Question — Merkelbach, Summa Theologiae Moralis

Question Three: On the Killing of One's Neighbor

¶1.

S. Th. II-II, q. 64, a. 2, 3, 4, 6, 7, 8.

355.

355. The killing of one's neighbor, like the killing of oneself, is distinguished as direct and indirect. Direct killing is not just, except from public authority, toward malefactors, and toward harmful enemies in a just war, but not toward the innocent, nor for merely private persons; nevertheless indirect killing can be licit, even for merely private persons, for the sake of just defense or preservation.

355.

The unjust killing of a man is called homicide, that is, the slaughter of a man; but this is simple, or qualified, that is, involving a specially sinful circumstance to be declared in confession, for example, sacrilegious homicide (by reason of a sacred person), parricide, fratricide, killing of a spouse, infanticide or the slaughter of offspring, regicide, robbery perpetrated from the will of plundering, assassination or homicide done from compact or from ambush.

356.

356. Thesis I. From natural law, supposing the natural fact of society, the supreme civil authority can punish by capital penalty malefactors fully convicted of a most grave crime, as often as the public good requires this.

356.

Thus against the Waldenses and Anabaptists, and against certain modern philosophers, who unduly restrict that right to the crime of sedition or even assert that it is altogether useless and unjust, because an aggressor is indeed justly killed while in act, but one captured is no longer able to harm; or because authority is derived from the social pact, but individuals reserve for themselves the right to life, which they cannot renounce: thus among others Cesare Beccaria, Jeremy Bentham, Ch. Lucas, Spedalieri, Ahrens, Holtzendorff.

356.

It is certain from the profession of faith by Innocent III against the Waldenses: "Concerning secular power we assert that without mortal sin it can exercise the judgment of blood."

356.

It is proved 1) by reason: To the supreme social power there belongs the right and office of defending laws by efficacious sanctions and of efficaciously deterring malefactors from crimes: for this is necessary to the good of the republic. But for the most part it could not sufficiently furnish this, unless it threatened capital punishment and inflicted it, as is established by experience: both historical experience, from the common estimation of all times, and psychological, because many men are found who are not sufficiently moved by other penalties of exile or detention, even perpetual, whether laborious or solitary, but for whom the penalty of death is the one remedy which of itself efficaciously detains them from every crime. Therefore the supreme social power has the right of inflicting capital punishment.

356.

And indeed: a) Supposing that in society there is present the power of punishing, as cannot be denied, it is required that the moral order violated in the republic be sufficiently repaired, and crimes be punished by proportionate penalties. But some crimes are so grave that they can be expiated only by capital punishment and abscission from human society; therefore.

356.

b) Right reason dictates that a part is to be amputated if it harms the whole. As St. Thomas teaches, q. 64, a. 2: "Every part is ordered to the whole as the imperfect to the perfect; and therefore every part naturally is for the sake of the whole. And on account of this we see that if the cutting off of some member is expedient for the health of the whole human body, say when it is putrid or corruptive of other members, it is laudably and healthfully cut off. But each singular person is compared to the whole community as a part to the whole. And therefore if some man is dangerous to the community, and corruptive of it because of some sin, he is laudably and healthfully killed, so that the common good may be preserved."

356.

Briefly: experience teaches that the one remedy which efficaciously draws back from crimes is capital punishment; without it neither are crimes sufficiently vindicated nor is society sufficiently protected.

356.
  1. Revelation also recognizes this. For the old law established: "You shall not allow malefactors to live... He who strikes and kills a man, let him die by death" (Exod. XXII, 18; Lev. XXIV, 17), of which the universal reason is indicated: "Whoever sheds human blood, his blood shall be shed" (Gen. IX, 6). Whence it holds not only concerning the power instituted among the Jews in the Old Law, but also in the New Testament concerning the supreme power among pagans, as the Apostle testifies (Rom. XIII, 4): "But if you have done evil, fear; for he does not bear the sword without cause: he is the minister of God, an avenger unto wrath against him who does evil."
356.

But it is said: a) it belongs to the supreme social authority: for no one except public power can inflict the penalty of death, because malefactors can licitly be killed only for the common good. "To kill malefactors," says St. Thomas, a. 3, "is licit insofar as it is ordered to the safety of the whole community, and therefore it belongs only to him to whom the care of preserving the community is committed; just as it belongs to a physician to cut off a putrid member, when care of the health of the whole body has been committed to him. But the care of the common good is committed to princes having public authority; and therefore it is licit for them alone to kill malefactors, but not for private persons." Besides, then greater evils would arise for society and perpetual conflicts. Whence it is licit neither for the people (lynching), nor for a father or husband, to kill malefactors, even in the very moment of the crime committed, from indignation, or to kill an adulterer or a daughter or adulterous wife caught in the act of delict; but if civil law sometimes tolerates this, it does not make it licit in conscience but only intends not to punish in the judicial forum, as St. Thomas testifies, IV Sent., d. 37, q. 2, a. 1: "The civil law accounts it as quasi-licit that he kill her (the wife) in the very act (of adultery), not as commanding it, but as not inflicting the penalty of homicide, on account of the very great incitement which the man has in such a deed toward killing his wife. But the Church in this is not bound by human laws... And therefore in no case is it licit for a man to kill his wife by his own authority."1

1 Hence the proposition condemned by Alexander VII, 19: "A husband killing by his own authority a wife caught in adultery does not sin."

356.

b) fully convicted of a most grave crime. Whence it is required that the crime be very grave, morally certain, so indeed that regularly it be judicially established concerning it, and that before death time be given to the guilty person so that he can provide for conscience and eternal salvation. Therefore officers who could not capture or guard a criminal cannot kill him, although they can discharge a firearm into the legs of one fleeing so that he may be captured, even if from this he could accidentally be killed.

356.

c) insofar as the common good requires this. Hence it is not always required that the sin in itself be very grave; it suffices that it greatly harms the republic. "Whence," says Billuart, diss. 10, art. 1, "military laws are not to be called unjust, although they decree the penalty of death for faults light in themselves, say, for brief sleep, for deserting a post, neglecting guard, slight disobedience, a small theft, because from delicts of this kind, however light in themselves, most grave evils would follow for the republic if they were not most severely restrained."

357.

357. Corollaries. - 1. Once the necessity of capital punishment has been proved, by that very fact it is proved that God has conceded such a right to Society. For since He is the author of society, consequently He willed to confer upon it all things necessary; and otherwise we know this positively from revelation.

357.
  1. By that very fact also it is proved that the right of society overcomes the right of a private person to life. In the subordination of rights, the right of society is to be preferred to the right of the individual. Whence the right to life ceases in certain circumstances, and just as society, when the common good urges, can obligate with danger of death, so also can it impose the penalty of death.
357.
  1. A penalty which inflicts irreparable damage, such as the penalty of death, cannot be inflicted unless there is certainty of the delict. Yet infallibility is not required for this, but that certainty which suffices in human acts, so that the delict is morally certain, just as also it suffices for performing a surgical operation. Besides, we are accustomed to do many things which do not infallibly exclude every danger of death.
357.
  1. Nor, in order not to impede the amendment of the delinquent, is the penalty of death always to be omitted. For as St. Thomas notes, C. Gentes, l. III, c. 146: "But that evil men, as long as they live, can be amended, does not prohibit their being able to be killed justly; because the danger which threatens from their life is greater and more certain than the good which is expected from their amendment. They also have in the very article of death the faculty that through penitence they may be converted to God. But if they are so obstinate that even in the danger of death their heart does not recede from malice, it can be judged sufficiently probably that they will never recover from malice." Amendment indeed is a secondary end of penalties; the primary is the common good to be vindicated.2

2 Cf. I-II, q. 87, a. 3, ad 2; q. 95, a. 1.

357.
  1. Therefore penalty can be viewed in two ways: before infliction, in threat, and thus it has influence toward deterring from crime; after infliction, in execution, and thus it avails for repairing the order injured in the evil example given to others, and at the same time for impeding new crimes of the guilty person.
358.

358. Observation. - In a just war, from the supreme social authority, on account of the good of the republic, it is licit to kill enemies officially fighting, but not those already captured, or those laying down arms, nor inhabitants unless they exercise acts of hostility. Thus from legal justice (n. 274).

359.

359. Thesis II. Direct killing of the innocent is a most grave sin, injurious not only to God and society, but also to one's neighbor. - It is proved: For by its own nature it contains a threefold injustice:

359.

a) against God, whose dominion it violates, since He is the owner of human life and of the human body; whence it is never licit directly to kill an innocent person, unless God commands;

359.

b) against society, which it unjustly deprives of the utility of one of its members, while it is unwilling;

359.

c) against one's neighbor, whom, while unwilling, it deprives of the use of the greatest temporal good, which is the foundation or condition of every other good.

359.

Whence also it is prohibited by divine law: Exod. XX, 13: You shall not kill; or more explicitly, XXIII, 7: "The innocent and just you shall not kill, because I abhor the impious."

359.

Hence it is unjust: 1) to kill lethally wounded persons, old men, the sick, the dying, lest they suffer longer, or directly to hasten their death; likewise to kill madmen, lest they harm others, unless here and now they cannot otherwise be restrained, for then they are unjust aggressors; or also in shipwreck to cast some companions into the sea so that the rest may be saved;

359.
  1. to kill a mother placed in extremities, so that the infant can be baptized; but she herself, if her life can be hoped for, must undergo the operation so that the infant may be baptized;
359.
  1. to kill ambassadors or hostages, even if the enemies who sent them have not kept given faith, indeed have killed other hostages: for they are innocent;
359.
  1. to kill infants or directly hasten their death from whatever motive;
359.
  1. to ask for or perform puncture of the heart upon a deceased person, namely, to puncture the heart or open an artery in him who is reputed deceased, lest perhaps he be buried alive if death is not entirely certain, because this is to expose oneself to the danger of killing a man.3

3 To the question whether it is licit, by mandate of public authority, directly to kill those who, although they have committed no crime worthy of death, nevertheless on account of psychic or physical defects can no longer benefit the nation, and are judged rather to burden it and to obstruct its vigor and strength, the Holy Office recently responded: In the negative, since it is contrary to natural right and positive divine right (27 Nov. - 2 Dec. 1940).

360.

360. Thesis III. Indirect killing generally is not licit, unless from a just and proportionately grave cause, that is, from a greater good which immediately follows from the action and not by means of the killing.

360.

It is proved: For it is not licit to cause an evil effect, the death of another, unless the cause also immediately produces an effect so good that it compensates the evil; as was said in qu. 2, n. 352.

360.

Hence 1) it is not illicit: in a just war to direct engines of war against a besieged city, although many innocent persons perhaps are killed, provided that it is an efficacious means for attacking the city; to give a necessary medicine to a pregnant mother, although perhaps abortion and the death of the fetus follow; to pierce through an innocent child whom an unjust aggressor has placed before himself lest he be wounded, because the unjust aggression redounds upon the child, indeed, according to some, to flee through a narrow way, while an enemy is pursuing, with danger of trampling a child (if that child has been baptized); but otherwise if the danger of death were from a just cause or from a natural cause such as fire.

360.
  1. On the contrary it is illicit for a physician, for the sake of experiment, to use a new remedy or perform a dangerous operation, when a more efficacious and less rash remedy is at hand; likewise to throw a child before pursuing wolves, who otherwise would devour several others, or to cast some into the sea for lightening a boat otherwise to be sunk, unless those who were last to go down into it are the cause why it is to be sunk: for these alone are harmful; the rest are innocent.
360.
  1. It is licit, for sparing a city, to hand over an innocent person whose life a tyrant or enemy demands, indeed even to command him himself to hand himself over for the common good; but not to kill him, even if he consents.
361.

361. Thesis IV. The killing of an unjust aggressor, at least indirect, is licit for defending life or an equivalent good, with the moderation of blameless defense being observed.

361.

It is said 1) licit, and not obligatory, because generally no one is bound to defend himself in this hard way, but he can, from a motive of virtue, permit his own death, unless he is very necessary to his family or to the common good, or unless he distrusts his own state of grace;4

4 Let it not be said that he who offers his life for his neighbor is always in the state of grace, because he performs an act of heroic charity; for that is true only if he so acts from the motive of perfect love of God.

361.
  1. the killing of an aggressor, that is, of one who actually brings force to bear, or at least in some way has begun the work and morally is already invading, as if he displays signs of an imminent aggression (by drawing a sword, seizing a firearm, etc.), or has altogether determined to attack and is now seeking the occasion of aggression and this is established from some present indication; but in doubt there would be place for caution or for interrogation, not for defense.5 For to kill before the aggression would be to forestall it, not to defend oneself against it; and when the aggression has ended, it would no longer be defense, but vengeance;

5 Hence Alexander VII condemned proposition 18: "It is licit to kill a false accuser, false witnesses, even a judge, from whom an unjust sentence is certainly imminent, if in no other way can an innocent person avoid harm."

361.
  1. unjust; therefore it is illicit to defend oneself against the just action of ministers of justice or of officers, but licit against a materially unjust aggression attempted by a drunken man or a madman, unless that man certainly is in the state of sin and the one attacked is certainly in the state of grace;
361.
  1. at least indirect: we say this because some, such as Lugo and Waffelaert, think that in the case the direct killing itself is licit, provided that it is not intended as an end but chosen as a means; nevertheless we judge it more conformable to truth, with St. Thomas, that bloody defense is nothing except indirect killing;
361.
  1. for defending life or an equivalent good, whether one's own or another's, so that there is present a good effect proportionate to the death of the aggressor; but an equivalent good is the integrity of members to be preserved, or sensation or the use of reason not to be irreparably lost: whether another good can be judged equivalent is left aside for now;
361.
  1. with the moderation of blameless defense, that is, so that no more be done than is necessary for defense; whence it is illicit to kill if it suffices to wound, illicit to wound if it suffices to shout, or if it is possible to flee without dishonor, but not if it would be done with great detriment: a soldier or nobleman cannot always flee without dishonor; a cleric, a man of the common people can; indeed a soldier or nobleman can before a madman or a drunken man.
361.

It is proved: It is licit to posit a cause of a double effect, one good, the other evil, when certain conditions are present (n. 352). But this is verified in the case. For a) the indirect killing of an unjust aggressor is an action not evil, since it is nothing except to repel force by force and just defense; b) from it there equally and immediately arises the good effect, namely the preservation of life, just as the evil: the death of the aggressor; c) the good effect is proportionate to the evil, because the life of the innocent one attacked is worth the life of the guilty aggressor, and it is not otherwise to be preserved; d) only the good effect is intended in itself, not thus the evil, since if it could be done otherwise it would not be inflicted. Therefore it is licit.

361.

This was solemnly consecrated by the Law, as Innocent III relates: "Although all laws and rights permit force to be repelled by force, nevertheless, because this must be done with moderation of blameless defense, not for taking vengeance but for driving away injury..."6

6 Cf. French Penal Code, a. 328; Belgian, a. 416; German, a. 53; likewise English law.

361.

Let St. Thomas be heard, q. 64, a. 7: "Nothing prohibits there being two effects of one act, of which one only is in the intention, while the other is outside the intention... Therefore from the act of someone defending himself a double effect can follow: one indeed, the preservation of his own life; but the other, the killing of the attacker. Therefore an act of this kind, from the fact that the preservation of one's own life is intended, does not have the character of the illicit, since this is natural to anyone, that he preserve himself in being as much as he can. Yet some act proceeding from a good intention can be rendered illicit if it is not proportionate to the end. And therefore if someone, for defending his own life, uses greater violence than is fitting, it will be illicit. But if he repels violence moderately, the defense will be licit, for according to the laws 'it is licit to repel force by force with the moderation of blameless defense.' Nor is it necessary for salvation that a man omit an act of moderate defense in order to avoid the killing of another, because a man is bound to provide for his own life more than for another's life. But because it is not licit to kill a man except by public authority on account of the common good..., it is illicit that a man intend to kill a man in order to defend himself, unless he is one who has public authority; and he, intending to kill a man for his own defense, refers this to the public good, as is clear in a soldier fighting against enemies, and in a minister of a judge fighting against robbers, although even these sin if they are moved by private passion."

362.

362. For protecting what goods is bloody defense licit? - Theologians have disputed whether such indirect wounding or killing of an aggressor can be licit for defending other lesser goods of oneself or of another: goods of fortune, chastity, reputation and honor. Now:

362.

But this certainly does not hold a) for goods to be possessed and for a right to the thing, as moreover is established from the condemned proposition 32 by Innocent XI,7 but at most for goods actually possessed and for a right in the thing; b) nor for goods of lesser moment, for example, formerly for one or another gold coin,8 or now for 500 lire or 1,000 francs, even of gold value, but at most for goods of great value; but a matter of great moment would be to fall from one's state, or to suffer great detriment in it, whence it must be considered not only absolutely but relatively; c) nor for those things which could also be recovered otherwise... For goods of great moment, already possessed, whose loss would probably be irreparable, this can be sustained as probable, because it pertains to public security and to the common good that violent robbers should not be able to snatch goods of this kind with impunity, without incurring danger to life. Yet this is not certain, because, as others say: it is not licit as punishment, because punishment does not belong to private persons; nor as defense, because proportion is lacking between the fortune of the attacked one to be preserved and the very life of the attacker.

7 "Not only is it licit to defend by lethal defense the things which we actually possess, but also those to which we have an inchoate right and which we hope that we will possess."

8 Proposition 31 condemned by Innocent XI: "Regularly I can kill a thief for the preservation of one gold coin."

362.

But this also is very doubtful. For the integrity of the flesh does not seem of such value that it can be equated with life. But the integrity of the soul can be preserved otherwise, by not consenting to sin.

362.
  1. Some also have held it licit for defending reputation and honor, which are esteemed more than goods of fortune, indeed more than life.
362.

But this last is true of the foundation of honor, namely, of virtue, which is worth more than life, not of honor itself, which is a very fragile thing. Moreover reputation and honor cannot be defended by the wounding or killing of one defaming or dishonoring. For after the fact, it would not be defense but vengeance by private authority: for if a nobleman who has unjustly received a slap or an insult strikes back, this certainly does not avail for defending honor thus taken away, but for obtaining from vengeance a new and false honor. But before the fact, it would be prevention, not defense; nor is that necessary, because the loss of honor and reputation is not irreparable, since by other means it can be preserved or at least recovered (for example, by verbal retort, by judicial way, or by goodness of life), and the wounding or killing of the attacker is of itself an inept means for conserving or recovering such a good, since it is rather defamatory. Therefore this was deservedly condemned.9 Besides, violent defense of honor or reputation would afford an entrance to countless slaughters and enmities with great detriment to the common good.

9 Proposition 30 condemned by Innocent XI: "It is lawful for an honorable man to kill an attacker who endeavors to bring calumny upon him, if otherwise this disgrace cannot be avoided; the same also must be said if someone gives a slap or strikes with a staff, and after the slap has been given or the blow of the staff flees." And proposition 17 condemned by Alexander VII: "It is licit for a religious and a cleric to kill a calumniator threatening to scatter grave crimes about him or about his religion, when another way of defending is not available; as it does not seem to be available if the calumniator is prepared publicly and before very grave men to impute the aforesaid things either to the religious himself or to his religion, unless he is killed."

362.

All the aforesaid things are to be understood of these goods alone; but it would have to be said otherwise if at the same time there were an aggression against the person, especially if bodily integrity came into danger or an aggression against life could deservedly be feared. For someone can defend his own things (or chastity) even by force, and if the aggressor resists and seriously threatens mutilation or death, he can kill him by necessity of defense. And if one attempts to strike with a slap or a staff, the other can impede him by force; and if he who has struck is prepared to continue the injury, the one attacked can repel force by force (if there is no place for flight), even with the killing of the aggressor when he threatens death.

363.

363. Corollaries. - 1. Especially illicit are embryotomy and the direct procurement of abortion, namely, a) to kill the fetus in the womb in order to save the mother; b) to cast the fetus out of the womb, for that reason soon to die; c) to divide the fetus into parts. - For it is directly to destroy human life, or at least directly to impede it in a subject which is not an unjust aggressor.10 This, for the same reason, holds concerning ectopic or extrauterine fetuses.11

10 Holy Office, 19 Aug. 1889, 24 July 1895, 31 May 1884. - Cf. our Questions on Embryology A, q. 4 and 5; B, q. 2 and 3. Some at one time judged feticide licit, such as Ballenni, Avanzini, Constantini, or abortion, as even Lehmkuhl himself.

11 Holy Office, 4 May 1898 and 5 May 1902. Cf. Questions on Embryology A, q. 7; and B, q. 4. Some try to elude the responses of the Holy Office.

363.

For it is a question of the life of an innocent person, which is equally sacred in a little infant and in an adult mother; whence no reason making the act honorable is present: neither the social power of protecting the common good against crimes, nor legitimate defense against aggression, nor the extreme necessity of the mother.

363.

As Pius XI most recently sanctioned in the encyclical Casti connubii, 31 Dec. 1930: "What cause could ever avail in any way to excuse the direct killing of an innocent person? For this is what is at issue in this place. Whether it is inflicted upon the mother or upon the offspring, it is against the precept of God and the voice of nature: You shall not kill. For the life of each is an equally sacred thing, for the crushing of which there can ever be no faculty, not even to public authority. a) Most ineptly, moreover, is this repeated against the innocent from the right of the sword, which has force only against the guilty; b) nor does any right of bloody defense here prevail against an unjust aggressor, for who would call an innocent little child an unjust aggressor?; c) nor is there present any right of extreme necessity, as they call it, which could reach even to the direct killing of an innocent person."

363.
  1. On the contrary, abortion indirectly procured can be licit, if a) there is present in the mother a lethal disease, b) the means employed is immediately efficacious for curing the mother even when not pregnant, c) no other remedy is present, and d) provision is made for the Baptism of the infant. A fortiori, acceleration of birth can be licit if the infant can live outside the mother's womb, and a grave reason is present.
363.

An action, namely, one bringing danger of death and directly affecting the fetus itself, or some organ or element pertaining to it, such as the placenta, the membranes enveloping it, or the amniotic fluid, cannot be legitimized by the fact that it is necessary for saving the mother, because it immediately harms only the offspring and procures the good of the mother only by means of the evil of the offspring, and thus is directly harmful and lethal; - on the contrary an action which is exercised not directly upon the fetus, nor upon any instrument or element of it, but upon the mother or an organ of the mother, say upon the uterus or tube, can be licit, provided that a) it directly procures the good of the mother, b) it is necessary here and now for saving her life, c) the danger does not proceed from the fetus alone.

363.
  1. Concerning accidental homicide, St. Thomas teaches, art. 8: He who posits an action from which, accidentally and not of itself, frequently and probably, death follows, is not guilty of homicide, provided that he has used ordinary solicitude: thus a hunter, by employing due diligence, accidentally kills a man. On the contrary, per accidens he can be guilty of homicide "who does not remove those things from which homicide follows, if he ought to remove them." This happens in two ways: a) if he is guilty of negligence, not employing due diligence, for example, by imprudently playing with a firearm, and then he sins gravely or lightly according as the negligence is grave or light: thus imprudent pregnant women, and physicians negligent in caring for the sick; b) if the action of itself is unjust and includes danger of homicide, for example, by striking a pregnant woman, or by employing dangerous materials or machines from which the life of workers is placed in great danger.
364.

364. Remarks. - 1st. As with the killing of oneself, so also with the killing of an innocent person, in practice it is not always easy to determine whether it is direct or indirect; whence here also the first remark made in the preceding article, n. 354, 1st, must be applied.

364.

2nd. For practice we note that the probable doctrine concerning the killing of an unjust aggressor against chastity or goods of fortune is not to be publicly proposed to the people, on account of the abuses which would easily follow from it. In fact, that doctrine can very rarely be brought into practice, because a thief can ordinarily be repelled by other means, and because a thing seized can often be sought back by judicial way.

364.

Besides, our Penal Code (arts. 416 and 417) does not recognize a right of defense unless the aggression is in some way judged to be directed against the person.

364.

3rd. Charity does not require that one abstain from killing a culpable aggressor in order to avoid his eternal damnation. Charity indeed obliges even to exposing one's own life if one's neighbor is in extreme spiritual necessity. But a culpable aggressor is not in extreme necessity, since he voluntarily exposes his salvation and, by giving up the unjust aggression, can escape unharmed.

364.

4th. Just as someone can protect himself by bloody defense, so also from charity he can, for the defense of his neighbor, do what that person can do for himself; but he could not thus defend goods which the neighbor voluntarily renounces, for example, the chastity of a woman who consents to sin or does not resist. Yet no one is bound thus to defend his neighbor, unless a special office obliges him to this, as officers, or piety or the common good urges, for example, for the life of a father or of a person who is altogether necessary to the republic.

364.

5th. It is illicit to kill a legitimate prince, though a tyrant by regime and oppression, because no one can, unless he has public authority, kill a malefactor however distinguished; - unless the people, in establishing the king, reserved to itself this power of punishing in this way, or unless it is a question of necessary defense against an actual unjust aggression.

364.

But a usurper or tyrant by title, who has not yet become the legitimate king, can be killed, apart from the case of just defense, by the authority of the legitimate prince or in an act of war of the republic against him, if he does not yet possess the kingdom peacefully; but if he now possesses it, this can be done only from the authority of the legitimate prince commanding it. - In practice, however, it will not be licit unless certain conditions have been posited, namely, a) that the tyrant certainly does not have a right to the kingdom; b) that there likewise is no superior to whom recourse can be had; c) that the republic does not contradict the killing of the tyrant; d) and that from his killing more or greater evils are not to be expected.12

12 Thus Billuart, diss. X, a. 2.