必要は英語で
necessary

英語の定義

necessary
1. adj. Required, essential, whether logically inescapable or needed in order to achieve a desired result or avoid some penalty.
Although I wished to think that all was false, it was yet necessary that that I, who thus thought, must in some sense exist.
It is absolutely necessary that you call and confirm your appointment.
2. adj. Unavoidable, inevitable.
If it is absolutely necessary to use public computers, you should plan ahead and forward your e-mail to a temporary, disposable account.
3. adj. (obsolete) Determined, involuntary: acting from compulsion rather than free will.
4. n. (archaic euphemism) A place to do the "necessary" business of urination and defecation: an outhouse or lavatory.

need
1. n. A requirement for something; something needed.
There's no need to speculate; we can easily find out for sure.
She grew irritated with his constant need for attention.
Our needs are not being met.
I've always tried to have few needs beyond food, clothing and shelter.
2. n. Lack of means of subsistence; poverty; indigence; destitution.
3. v. To have an absolute requirement for.
Living things need water to survive.
4. v. To want strongly; to feel that one must have something.
After ten days of hiking, I needed a shower and a shave.
5. v. (modal verb) To be obliged or required (to do something).
You need not go if you don't want to.
6. v. (intransitive) To be required; to be necessary.
7. v. (obsolete, transitive) To be necessary (to someone).

necessity
1. n. The quality or state of being necessary, unavoidable, or absolutely requisite.
I bought a new table out of necessity. My old one was ruined.
2. n. The condition of being needy; desperate need; lack
3. n. Something necessary; a requisite; something indispensable.
A tent is a necessity if you plan on camping.
4. n. Something which makes an act or an event unavoidable; an irresistible force; overruling power
5. n. The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism.
6. n. (legal) Greater utilitarian good; used in justification of a criminal act.
doctrine of necessity
7. n. (legal, in the plural) Indispensable requirements (of life).