OF MURDER (EIGHT ARTICLES)
In due sequence we must consider the vices opposed to commutative justice. We must consider (1) those sins that are committed in relation to involuntary commutations; (2) those that are committed with regard to voluntary commutations. Sins are committed in relation to involuntary commutations by doing an injury to one's neighbor against his will: and this can be done in two ways, namely by deed or by word. By deed when one's neighbor is injured either in his own person, or in a person connected with him, or in his possessions.
We must therefore consider these points in due order, and in the first place we shall consider murder whereby a man inflicts the greatest injury on his neighbor. Under this head there are eight points of inquiry:
(1) Whether it is a sin to kill dumb animals or even plants?(2) Whether it is lawful to kill a sinner?
(3) Whether this is lawful to a private individual, or to a public person only?
(4) Whether this is lawful to a cleric?
(5) Whether it is lawful to kill oneself?
(6) Whether it is lawful to kill a just man?
(7) Whether it is lawful to kill a man in self-defense?
(8) Whether accidental homicide is a mortal sin?
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 Ps. 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 (De Civ. Dei 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 (Polit. 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. In 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 ( Gn. 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 (De Civ. Dei 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 ( Mat. 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 Ezech. 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 (Ethic. 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."