Justice consists simply in respecting the personality of others. This is a straightforward application of the moral law. The only way to respect the personality of another person is to treat him never as a means but always as an end. Others, like ourselves, have both a body and a soul, and we should respect these in the same way we respect our own. To respect the body of another is to do nothing to undermine his life. “Thou shalt not kill” is the first formula of the duty of justice. While this formula seems to be among the most absolute of all morality, there are exceptions to it. If all men followed the moral law perfectly, of course, exceptions would be unnecessary. But this isn't the case, for there are men who constantly threaten others and remain outside the bounds of morality. The result is a state of war, which exists wherever there are criminals, more or less powerful men who consider themselves above the law. In other words, a state of war can exist regardless of whether or not nations attack each other. When dealing with criminals, the moral law no longer applies and must be altered. All the valid exceptions to this law have the following form: “All men whose lives are threatened have the right to defend themselves and, if necessary, to go so far as to kill their aggressor.” This is the right of self-defense.