A: The Fifth Commandment, Thou shalt not kill, forbids us to kill, strike, wound or do any other bodily harm to our neighbor, either of ourselves or by the agency of others; as also to wish him evil, or to offend him by injurious language. In this Commandment God also forbids the taking of one's own life, or suicide.
A: Because the slayer unjustly invades the right which God alone has over the life of man; because he destroys the security of civil society; and because he deprives his neighbor of life, which is the greatest natural good on earth.
A: It is lawful to kill when fighting in a just war; when carrying out by order of the Supreme Authority a sentence of death in punishment of a crime; and, finally, in cases of necessary and lawful defense of one's own life against an unjust aggressor.
A: Yes, in the Fifth Commandment God also forbids us to do harm to another's spiritual life by scandal.
A: Scandal is any word, act, or omission which is the occasion of another's committing sin.
A: Scandal is a grave sin because, by causing the loss of souls, it tends to destroy the greatest work of God, namely, the redemption; it effects the death of another's soul by depriving it of the life of grace, which is more precious than the life of the body; and is the source of a multitude of sins. Hence God threatens the severest chastisement to those who give scandal.
A: In the Fifth Commandment God forbids suicide, because man is not the master of his own life no more than of the life of another. Hence the Church punishes suicide by deprivation of Christian burial.
A: Yes, dueling is also forbidden by the Fifth Commandment, because dueling has in it the guilt both of suicide and of homicide; and whoever voluntarily takes part in it, even as a simple onlooker, is excommunicated.
A: This sort of dueling is also forbidden, because not only are we forbidden to kill, but even voluntarily to wound ourselves or others.
A: No, because it is not true that the offense is repaired by dueling; and because honor cannot be repaired by an unjust, irrational and barbarous act such as dueling.
A: The Fifth Commandment commands us to forgive our enemies and to wish well to all.
A: He who has injured another must not only confess his sin, but must also repair the harm by compensating his neighbor for the loss he has sustained, by retracting the errors taught, and by giving good example.