necessary

Necessary is a word used to describe something that must be done, achieved, or obtained in order for a particular outcome to occur. In everyday use, it means essential or indispensable within a given context. The degree of necessity depends on goals, constraints, and alternatives; what is necessary in one situation may not be in another.

In grammar, necessary can appear as an adjective modifying nouns (a necessary condition, necessary tools) or in constructions with to: It is necessary to obtain a visa before travel. It is also used with for: A visa is necessary for travel. The word is often contrasted with optional and with unnecessary, the latter indicating not required.

In logic and philosophy, a necessary condition for a proposition is something that must hold if the proposition is true, but does not by itself guarantee truth. For example, having oxygen is a necessary condition for human life, but not sufficient by itself.

Etymology: Necessary comes from Latin necessarius, from necessitas “necessity,” through Old French necessaire into Middle English. Related forms include necessity (noun) and necessarily (adverb). In modern usage, the plural noun necessaries is uncommon and is usually replaced by necessities or basic needs.

Examples: It is necessary to wear a seatbelt while driving. Clean water is a basic necessity. Some costs are seen as a necessary evil when a project delivers greater benefits despite drawbacks.