On Murder

St. Thomas Aquinas

Whether it is unlawful to kill any living thing?

Objection 1. It would seem unlawful to kill any living thing. For the Apostle says (Rom. 13:2): “They that resist the ordinance of God purchase to themselves damnation [Vulg.: ‘He that resisteth the power, resisteth the ordinance of God: and they that resist, purchase themselves damnation.’].” Now Divine providence has ordained that all living things should be preserved, according to Psalms 146:8,9, “Who maketh grass to grow on the mountains . . . Who giveth to beasts their food.” Therefore it seems unlawful to take the life of any living thing.

Objection 2. Further, murder is a sin because it deprives a man of life. Now life is common to all animals and plants. Hence for the same reason it is apparently a sin to slay dumb animals and plants.

Objection 3. Further, in the Divine law a special punishment is not appointed save for a sin. Now a special punishment had to be inflicted, according to the Divine law, on one who killed another man’s ox or sheep (Ex. 22:1). Therefore the slaying of dumb animals is a sin. On the contrary, Augustine says (City of God, I.20): “When we hear it said, ‘Thou shalt not kill,’ we do not take it as referring to trees, for they have no sense, nor to irrational animals, because they have no fellowship with us. Hence it follows that the words, ‘Thou shalt not kill’ refer to the killing of a man.”

I answer that, There is no sin in using a thing for the purpose for which it is. Now the order of things is such that the imperfect are for the perfect, even as in the process of generation nature proceeds from imperfection to perfection. Hence it is that just as in the generation of a man there is first a living thing, then an animal, and lastly a man, so too things, like the plants, which merely have life, are all alike for animals, and all animals are for man. Wherefore it is not unlawful if man use plants for the good of animals, and animals for the good of man, as the Philosopher states (Aristotle, Politics, I.3).

Now the most necessary use would seem to consist in the fact that animals use plants, and men use animals, for food, and this cannot be done unless these be deprived of life: wherefore it is lawful both to take life from plants for the use of animals, and from animals for the use of men. On fact this is in keeping with the commandment of God Himself: for it is written (Gen. 1:29,30): “Behold I have given you every herb . . . and all trees . . . to be your meat, and to all beasts of the earth”: and again (Gen. 9:3): “Everything that moveth and liveth shall be meat to you.”

Reply to Objection 1. According to the Divine ordinance the life of animals and plants is preserved not for themselves but for man. Hence, as Augustine says (City of God, I.20), “by a most just ordinance of the Creator, both their life and their death are subject to our use.”

Reply to Objection 2. Dumb animals and plants are devoid of the life of reason whereby to set themselves in motion; they are moved, as it were by another, by a kind of natural impulse, a sign of which is that they are naturally enslaved and accommodated to the uses of others.

Reply to Objection 3. He that kills another’s ox, sins, not through killing the ox, but through injuring another man in his property. Wherefore this is not a species of the sin of murder but of the sin of theft or robbery.

Whether it is lawful to kill sinners?

Objection 1. It would seem unlawful to kill men who have sinned. For our Lord in the parable (Mt. 13) forbade the uprooting of the cockle which denotes wicked men according to a gloss. Now whatever is forbidden by God is a sin. Therefore it is a sin to kill a sinner.

Objection 2. Further, human justice is conformed to Divine justice. Now according to Divine justice sinners are kept back for repentance, according to Ezekiel 33:11, “I desire not the death of the wicked, but that the wicked turn from his way and live.” Therefore it seems altogether unjust to kill sinners.

Objection 3. Further, it is not lawful, for any good end whatever, to do that which is evil in itself, according to Augustine (Contra Mendac. VII) and the Philosopher (Ethics II.6). Now to kill a man is evil in itself, since we are bound to have charity towards all men, and “we wish our friends to live and to exist,” according to Ethic. ix, 4. Therefore it is nowise lawful to kill a man who has sinned.

On the contrary, It is written (Ex. 22:18): “Wizards thou shalt not suffer to live”; and (Ps. 100:8): “In the morning I put to death all the wicked of the land.”

I answer that, As stated above (1), it is lawful to kill dumb animals, in so far as they are naturally directed to man’s use, as the imperfect is directed to the perfect. Now every part is directed to the whole, as imperfect to perfect, wherefore every part is naturally for the sake of the whole. For this reason we observe that if the health of the whole body demands the excision of a member, through its being decayed or infectious to the other members, it will be both praiseworthy and advantageous to have it cut away. Now every individual person is compared to the whole community, as part to whole. Therefore if a man be dangerous and infectious to the community, on account of some sin, it is praiseworthy and advantageous that he be killed in order to safeguard the common good, since “a little leaven corrupteth the whole lump” (1 Cor. 5:6).

Reply to Objection 1. Our Lord commanded them to forbear from uprooting the cockle in order to spare the wheat, i.e. the good. This occurs when the wicked cannot be slain without the good being killed with them, either because the wicked lie hidden among the good, or because they have many followers, so that they cannot be killed without danger to the good, as Augustine says (Contra Parmen. III.2). Wherefore our Lord teaches that we should rather allow the wicked to live, and that vengeance is to be delayed until the last judgment, rather than that the good be put to death together with the wicked. When, however, the good incur no danger, but rather are protected and saved by the slaying of the wicked, then the latter may be lawfully put to death.

Reply to Objection 2. According to the order of His wisdom, God sometimes slays sinners forthwith in order to deliver the good, whereas sometimes He allows them time to repent, according as He knows what is expedient for His elect. This also does human justice imitate according to its powers; for it puts to death those who are dangerous to others, while it allows time for repentance to those who sin without grievously harming others.

Reply to Objection 3. By sinning man departs from the order of reason, and consequently falls away from the dignity of his manhood, in so far as he is naturally free, and exists for himself, and he falls into the slavish state of the beasts, by being disposed of according as he is useful to others. This is expressed in Psalms 48:21: “Man, when he was in honor, did not understand; he hath been compared to senseless beasts, and made like to them,” and Proverbs 11:29: “The fool shall serve the wise.” Hence, although it be evil in itself to kill a man so long as he preserve his dignity, yet it may be good to kill a man who has sinned, even as it is to kill a beast. For a bad man is worse than a beast, and is more harmful, as the Philosopher states (Politics I.1 and Ethics VII.6).

Whether it is lawful to kill the innocent?

Objection 1. It would seem that in some cases it is lawful to kill the innocent. The fear of God is never manifested by sin, since on the contrary “the fear of the Lord driveth out sin” (Sirach 1:27). Now Abraham was commended in that he feared the Lord, since he was willing to slay his innocent son. Therefore one may, without sin, kill an innocent person.

Objection 2. Further, among those sins that are committed against one’s neighbor, the more grievous seem to be those whereby a more grievous injury is inflicted on the person sinned against. Now to be killed is a greater injury to a sinful than to an innocent person, because the latter, by death, passes forthwith from the unhappiness of this life to the glory of heaven. Since then it is lawful in certain cases to kill a sinful man, much more is it lawful to slay an innocent or a righteous person.

Objection 3. Further, what is done in keeping with the order of justice is not a sin. But sometimes a man is forced, according to the order of justice, to slay an innocent person: for instance, when a judge, who is bound to judge according to the evidence, condemns to death a man whom he knows to be innocent but who is convicted by false witnesses; and again the executioner, who in obedience to the judge puts to death the man who has been unjustly sentenced.

On the contrary, It is written (Ex. 23:7): “The innocent and just person thou shalt not put to death.”

I answer that, An individual man may be considered in two ways: first, in himself; secondly, in relation to something else. If we consider a man in himself, it is unlawful to kill any man, since in every man though he be sinful, we ought to love the nature which God has made, and which is destroyed by slaying him. Nevertheless, as stated above (2) the slaying of a sinner becomes lawful in relation to the common good, which is corrupted by sin. On the other hand the life of righteous men preserves and forwards the common good, since they are the chief part of the community. Therefore it is in no way lawful to slay the innocent.

Reply to Objection 1. God is Lord of death and life, for by His decree both the sinful and the righteous die. Hence he who at God’s command kills an innocent man does not sin, as neither does God Whose behest he executes: indeed his obedience to God’s commands is a proof that he fears Him.

Reply to Objection 2. In weighing the gravity of a sin we must consider the essential rather than the accidental. Wherefore he who kills a just man, sins more grievously than he who slays a sinful man: first, because he injures one whom he should love more, and so acts more in opposition to charity: secondly, because he inflicts an injury on a man who is less deserving of one, and so acts more in opposition to justice: thirdly, because he deprives the community of a greater good: fourthly, because he despises God more, according to Luke 10:16, “He that despiseth you despiseth Me.” On the other hand it is accidental to the slaying that the just man whose life is taken be received by God into glory.

Reply to Objection 3. If the judge knows that man who has been convicted by false witnesses, is innocent he must, like Daniel, examine the witnesses with great care, so as to find a motive for acquitting the innocent: but if he cannot do this he should remit him for judgment by a higher tribunal. If even this is impossible, he does not sin if he pronounce sentence in accordance with the evidence, for it is not he that puts the innocent man to death, but they who stated him to be guilty. He that carries out the sentence of the judge who has condemned an innocent man, if the sentence contains an inexcusable error, he should not obey, else there would be an excuse for the executions of the martyrs: if however it contain no manifest injustice, he does not has no right to discuss the judgment of his superior; nor is it he who slays the innocent man, but the judge whose minister he is.

Thomas Aquinas (1225-1274), Doctor and Saint of the Catholic Church, was an Italian philosopher and theologian.

This passage was excerpted from Summa Theologica, Second Part of the Second Part, Question 64. “On Murder.” The Summa Theologica of St. Thomas Aquinas. 2nd Edition, trans. Fathers of the English Dominican Province, 1920. Full text