1824. Is Tyrannicide Lawful?—(a) If the ruler is a tyrant in act (that is, one who has a lawful title to rule but who abuses his authority), it is not lawful to kill him on account of his misdeeds or crimes, since the subject has not the authority to act in the name of the nation (Rom., xiii. 1 sqq.; I Peter, ii. 18). In case of self-defense, however, as when the tyrant unjustly makes a personal attempt on the life of a citizen, the latter has the right to kill. The Council of Constance condemned the doctrine of Wycliff that every subject has the right to assassinate a tyrannical prince, a doctrine that would make the position of every ruler unsafe, since there are always persons who think they are victims of persecution. The nation, however, has the right to depose or even to execute a wicked ruler, for government is given to rulers for the benefit, not for the destruction, of the common good.
(b) If the ruler is a tyrant in title (that is, a usurper), it is not lawful to kill him, when he has already obtained peaceful possession; for here again it cannot be said that the killer would have the authorization of the nation. If, however, the tyrant has not obtained possession but is struggling for it, his status will not be that of ruler but of public enemy, and it will be lawful to kill him as an act of war, provided the conditions of a just war are present (see 1384).
1825. Judges and Executioners in Canon Law.—According to the law of the Church (Canon 984, nn. 6, 7), those who pass the death sentence as judges and the executioners and their immediate and voluntary helpers become irregular (i.e., incapable of lawfully receiving Orders or of exercising their powers). The reasons for this ancient discipline are chiefly two:
(a) clerics are the ministers of Christ, and therefore they should be like their High Priest, whose sacrifice they offer at the altar. Now Christ “when He was reviled, did not revile, when He suffered, He threatened not, but delivered Himself to him that judged Him unjustly” (I Peter, ii. 23). Hence, it is unbecoming that clerics should condemn to death or kill their fellow-men, even criminals;
(b) clerics are the ministers of the New Testament, and therefore they should conform themselves to its spirit of mildness. The divine law itself declares that a bishop should not have private quarrels or inflict blows (I Tim., iii. 3), but the church law goes further and declares that a cleric should not even act as public judge or executioner in capital cases. The Old Testament inflicted corporal punishments and death, and hence we read that its priests and levites put sinners to death with their own hands (Exod., xxxii. 28; Num., xxv. 7, 8; I Kings, xv. 33; III Kings, xviii. 40; I Mach., ii. 24), but the law of Christ contains no sentences of death or of bodily chastisement.
1826. The Right of Self-Defense.—The second case of lawful homicide mentioned above (1819) is the killing of an unjust aggressor, not intended by the slayer, but consequent on his defense of his life against the aggressor. This right of self-defense is granted by natural law itself, and has been denied by but few moralists.
(a) Thus, nature inclines man to prefer his own life to that of another, other things being equal, and therefore it authorizes him to defend his life even at the cost of an aggressor’s life. Even the brute animals are armed by nature to defend themselves against attack.
(b) The natural law also permits one to perform an act from which two effects will follow, one good and the other bad, provided the good effect alone is intended and there is a sufficient reason for permitting the evil effect (see 104). In the present case the killing of the aggressor is an evil, while the protection of the innocent party is a good; but it is only the protection that is intended, and the killing is not an extreme measure in view of the greatness of the good that is at stake.
1827. The right of self-defense is also sanctioned by human laws. (a) Thus, church law recognizes this right in the words of Innocent III: “All laws permit one to repel force by force, but the defense must not be immoderate, nor exercised from desire of revenge.” According to the Code (Canon 985, n. 4) irregularity arises from voluntary homicide, but this does not include the case of lawful self-defense, although a provisional dispensation must be asked for. A cleric has the right of self-defense, as well as a layman. (b) Civil law also has always admitted the right of a person assailed by another to defend himself, even by killing the assailant, if there is no other alternative.
1828. Conditions for the Exercise of This Right.—(a) The assault must be a true aggression (i.e., an act of violence threatening the life of the person assaulted) and unjust (i.e., an attack made without public authority); (b) the resistance must be true self-defense (i.e., an act used to ward off attack or to make the assailant powerless) and moderate (i.e., the person attacked must not use more force than necessary and he must not intend to kill the assailant).