词典释义：
[mass noun]the fact of being necessary
必要（性）。
(
需要；必要；不可或缺
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the necessity for law and order .法律和秩序的必要性。
unavoidability
必然性
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the necessity of growing old .衰老的必然性。
a state of things or circumstances enforcing a certain course
强制性，强迫性
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created more by necessity than design .多因不得已而创作，而非计划如此。
an indispensable thing
必需品
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a good book is a necessity when travelling .出门旅行时，一本好书是必不可少的。
[mass noun]
【哲】 必然性。
[count noun]a condition that cannot be otherwise, or a statement asserting this
必然情况；断言。
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necessity is the mother of invention proverb when the need for something becomes imperative, you are forced to find ways of getting or achieving it. 〈谚〉 需要乃发明之母 -
of necessity unavoidably 势必，必定，不可避免地
"late Middle English; from Old French
