- (philosophy, metaphysics, theology) Necessarianism, especially as espoused by Joseph Priestley.
- (law) A principle whereby a normally criminal act is justified by the necessity of preserving something of greater utilitarian value than that lost or sacrificed; not to be confused with self-defence.
- (politics, law) The principle that, in a situation of emergency or exigent circumstance, a state may legitimately act in ways that would normally be illegal.
- (politics, law) The principle that the laws of an illegal government should be deemed valid insofar as they do not contradict the constitution, justified on the basis that maintenance of government is of greater utilitarian value than maintenance of the law.
- (politics, international law) The principle that a state in immediate peril to its existence, from a situation not of its own doing, may in extremis be justified in violating a right of another state.