It is a question of fact in each case whether the harm to be prevented or avoided was of such a nature and so imminent as to justify or excuse the risk of doing the act with the knowledge that it was likely to cause harm.
Section 81 excuses the doing of an evil so that good may result. It permits the infliction of a lesser evil in order to prevent greater evil. According to Mayne, Section 81 is intended to give legislative sanction to the principle that where, on a sudden and extreme emergency, one or other of the two evils is inevitable, it is lawful so to direct events that the smaller only shall occur. But no amount of necessity will justify a man to steal clothes or food howsoever dire the necessity may be.
A, a captain of a steam vessel, suddenly and without any fault or negligence on his part, finds himself in such a position that, before he can stop his vessel, he must inevitably run down a boat B, with 20 or 30 passengers on board, unless he changes the course of his vessel, and that by changing his course, he must incur risk of running down a boat C with only two passengers on board, which he may possibly clear.
Here, if A alters his course without any intention to run down the boat C and in good faith for the purpose of avoiding the danger to the passengers in the boat B, he is not guilty of an offence, though he may run down the boat C by doing an act which he knew was likely to cause that effect, if it be found as a matter of fact that the danger which he intended to avoid was such as to excuse him in incurring the risk of running down C.
A, in a great fire, pulls down houses in order to prevent the conflagration from spreading. He does this with the intention in good faith of saving human life or property. Here if it be found that the harm to be prevented was of such a nature and so imminent as to excuse A’s act, A is not guilty of the offence.
These considerations apply to the case of a chance of evils. Suppose, in delivering a woman it is necessary to sacrifice the child’s life to save the mother, it is no offence. It is also a defence in those cases where the question is not which one shall live but whether any shall live; as where three mountaineers are roped together but two of them slip and the third cuts the rope to save himself from being dragged to death with them. In such a case the defence should be that there was no actus reus for the survivor had not caused the death of the other but had merely severed the rope to prevent them from pulling him down also.
Section 81 comes into play when the person confining has a genuine and reasonable apprehension that to allow the other to remain at large will endanger the person and property of others. So in order to attract Section 81 it should be shown that the act complained of was done in good faith in order to prevent or avoid harm to the person or property of others. Where a person is subjected to humiliation and disgrace with his consent in order to avoid dire consequences resulting from his own indecent behaviour, the application of Section 81 will be attracted.
If a prisoner escapes from a jail to avoid being burnt to death by fire caused by bombing, he is not guilty of escaping from lawful custody. He does not act with any criminal intention. He acts in good faith to prevent the loss of his life. It would indeed be foolish to punish him under such circumstances.
The killing of another for eating flesh to save oneself from death by starvation is not excused because such death being a slow process cannot be said to be imminent, besides it is done with a criminal intention. Good faith and absence of criminal intention are essential before any act in such circumstances may be excused.
The general principle of criminal law is that the physical act must be contemporaneous with the guilty mind. Where the guilty mind is missing, the act, however harmful, shall cease to be an offence. The principle has been expressed in the well-known Latin maxim “actus non facit reum, nisi mens sit rea” which means that the intent and act must both concur to constitute the crime.
For brevity the principle is frequently referred to as the principle of mens rea. A man cannot intentionally commit a crime in order to avoid other greater harm and if he does so he is guilty of an offence irrespective of the harm which he seeks to prevent.
The case of the captain of a ship who has no course left open to him except either to suffer death of the crew of his own ship by damage at sea or cause destruction of any of the two other boats carrying lesser number of passengers is different.
It is not for him to make a choice whether he should drown the boats. The destruction of any one of the boats including his own ship being inevitable and imminent, he prefers the lesser harm to a greater harm and he does so with due care and attention, in other words, in good faith and not from an evil bias. If the mind of the person doing an act is innocent, such act ceases to be an offence, in other words, the author of such act is not liable to punishment.