3. The essential idea of self-defence is that of stopping a trespasser, one who, however innocently, is going about to trench on that good which you have a right to maintain and reserve to yourself. It is then no act of authority that you perform, but the dealing of one private person with another. Indeed, the party stopped is hardly regarded as a person: no account is taken of his demerits: he is regarded simply as an abridger and diminisher of what you have a right to preserve intact. You stop a man as you stop a horse, only with more regard to _the moderation of a blameless self-defence_, not using more violence than is necessary here and now to preserve what you have to preserve. 4. The stopping, unfortunately, has often to be done in a hurry: there is no time to wait: for the next moment, unless you act promptly, it will be all too late, or all to no purpose, to act at all. Being done in a hurry, it has to be done in a rough-and-ready way, with such instruments as are to hand: you cannot afford to be nice about the means, carefully purifying them, and shaking off the dust of objectionable circumstances. Now to stop a man in mid career all on a sudden, to render him powerless where he was about to strike, motionless in the direction whither he was about to go, and that in an instant, is of common necessity a rude treatment, very dangerous to him who experiences it, and under some conceivable circumstances hopelessly fatal. Still the fatality--in plain words, the death of the aggressor--is not _directly willed_. It is neither _intended_ as an _end_, nor _chosen_ as a _means to an end_. It is not welcomed as an end and desirable consummation: on the contrary, it is put up with most reluctantly as coming from your act: for you, a private individual, have no right to will and effect the death of any man, however guilty, as will be proved hereafter. It is not chosen as a means: for, formally as his death, it is no means to your end, which was the averting of all present danger to your right. For that it was enough to _stop_ the trespasser; and you chose the means as a _stopping_ means, not as a _killing_ means. True, in stopping him you killed him, but you did not kill him to stop him. You struck him to stop him: that your blow was a mortal blow, was a circumstance which you did not choose and could not help. All killing then in self-defence is indirect. 5. By this explanation, resting on St. Thomas--in opposition to Cardinal de Lugo (_De Just. et Jure_. 10, 149) and others, who allow killing in self-defence to be the actual means chosen, and therefore directly willed--we save four grand positions in Moral Science: (a) The axiom, that _it is never lawful directly to take the life of an innocent man_. For the person who perishes by occasion of your defending yourself, may be innocent _formally_, and even _materially_ also.