Describes something that is required or indispensable. Used as a na-adjective.
A passport is necessary for the trip.
More practice is needed.
Used as a noun to refer to the state or thing that is required.
Necessity is the mother of invention.
I explained the necessity of the plan.
To solve this problem, we need to look into it more thoroughly.
The new project will require additional staff.
I set off on the trip carrying only the bare minimum of luggage.
要る is a plain verb meaning 'to be needed' used in casual speech, while 必要 is a na-adjective/noun that sounds more formal.
必要 is the common, flexible word for 'necessary' usable as noun, adjective, or predicate, while 必需 is a stiffer, more formal term restricted to noun-modifying or compound use (as in 必需品).
必要 directly means 'necessary/needed' and modifies nouns or predicates, while 必要性 is the abstract noun form used to discuss whether or how much a need exists.
必要 refers to a personal or essential need, while 需要 refers to collective or market-level demand.
必要 is the everyday, general word for 'necessary', while 所要 is a more formal term used mainly in set phrases like 所要時間 for what is required for a specific purpose.
必要 is a native Japanese word for necessity that can be abstract or formal, while ニーズ is a loanword favored in business and marketing contexts for concrete wants or requirements.
必要 is a noun/adjective meaning 'necessary', while 要する is the verb form meaning 'to require, need' and is used in formal writing.
必要 is an abstract noun/adjective meaning 'necessary' or 'need', whereas 必需品 is the concrete physical item that fills that need.
必要 is the neutral, everyday word for 'necessary', whereas マスト is a trendy, informal loanword used mainly in fashion or lifestyle talk.
必要 simply means 'necessary/needed' and is more neutral in strength, whereas 無くてはならない emphasizes that something absolutely cannot be missing.
必要 is the plain, general word for 'necessary' applicable to anything, whereas 必携 narrows this to physical items that should be kept on hand.
必要 simply means 'necessary' or 'needed', whereas 肝要 stresses that something is critically important, not just required.
不必要 means 'unnecessary', the direct opposite of 必要 which means 'necessary'.
必要 means something is needed, the direct opposite of 無用 in its 'unnecessary' sense.
必要 means 'necessary', the direct opposite of 余計's sense of being unnecessary or uncalled-for.
必要 means 'necessary, needed', the direct opposite of 不要 'unnecessary, not needed'.
necessary and sufficient