(b) Formal ingratitude is a special sin, for it is the denial of a special debt owed in decency, and which a special virtue requires one to pay (see 2374). St. Paul lists ingratitude with other special classes of sin (II Tim., iii. 2).
2379. The Theological Species of Ingratitude.—(a) Formal ingratitude from its nature seems to be a mortal sin, since it is against charity, which bids us love our benefactors. It may be venial, however, on account of the imperfection of the act or the smallness of the matter. Thus, to offend a benefactor in some trifling matter would not be mortal, even though there be some slight contempt in the act.
(b) Material ingratitude is venial or mortal according to the nature of the injury done the benefactor. Thus, a small injury is done when one gives a cheap present to a benefactor from whom one had received a valuable gift, for his right to more was not strict, and hence the sin is venial; but a grave injury is done when one seriously calumniates a benefactor, and the sin is then mortal.
2380. Is It Right to Confer Favors on the Ungrateful?—(a) If the favors will be of benefit, one should not desist merely because of the ingratitude with which they are received. It is not always certain that the beneficiary is ungrateful, and there may be reason to hope for his improvement (Luke, vi. 35).
(b) If the favors are not beneficial, because the recipient is made worse (e.g., arrogant, lazy) through them, they should be discontinued.
2381. The Virtue of Vengeance.—Just as gratitude returns good for evil, so does vengeance (_vindicatio_) return evil for evil, that is, the evil of punishment for the evil of sin. Vengeance is defined as “a moral virtue that inclines a private person to use lawful means for the punishment of wrongdoing, with a view to the satisfaction of public or private justice.”
(a) Vengeance is a virtue of private persons; that is, it belongs to those who are not charged officially with the punishment of offenses. The duty of public persons, such as judges, is a much stricter one and pertains to the virtue of vindictive justice, which is a form of commutative justice; whereas vengeance is only a virtue annexed to justice (see above, 2141 sqq.). Vindictive justice attends to the equality between fault and punishment, vengeance to the protection of the person who has been injured.
(b) Vengeance is concerned with the punishment of wrongdoing, or the infliction of some painful retribution upon one who has already committed an injury. Thus, this virtue is not strictly identical with lawful self-defense, which is directed against an evil that is not past but present, though self-defense may be rated as a secondary act of the virtue of vengeance.
(c) Vengeance uses only lawful means; that is, it seeks redress or reparation from the authorities who have the right to give it and follows due process of law. This virtue differs, then, from private revenge, vendetta, lynch law, exercise of the “unwritten law,” etc., which are acts of sinful violence, though sometimes subjectively excusable on account of ignorance. The virtue of vengeance is also exercised by those who desire that justice may be done against malefactors, or who visit upon them with moderation such punishments as are not forbidden to private persons (e.g., denial of friendship). Parents also exercise this virtue whenever they properly correct and chastise their children.
(d) Vengeance has for its ends public and private justice, that is, the vindication of the right order of society or the compensation or satisfaction of an injured person. If some other good motive causes one to desire requital of evil deeds, the act will pertain to another virtue: thus, if one aims at the amendment of the evil-doer, one’s act pertains to charity; if one desires by the deterrent of punishment to secure the peace and prosperity of the commonwealth, the act is one of legal justice; if one seeks the honor of God, the act is one of religion, etc. If an evil motive prompts the desire of punishment, the wish is not virtuous at all, but sinful. Thus, he who labors to have a criminal captured, sentenced and executed, and whose intention is not the vindication of justice but the gratification of jealousy, hatred, cruelty or other like passion, sins grievously and perhaps makes himself worse than the criminal. To return evil for evil in this way is to be overcome by evil (Rom., xii. 17-21).