On the Fifth Precept of the Decalogue

"Thou shalt not kill." Exod. 20. 13.

388. • This precept, insofar as it is negative, prohibits primarily homicide, that is, the unjust killing of a man; but secondarily and consequently every unjust injury, wounding, or mutilation of the body, whether one's own or another's ¹. But insofar as it is virtually positive, it commands the preservation of life.

¹ Certain divisions of homicide are accustomed to be handed down here, as that one is casual, and another voluntary, and this latter either direct or indirect. But especially homicide simple is to be distinguished from qualified, namely having another species of sin adjoined. Of this sort is: 1. sacrilege, either by reason of the person killed or by reason of the place in which the killing is done; 2. parricide, namely the slaughter either of parents or of children, or of brother or sister, or of a spouse, or even of a Prince; 3. robbery, namely killing or wounding from the will of plundering; 4. magical poisoning, namely when by the aid of the demon bodily evil or even death is brought upon someone.

Also numbered among qualified homicides are customarily: 1. treacherous homicide, namely perpetrated under the appearance of friendship; 2. assassination, both on the part of the hirer to kill and on the part of the one hired; 3. simple poisoning. Yet these distinctions, which some have incautiously transferred as if to diverse moral species, merely serve to measure the gravity of the crime in the external forum; for as regards the forum of conscience, they constitute a merely aggravating circumstance.

Moreover, those things which will be established concerning killing, whether licit or illicit, will have to be applied, with due proportion observed, to mutilation or any injury of the body.

We must treat: 1. of killing oneself; 2. of killing the neighbor; 3. of duel; 4. of war.