Necessary or necessity may refer to:
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 economicsLawDoctrine 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 lawOther Necessity., 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