physical [logical] necessity 物理的[逻辑的]必然,宿命
the doctrine of necessity 宿命论
the necessity of death 死的必然性
as a necessity 必然地
bow to necessity 服从命运;屈服于需要.

Necessity is the mother of invention.【谚】需要乃发明之母.
Necessity knows [has] no law.【谚】 逼于情势,法理难禁(1914年德国总理Bethmann-Hollweg在下院演讲为进兵卢森堡及比利时作辩护时用此语)
the necessity of [for] doing 做…的必要
from [out of] (sheer) necessity (完全)出于需要
in case of necessity 必要时
under the necessity of doing 被迫做…,不得已而做…
work of necessity (在安息日允许做的)必要的工作.

Air [Water] is a necessity. 空气[水]是不可缺乏之物.
the necessities of life 生活必需品
daily necessities 日用必需品.

He is in great necessity. 他一贫如洗.