§ 139 Jus Necessitatis
We shall conclude our examination of the theory of wilful wrongdoing by considering a special case in which, although intention is present, the mens rea is nevertheless absent. This is the case of the jus necessitatis. So far as the abstract theory of responsibility is concerned, an act which is necessary is not wrongful, even though done with full and deliberate intention. It is a familiar proverb that necessity knows no law: Necessitas non habet legem. By necessity is here meant the presence of some motive adverse to the law, and of such exceeding strength as to overcome any fear that can be inspired by the threat of legal penalties. The jus necessitatis is the right of a man to do that from which he cannot be dissuaded by any terror of legal punishment. Where threats are necessarily ineffective, they should not be made, and their fulfilment is the infliction of needless and uncompensated evil.
The common illustration of this right of necessity is the case of two drowning men clinging to a plank that will not support more than one of them. It may be the moral duty of him who has no one dependent on him to sacrifice himself for the other who is a husband or a father; it may be the moral duty of the old to give way to the young. But it is idle for the law to lay down any other rule save this, that it is the right of the stronger to use his strength for his own preservation. Another familiar case of necessity is that in which shipwrecked sailors are driven to choose between death by starvation on the one side and murder and cannibalism on the other. A third case is that of crime committed under the pressure of illegal threats of death or grievous bodily harm. “If,” says Hobbes,356 “a man by the terror of present death be compelled to do a fact against the law, he is totally excused; because no law can oblige a man to abandon his own preservation.”
It is to be noticed that the test of necessity is not the powerlessness of any possible, but that of any reasonable punishment. It is enough if the lawless motives to an act will necessarily countervail the fear of any penalty which it is just and expedient that the law should threaten. If burning alive were a fit and proper punishment for petty theft, the fear of it would probably prevent a starving wretch from stealing a crust of bread; and the jus necessitatis would have no place. But we cannot place the rights of property at so high a level. There are cases, therefore, in which the motives to crime cannot be controlled by any reasonable punishment. In such cases an essential element of the mens rea, namely freedom of choice, is absent; and so far as abstract theory is concerned, there is no sufficient basis of legal liability.
As a matter of practice, however, evidential difficulties prevent any but the most limited scope being permitted to the jus necessitatis. In how few cases can we say with any approach to certainty that the possibility of self-control is really absent, that there is no true choice between good and evil, and that the deed is one for which the doer is rightly irresponsible. In this conflict between the requirements of theory and the difficulties of practice the law has resorted to compromise. While in some few instances necessity is admitted as a ground of excuse, it is in most cases regarded as relevant to the measure rather than to the existence of liability. It is acknowledged as a reason for the reduction of the penalty, even to a nominal amount, but not for its total remission. Homicide in the blind fury of irresistible passion is not innocent, but neither is it murder; it is reduced to the lower level of manslaughter. Shipwrecked sailors who kill and eat their comrades to save their own lives are in law guilty of murder itself; but the clemency of the Crown will commute the capital sentence to a short term of imprisonment.357