"There is nothing to hinder one act having two effects, of which one only is within the intention [and election] of the doer, while the other is beside his intention [and election, that is, is neither intended as an end nor elected as a means].... From the act therefore of one defending himself a twofold effect may follow, one the preservation of his own life, the other the killing of the aggressor. Now such an act, in so far as the preservation of the doer's own life is intended, has no taint of evil about it, seeing that it is natural to everything to preserve itself in being as much as it can. Nevertheless, an act coming of a good intention may be rendered unlawful, if it be not in proportion to the end in view. And therefore, if any one uses greater violence than is necessary for the defence of his life, it will be unlawful. But if he repels the violence in a moderate way, it will be a lawful defence: for according to the Civil and Canon Laws it is allowable _to repel force by force with the moderation of a blameless defence_. Nor is it necessary to salvation for a man to omit the act of moderate defence in order to avoid the killing of another; because man is more bound to take thought for his own life than for the life of his neighbour. But because to kill a man is not allowable except by act of public authority for the common good, it is unlawful for a man to intend [that is, elect and choose as a means] to kill another man in order to defend himself, unless he be one who has public authority, who intending [electing] to kill a man in order to his own defence, refers this to the public good." 2. The right then of self-defence even to the shedding of blood involves a mere exercise of indirect killing for a proportionably grave cause. The cause in question is the defence of your own life, or your friend's, or of some other good or possession that can weigh with life, as the honour and inviolability of your person, or a large sum of money. This must be in present danger of being taken away otherwise than in due course of justice. The danger must be present, and even imminent, not prospective. The right of self-defence even to the grievous harming of the aggressor, endures only while the danger from him is imminent, not when it is past, or the evil is already done. The right supposes no moral obliquity, no formal injustice on the part of the aggressor: he may be a madman making for you with a drawn sword. Nay further, not even _material_ injustice--that is, the quality of an act which would be _formally_ unjust, if only the agent knew what he was about--is required. All that is requisite is that your life, or something equivalent to life, be threatened, _not in due course of law_.