necessity

n. essential; indispensability; obligation; need, requirement; poverty

In criminal law, necessity may be either a possible excuse 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. For example, a drunk driver might contend that he drove 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 he sought to avoid outweighs the danger of the prohibited conduct he is charged with; (b) he had no reasonable alternative; (c) he ceased to engage in the prohibited conduct as soon as the danger passed; and (d) he did not himself create the danger 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 him.
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Noun
1. the condition of being essential or indispensable
(hypernym) need, demand
(hyponym) requisiteness
(attribute) necessary
(derivation) necessitate, ask, postulate, need, require, take, involve, call for, demand
2. anything indispensable; "food and shelter are necessities of life"; "the essentials of the good life"; "allow farmers to buy their requirements under favorable conditions"; "a place where the requisites of water fuel and fodder can be obtained"
(synonym) essential, requirement, requisite, necessary
(hypernym) thing
(hyponym) desideratum
(derivation) necessitate, ask, postulate, need, require, take, involve, call for, demand

(n.)
The quality or state of being necessary, unavoidable, or absolutely requisite; inevitableness; indispensableness.
  

(n.)
The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism.
  

(n.)
The condition of being needy or necessitous; pressing need; indigence; want.
  

(n.)
That which makes an act or an event unavoidable; irresistible force; overruling power; compulsion, physical or moral; fate; fatality.
  

(n.)
That which is necessary; a necessary; a requisite; something indispensable; -- often in the plural.
  

In general, whatever makes the contrary of a thing impossible, whatever may be the cause of such impossibilities.

Whatever is done through necessity, is done without any intention, and as the act is done without will, and is compulsory, the agent is not legally responsible. Hence the maxim, necessity has no law; indeed necessity is itself a law which cannot be avoided nor infringed.

It follows, then, that the acts of a man in violation of law., or to the injury of another, may be justified by necessity, because the actor has no will to do or not to do the thing, he is a mere tool; but, it is conceived, this necessity must be absolute and irresistible, in fact, or so presumed in point of law.

The cases which are justified by necessity, may be classed as follows: For the preservation of life; as if two persons are on the same plank, and one must perish, the survivor is justified in having thrown off the other, who was thereby drowned.

Obedience by a person subject to the power of another; for example, if a wife should commit a larceny with her husband, in this case the law presumes she acted by coercion of her husband, and, being compelled, by necessity, she is justifiable.

Those cases which arise from the act of God, or inevitable accident, or from the act of man, as public enemies.

There is another species of necessity. The actor in these cases is not compelled to do the act whether he will or not, but he has no choice left but to do the act which may be injurious to another, or to lose the total use of his property. For example, when a man's lands are surrounded by those of others, so that he cannot enjoy them without trespassing on his neighbors. The way which is thus obtained, is called a way of necessity.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.