It is normal today to defend the right of one state to make war against another by comparing a war against aggression with a private individual’s exercise of his right of self-defence. If I have a right to live, it seems that I must have a right to protect my life against violent and unjust attack; it is probable that in order effectively to protect myself I may have to use violence, even such as to cause the death of the aggressor in a case of extreme necessity. If an individual can do this, then clearly an organized group can do the same, and this implies the use of an army by a state. Such an army would be used as an individual uses his fists or his sword or his gun in a lawless land; it would be used to protect the life of the country in an internationally lawless world.

Such is the commonsense approach to the justification of war today; and such, if we make allowances for the lack of theological refinement, is the current Catholic view of the just war. It depends for its cogency on an extension of the rights of the individual to the rights of the state.

It may cause some surprise, therefore, to those who regard Saint Augustine as the main source of the just war tradition to find that not only is such a line of reasoning absent from his writings, but that it is in fact directly contrary to his teaching.

In his treatise on Freewill, he states clearly that an individual has no moral right to kill an assailant in defence of life, liberty or honour. A law permitting such killing may well be objectively reasonable, since it permits the lesser of two evils; it is a lesser evil for a robber to be killed than for a good man to be killed.