Necessary

Necessary or necessity may refer to:

Concept of necessity

 * Need
 * An action somebody may feel they must do
 * An important task or essential thing to do at a particular time or by a particular moment
 * Necessary and sufficient condition, in logic, something that is a required condition for something else to be the case
 * Necessary proposition, in logic, a statement about facts that is either unassailably true (tautology) or obviously false (contradiction)
 * Metaphysical necessity, in philosophy, a truth which is true in all possible worlds
 * Necessity in modal logic
 * Necessity good in economics

Law

 * Doctrine of necessity, a concept in constitutional law
 * Military necessity, a concept in international law
 * Necessity (criminal law), a defence in criminal law
 * Necessity (tort), a concept in the law of tort
 * A necessity in contract law

Other uses

 * , a poem by Letitia Elizabeth Landon being part of Three Extracts from the Diary of a Week, 1837.
 * "Necessary" (song), by Every Little Thing, 1998
 * A bathroom or toilet, in some languages (in English this is an archaic usage)
 * An economic need enunciated by US President Franklin D. Roosevelt in his 1944 Second Bill of Rights
 * Necessity (novel), of 2016 by Jo Walton
 * Necessary Records, UK record label