies to error, it includes the grave sin of external dishonor to God; if it testifies to truth, it includes the venial sin of taking God’s name in vain. The fictitious oath is a grave sin if the circumstances are such that a sincere oath is gravely obligatory, as when a superior or judge lawfully imposes an oath in a serious matter, or the parties to an important onerous contract bind themselves by oath in order to strengthen their pact.
2255. Expressions Confused with Oaths.—Expressions that are sometimes mistakenly confused with sinful swearing are the following: (a) profane or vulgar talk, such as “Hell,” “The devil,” “Doggone it”; (b) cursing, such as “Go to hell,” “God damn you,” “Damn it”, (e) contumely, such as “bastard,” “son of a bitch”; (d) vain use of the name of God, such as “by God,” “Christ,” etc., when used as common exclamations; (e) temptation of God, such as: “If there is a God, may He strike me dead!”; (f) blasphemy, such as: “May God perish, if this is not true!”
The expressions, “This is as true as the Gospel,” “God’s own word is not more truthful,” “I am as innocent as the Blessed Virgin,” etc., if used to confirm the truth, are not meant to assert the speaker’s equality to God and the Saints, and hence they are venial sins of taking the Lord’s name in vain. But, if they are used to confirm error, they are mortal sins of blasphemy.