1. _Do not kill._ By taking away the life of a human being we should of course cut off all chance of that person's further development. This requires no comment. But certain casuistical questions arise in connection with this command. Is it right to kill another in self-defense? The difficulty involved might be put in this way: A burglar breaks into your house by night and threatens to kill you. You have a weapon at hand and can save yourself by killing him. Now it is evident that one of two lives must be taken. But would it not be more moral on your part to say: I, at least, will not break the commandment. I would rather be killed than kill? This question serves to show to what absurdities a purely formal principle in ethics can lead, as we have already seen in the discussion of truthfulness. The problem of the duel and that of the taking of the life of others in war also belong under this head, but will be reserved for the advanced course. 2. _Respect the personal liberty of others._ Slavery, under whatever form, is an outrage on justice. The slave is degraded to be the mere instrument of his master's profit or pleasure. Let the teacher point out in what particulars the slave is wronged, and show the evil effects of the institution of slavery on the character of the master as well as of the slave. Question--Is it right to speak of wage-slavery, for instance, in cases where the hours of labor are so prolonged as to leave no time for higher interests, or where the relations of the laborer to his employer are such as to impair his moral independence?