Synonyms:
| essential, | infallible, | required, | unavoidable, |
| indispensable, | needed, | requisite, | undeniable. |
| inevitable, | needful, | ||
That is necessary which must exist, occur, or be true; which in the nature of things can not be otherwise. That which is essential belongs to the essence of a thing, so that the thing can not exist in its completeness without it; that which is indispensable may be only an adjunct, but it is one that can not be spared; vigorous health is essential to an arctic explorer; warm clothing is indispensable. That which is requisite (or required) is so in the judgment of the person requiring it, but may not be so absolutely; thus, the requisite is more a matter of personal feeling than the indispensable. Inevitable (L. in, not, and evito, shun) is primarily the exact equivalent of the Saxon unavoidable; both words are applied to things which some at least would escape or prevent, while that which is necessary may meet with no objection; food is necessary, death is inevitable; a necessary conclusion satisfies a thinker; an inevitable conclusion silences opposition. An infallible proof is one that necessarily leads the mind to a sound conclusion. Needed and needful are more concrete than necessary, and respect an end to be attained; we speak of a necessary inference; necessary food is what one can not live without, while needful food is that without which he can not enjoy comfort, health, and strength.
Antonyms:
| casual, | needless, | optional, | useless, |
| contingent, | non-essential, | unnecessary, | worthless. |
Prepositions:
Necessary to a sequence or a total; for or to a result or a person; unity is necessary to (to constitute) completeness; decision is necessary for command, or for a commander.