In criminal law, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when that conduct is not excused under some other more specific provision of law such as self defense.
For example, a drunk driver might contend that s/he drove her/his car to get away from a kidnap (cf. North by Northwest). Most common law and civil law jurisdictions recognize this defense, but only under limited circumstances. Generally, the defendant must affirmatively show (i.e., introduce some evidence) that (a) the harm s/he sought to avoid outweighs the danger of the prohibited conduct s/he is charged with; (b) s/he had no reasonable alternative; (c) s/he ceased to engage in the prohibited conduct as soon as the danger passed; and (d) s/he did not her/himself create the danger s/he sought to avoid. Thus, with the "drunk driver" example cited above, the necessity defense will not be recognized if the defendant drove further than was reasonably necessary to get away from the kidnapper, or if some other reasonable alternative was available to her/him.
In one case, police decided not to prosecute someone who ran from the scene of an accident, when presented with evidence that the person did not run for the purposes of trying to evade responsibility, but ran because a mob showed up, wanting to assault and/or kill the person for having struck a pedestrian.
In English law, the defence of necessity recognises that there may be situations of such an overwhelming urgency, that a person must be allowed to respond by breaking the law. There have been very few cases in which the defence has succeeded but the Crown Prosecution Service tends to exercise a discretion not to prosecute those cases where it believes that the potential defendants have acted reasonably in all the circumstances.
a liberal and humane criminal law cannot hold people to the strict obedience of laws in emergency situations where normal human instincts, whether of self-preservation or of altruism, overwhelmingly impel disobedience.However, it must be "strictly controlled and scrupulously limited." and can only be applied in the strictest of situations where true "involuntariness" is found. Three elements are required for a successful defence :
Each element must be proven on an objective standard. The peril or danger must be more than just foreseeable or likely. It must be near and unavoidable.
At a minimum the situation must be so emergent and the peril must be so pressing that normal human instincts cry out for action and make a counsel of patience unreasonable.With regard to the second element, if there was a realistic or objectively reasonable legal alternative to breaking the law, then there can be no finding of necessity. Regarding the third element requiring proportionality, the harm avoided must be at least comparable to the harm inflicted.
In R. v. Latimer (2001), the Supreme Court of Canada affirmed that the defense of necessity is not available to a defendant when (1)the killing occurred when there was no imminent danger to either the defendant or the victim, (2) reasonable legal alternatives are available besides killing, and (3) the harm inflicted is not in proportion to the harm avoided.
§ 3.02 (1) Conduct which the actor believes to be necessary to avoid a harm or evil to himself or another is justifiable . . . .
The use of the defense is subject to certain limitations, notably: that the harm to be prevented be greater than that caused (§ 3.02(1)(a)); that it not be excluded by the law (§ 3.02(1)(b)) or a plain legislative purpose (§ 3.02(1)(c)); and that the actor not have recklessly or negligently have created the emergency, where the crime charged requires recklessness or negligence (§ 3.02(2)).
Note that the Model Penal Code is not the law of any state, though many states have adopted some of its rationale or provisions.
§ 35.05 Justification; generally.Unless otherwise limited by the ensuing provisions of this article defining justifiable use of physical force, conduct which would otherwise constitute an offense is justifiable and not criminal when:1. Such conduct is required or authorized by law or by a judicial decree, or is performed by a public servant in the reasonable exercise of his official powers, duties or functions; or2. Such conduct is necessary as an emergency measure to avoid an imminent public or private injury which is about to occur by reason of a situation occasioned or developed through no fault of the actor, and which is of such gravity that, according to ordinary standards of intelligence and morality, the desirability and urgency of avoiding such injury clearly outweigh the desirability of avoiding the injury sought to be prevented by the statute defining the offense in issue. The necessity and justifiability of such conduct may not rest upon considerations pertaining only to the morality and advisability of the statute, either in its general application or with respect to its application to a particular class of cases arising thereunder. Whenever evidence relating to the defense of justification under this subdivision is offered by the defendant, the court shall rule as a matter of law whether the claimed facts and circumstances would, if established, constitute a defense.
Under the "choice-of-evils" theory of section 35.05, it is a question of fact for the criminal jury whether the conduct was justified under the circumstances. See People of the State of New York v. Maher, 79 N.Y.2d 978 (1992) As discussed in People of the State of New York v. Gray, 150 Misc. 2d 852 (N.Y. Co. 1991),the defendant is generally held to a "reasonableness" standard--the question is whether a reasonable person in the defendant's position would have reached the conclusion that the relevant conduct was necessary. It is not necessary that the defendant actually avert a greater harm, just that his or her belief be reasonable. As the court observed:
To apply a strict liability standard in evaluating the other elements of this defense, however, and to find that only those actors who have actually averted a greater harm may avail themselves of the defense, is inconsistent with the law of justification in New York, as well as necessity's basic purpose to promote societal interests.
However, the defendant is subject to strict liability as to which harm is greater. For example, a defendant cannot choose to value property over life.
Similarly, when using physical force in defense of a person, the focus of the defense is not on whether the actor was in fact correct that his or her conduct was necessary to prevent harm, but whether that belief was reasonable. Section 35.15 (1) provides in relevant part:
1. A person may, subject to the provisions of subdivision two, use physical force upon another person when and to the extent he reasonably believes such to be necessary to defend himself or a third person from what he reasonably believes to be the use or imminent use of unlawful physical force by such other person . . . .
Thus, with respect to the example given above, the actor would, provided his or her belief was reasonable, be entitled to have a defense of justification presented to a jury.
It is important to distinguish between the defense of justification/necessity under Article 35 and the law of citizen's arrest. In general, to use physical force a private citizen must in fact be correct that a person has committed an offence, while a police officer must only have a reasonable belief.