Suppose two swimmers, Peter and Paul, are trying to save Thomas, who dies in the water; as he dies Thomas grips Peter and Paul so tightly that they cannot shake the corpse off. Peter is weak, and he will soon sink and drown, owing to his weakness and the weight of the corpse; Paul also will go down later, owing to the weight of Peter and Thomas. Peter, however, cuts his own clothing loose from the grip of the corpse and is saved; but Paul immediately is drowned, owing to the fact that the full weight of the corpse comes upon him. Is Peter justified in cutting himself loose? Certainly he is. This is an example of indirect killing, a case of double effect, one good, the saving of Peter's life, the other evil, the loss of Paul's life, both proceeding immediately and equally from the causal act, the cutting loose of the clothing. The good effect is intended, the bad effect is reluctantly permitted. Again, let us set the same condition for Peter, Paul, and Thomas; but Peter is not able to cut himself loose. John, a fourth person, can cut Peter loose and save him, but can do no more; he must let Paul go down with the corpse of Thomas. May John cut Peter loose? Certainly he may, on the principle _quod liceat per se licet per alium_. This is another case of double effect, with the extenuating circumstances as above. Suppose, however, Peter represents a living infant in the womb of Ann, and that she is in labor; further, this infant cannot be delivered owing to the contraction of Ann's pelvis. May John, a physician, cut away Peter by craniotomy and so save Ann's life? Certainly he may _not_. John here _directly_ brains Peter to save Ann, although Peter is not an unjust aggressor; he does a murder to get a good effect, and the end does not justify the means. There are two effects, but the good effect follows from the bad one, and not immediately from the causal act. Take another example: Peter is a swimmer disabled by cramps and about to drown; Paul, going to save Peter, is seized by Peter, and both are now in danger of drowning; John goes to help Peter and Paul. He cannot get Peter's grip loose by ordinary means, and he sees he can save only one man, either Peter or Paul. May John knock Peter senseless to loosen his grip from Paul, bring in Paul, and thus leave Peter to drown? Certainly he may. You have the double effect here also. Moreover, Peter is a materially unjust aggressor; he is like a maniac trying to kill Paul. In the craniotomy case the child is not a materially or formally unjust aggressor, it is not doing anything at all. It is where the mother put it, and it has a full right to its position and its life. John most probably might also knock Paul senseless and save Peter, if through affection or similar motive he preferred this course. He would then be justified by the double-effect principle alone, although Paul is in no sense an aggressor. The intention of the blow would have to be solely to loosen Paul's hold.