Book Fifth. On the Fifth Precept of the Decalogue

¹ "Thou shalt not kill." Ex. 20:13.

This precept is formally negative, prohibiting homicide; but because death can be inflicted both on oneself and on others also by omission of necessary care, the same is virtually also positive. Insofar as it is positive, it commands the preservation of life; but insofar as it is negative, it prohibits primarily indeed the unjust killing both of oneself and of others, but secondarily every unjust injury, whether wounding or mutilation, of one's own or another's life. All these injuries are reduced to homicide, the chief injury of human life. Wherefore there must be treated: a. the preservation of life; b. the killing and mutilation of oneself; c. the killing of a criminal; d. the killing of an unjust aggressor; e. the killing of an innocent person; f. killing in a duel; g. killing in war.

¹ St. Thomas, II-II, q. 64, 65. St. Alphonsus, l. 3, n. 363-411. Lugo, De iustitia et iure, disp. 10. Lessius, De iustitia et iure, l. 2, c. 9. Reuter, Theologia moralis, III, n. 366-386. Sporer-Bierbaum, Theologia moralis decalog., II, tract. 5, n. 150-549. Ballerini-Palmieri, Opus theolog. morale^3, II, n. 848-958. Lehmkuhl, Theologia moralis^10, I, n. 831-859.