Again, the killing of the inviable ectopic fetus cannot be justified by maintaining that the fetus is an unjust aggressor against the life of the mother. An aggressor against life may be such formally or materially. A formally unjust aggressor consciously and voluntarily attacks the life of the victim unjustly. This perversion, or evil, in the aggressor's consciously actuated will sets his own right to life in juridic inferiority to that of the victim's right to life, and the victim may defend his own life, even unto the indirect death of the aggressor in necessity. The materially unjust aggressor attacks the victim's life unjustly, but whether the aggressor is sane or insane, the attack is not voluntary. When an insane aggressor appears to use his will, such use lacks all moral quality because of the absence of intellect and reason; he wills improperly, as a brute is said to will. In either case, nevertheless, there is active aggression directed against the victim's life, which also sets the aggressor in juridic inferiority to the victim, and permits the victim to defend his own life to extremes. As great an authority as De Lugo holds that in such defence, whether the aggressor is formally or only materially such, the victim may directly kill, but direct killing is never necessary, as it is all a matter of intention. The ectopic fetus cannot, of course, be a formal aggressor because it cannot exercise either intelligence or will. It is not a materially unjust aggressor, because the only action it is capable of is to increase in size in obedience to the natural law of growth. It is not trying in any manner to tear the maternal blood-vessels. It has a right to its own life and a right to grow. Its growth may finally bring about a maternal hemorrhage, but just now it is not causing that hemorrhage. An aggressor is such only while there is an actual attack going on here and now, directed against the victim's life. The fetus is necessarily passive always, never aggressive in any sense of the term, until the actual rupture occurs. If it may be deemed materially aggressive when the actual rupture is taking place, the question becomes irrelevant, because at that time the fetus may be removed for other reasons altogether. If an insane man is in a room with a loaded revolver which he may not use against me, but which he probably will, I may not kill him in self-defence until he actually begins the aggression. The opinion expressed here is the contrary of the opinion I expressed, in 1906, in _Essays in Pastoral Medicine_.