The two grounds of justification known as necessity and private defence are closely related. In both cases the perpetrator protects interests which are of value to her, such as life, physical integrity and property, against threatening danger. The distinctions between these two grounds of justification are the following (Snyman C.R: 2008):
(1) the origin of the situation of emergency: Private defence always stems from an unlawful (and therefore human) attack; necessity, on the other hand, may stem either from an unlawful human act, or from chance circumstances, such as natural occurrences.
(2) the object at which the act of defence is directed: Private defence is always directed at an unlawful human attack; necessity is directed at either the interests of another innocent third party or merely amounts to a violation of a legal provisio:
E.G: X, who has a gun, tells Y that he kidnapped Y’s daughter and orders Y, the bank manager, to use his code to open the safe of the bank and to hand him all the money inside the safe. If Y does not do what he says he, X will kill his daughter. If Y hands him the money he will be harming the bank and therefore act in necessity. If he takes his own gun and shoot X because he knows that X lied and that his daughter is safe, he will be acting in private defence to protect this own and the interest of the bank.
The distinction between necessity and private defence is also illustrated by the requirements for the successful plea of the grounds of justification (necessity and private defence). These requirements are described below:
NECESSITY A person acts out of necessity – and her conduct is therefore lawful – if she acts in the protection of her own or somebody else’s life, physical integrity, property or other legally recognised interest which is endangered by a threat of harm which has already begun or is immediately threatening and which cannot be averted in any other way; provided that the person who relies on the necessity is not legally compelled to endure the danger, and the interest protected by the act of defence is not out of proportion to the interest threatened by such an act (Burchell, J:2004). This defence arises when a person is confronted with a choice between suffering an injustice and breaking the law. It is regularly used to justify actions in emergencies. One would, for instance, be able to rely on necessity against a charge of speeding when driving a person requiring urgent medical care to hospital.
Requirements of Necessity (1) Some legal interest of X, such as her life, physical integrity or property must be threatened. In principle, one should also be able to protect other interests such as dignity, freedom and chastity in a situation of necessity.
(2) One can also act in a situation of necessity to protect another’s interest, for example where X protects Z from being attacked by an animal.
(3) The emergency must already have begun or be imminent, but must not have terminated, nor be expected in the future only.
(4) Whether a person can rely on the defence of necessity if she herself is responsible for the emergency, is a debatable question. In our opinion X should not be precluded from successfully raising this defence merely because she caused the emergency herself. If she were precluded, this would mean that if, because of X’s carelessness, her baby swallowed an overdose of pills, X would not be allowed to exceed the speed limit while rushing the baby to hospital, but would have to resign herself to the child’s dying (compare the facts in Pretorius supra). The two acts, namely the creation of danger and rescue from it, should be separated. If the first act amounts to a crime X can be punished for it, for example where she sets fire to a house and then has to break out of the house to save her own life (Milton, J.R.L:1997).
(5) If somebody is legally compelled to endure the danger, she cannot rely on necessity. Persons such as policemen, soldiers and firemen cannot avert the dangers inherent in the exercise of their profession by infringing the rights of innocent parties. Another aspect of this rule is that a person cannot rely on necessity as a defence if what appears to her to be a threat is in fact lawful (human) conduct. Thus it was held in Kibi 1978 (4) SA 173 (EC) that if X is arrested lawfully, he may not damage the police van in which he has been locked up, in order to escape from it.
(6) The act committed in necessity is lawful only if it is the only way in which X can avert the threat or danger. Where, for example, Z orders X to kill Y and threatens to kill X if she does not obey, and it appears that X can overcome her dilemma by fleeing, she must flee, and if possible, seek police protection (Bradbury 1967 (1) SA 387 (A) 390).
(7) X must be conscious of the fact that an emergency exists, and that she is therefore acting out of necessity. There is no such thing as a chance or accidental act of necessity. If X throws a brick through the window of Y’s house in order to break in, and it later appears that by so doing she has saved Z, who was sleeping in a room filled with poisonous gas, from certain death, X cannot rely on necessity as a defence.
(8) The harm occasioned by the defensive act must not be out of proportion to the interest threatened, and therefore X must not cause more harm than is necessary to escape the danger. It is this requirement which is the most important one in practice, and it can also be the most difficult to apply. The protected and the impaired interests are often of a different nature, for example where somebody damages another’s property in protecting her own physical integrity.