Thomas Aquinas: Summa Theologiae (excerpt, part 7)

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Part II.2, Question 64, Article 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" (Ecclus. 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 (Article [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 Lk. 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 sin by carrying out the sentence, because he 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.

Part II.2, Question 64, Article 7: Whether it is lawful to kill a man in self-defense?

Objection 1: It would seem that nobody may lawfully kill a man in self-defense. For Augustine says to Publicola (Ep. xlvii): "I do not agree with the opinion that one may kill a man lest one be killed by him; unless one be a soldier, exercise a public office, so that one does it not for oneself but for others, having the power to do so, provided it be in keeping with one's person." Now he who kills a man in self-defense, kills him lest he be killed by him. Therefore this would seem to be unlawful.

Objection 2: Further, he says (De Lib. Arb. i, 5): "How are they free from sin in sight of Divine providence, who are guilty of taking a man's life for the sake of these contemptible things?" Now among contemptible things he reckons "those which men may forfeit unwillingly," as appears from the context (De Lib. Arb. i, 5): and the chief of these is the life of the body. Therefore it is unlawful for any man to take another's life for the sake of the life of his own body.

Objection 3: Further, Pope Nicolas says in the Decretals: "Concerning the clerics about whom you have consulted Us, those, namely, who have killed a pagan in self-defense, as to whether, after making amends by repenting, they may return to their former state, or rise to a higher degree; know that in no case is it lawful for them to kill any man under any circumstances whatever." Now clerics and laymen are alike bound to observe the moral precepts. Therefore neither is it lawful for laymen to kill anyone in self-defense.

Objection 4: Further, murder is a more grievous sin than fornication or adultery. Now nobody may lawfully commit simple fornication or adultery or any other mortal sin in order to save his own life; since the spiritual life is to be preferred to the life of the body. Therefore no man may lawfully take another's life in self-defense in order to save his own life.

Objection 5: Further, if the tree be evil, so is the fruit, according to Mt. 7:17. Now self-defense itself seems to be unlawful, according to Rm. 12:19: "Not defending yourselves, my dearly beloved." Therefore its result, which is the slaying of a man, is also unlawful.

On the contrary: It is written (Ex. 22:2): "If a thief be found breaking into a house or undermining it, and be wounded so as to die; he that slew him shall not be guilty of blood." Now it is much more lawful to defend one's life than one's house. Therefore neither is a man guilty of murder if he kill another in defense of his own life.

I answer that: Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental as explained above (Question [43], Article [3]; FS, Question [12], Article [1]). Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists, "it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense." Nor is it necessary for salvation that a man omit the act of moderate self-defense in order to avoid killing the other man, since one is bound to take more care of one's own life than of another's. But as it is unlawful to take a man's life, except for the public authority acting for the common good, as stated above (Article [3]), it is not lawful for a man to intend killing a man in self-defense, except for such as have public authority, who while intending to kill a man in self-defense, refer this to the public good, as in the case of a soldier fighting against the foe, and in the minister of the judge struggling with robbers, although even these sin if they be moved by private animosity.

Reply to Objection 1: The words quoted from Augustine refer to the case when one man intends to kill another to save himself from death. The passage quoted in the Second Objection is to be understood in the same sense. Hence he says pointedly, "for the sake of these things," whereby he indicates the intention. This suffices for the Reply to the Second Objection.

Reply to Objection 3: Irregularity results from the act though sinless of taking a man's life, as appears in the case of a judge who justly condemns a man to death. For this reason a cleric, though he kill a man in self-defense, is irregular, albeit he intends not to kill him, but to defend himself.

Reply to Objection 4: The act of fornication or adultery is not necessarily directed to the preservation of one's own life, as is the act whence sometimes results the taking of a man's life.

Reply to Objection 5: The defense forbidden in this passage is that which comes from revengeful spite. Hence a gloss says: "Not defending yourselves -- that is, not striking your enemy back."

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