Ethically the subject of self-defense regards the right of a private person to employ force against any one who unjustly attacks his life or person, his property or good name. While differing among themselves on some of the more subtle and less practical points comprised in this topic, our moralists may be said to be unanimous on the main principles and their application regarding the right of self-defense. The teaching may be summarized as follows:
Everyone has the right to defend his life against the attacks of an unjust aggressor. For this end he may employ whatever force is necessary and even take the life of an unjust assailant. As bodily integrity is included in the good of life, it may be defended in the same way as life itself. It must be observed however that no more injury may be inflicted on the assailant than is necessary to defeat his purpose. If, for example, he can be driven off by a call for help or by inflicting a slight wound on him, he may not lawfully be slain. Again the unjust attack must be actually begun, at least morally speaking, not merely planned or intended for some future time or occasion. generally speaking one is not bound to preserve one's own life at the expense of the assailant's; one may, out of charity, forego one's right in the matter. Sometimes, however, one may be bound to defend one's own life to the utmost on account of one's duty of state or other obligations. The life of another person may be defended on the same conditions by us as our own. For since each person has the right to defend his life unjustly attacked, what he can lawfully do through his own efforts he may also do through the agency of others. Sometimes, too, charity, natural affection, or official duty imposed the obligation of defending others. A father ought, for example, to defend the lives of his children; a husband, his wife; and all ought to defend the life of one whose death would be a serious loss to the community. Soldiers, policemen, and private guards hired for that purpose are bound in justice to safeguard the lives of those entrusted to them.
It is lawful to defend one's material goods even at the expense of the agressor's life; for neither justice nor charity require that one should sacrifice possessions, even though they be of less value than human life in order to preserve the life of a man who wantonly exposes it in order to do an injustice. Here, however, we must recall the principle that in extreme necessity every man has a right to appropriate whatever is necessary to preserve his life. The starving man who snatches a meal is not an unjust agressor; consequently it is not lawful to use force against him. Again, the property which may be defended at the expense of the agressor's life must be of considerable value; for charity forbids that in order to protect ourselves from a trivial loss we should deprive a neighbor of his life. Thefts or robberies, however, of small values are to be considered not in their individual, but in their cumulative, aspect. A thief may be slain in the act of carrying away stolen property provided that it cannot be recovered from him by any other means; if, for example, he can be made to abandon his spoil through fright, then it would not be lawful to shoot him. If he has carried the goods away to safety he cannot then be killed in order to recover them; but the owner may endeavor to take them from him, and if the thief resists with violence he may be killed in self-defense.
Since it is lawful to take life in the legitimate defense of one's material goods, it is evidently also lawful to do so in defense of chastity which is a good of a much higher order. With regard to honor or reputation, it is not lawful to kill one to prevent an insult or an attack upon our reputation which we believe he intends, or threatens. Nor may we take a life to avenge an insult already offered. The proceeding would not be defense of our honor or reputation, but revenge. Besides, in the general estimation honor and reputation may be sufficiently protected without taking the life of the offender.
Zigliara, Summa Philosophica, III, I, iii; St. Thomas, Summa Theolgica, II-II, Q lxvii, a. 7; Billuart, Cursus Theolgiae: in II-II St. Thomae, d. X, a. V.
APA citation. (1912). Self-Defense. In The Catholic Encyclopedia. New York: Robert Appleton Company. http://www.newadvent.org/cathen/13691a.htm
MLA citation. "Self-Defense." The Catholic Encyclopedia. Vol. 13. New York: Robert Appleton Company, 1912. <http://www.newadvent.org/cathen/13691a.htm>.
Transcription. This article was transcribed for New Advent by Chuck Cilek.
Ecclesiastical approbation. Nihil Obstat. February 1, 1912. Remy Lafort, D.D., Censor. Imprimatur. +John Cardinal Farley, Archbishop of New York.