necessity defence

In the criminal law of many nations, 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. As a matter of political expediency, states usually allow some classes of person to be excused from liability when they are engaged in socially useful functions but intentionally cause injury, loss or damage.

For example, drunk drivers might contend that they drove their car to get away from being kidnapped (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 they sought to avoid outweighs the danger of the prohibited conduct they are charged with; (b) they had no reasonable alternative; (c) they ceased to engage in the prohibited conduct as soon as the danger passed; and (d) they themselves did not create the danger they 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 them.