of necessity
  必然地,不可避免地,不得已地
  Ne·ces·si·ty n.; pl. Necessities
  1. The quality or state of being necessary, unavoidable, or absolutely requisite; inevitableness; indispensableness.
  2. The condition of being needy or necessitous; pressing need; indigence; want.
     Urge the necessity and state of times.   --Shak.
     The extreme poverty and necessity his majesty was in.   --Clarendon.
  3. That which is necessary; a necessary; a requisite; something indispensable; -- often in the plural.
  These should be hours for necessities,
  Not for delights.   --Shak.
  What was once to me
  Mere matter of the fancy, now has grown
  The vast necessity of heart and life.   --Tennyson.
  4. That which makes an act or an event unavoidable; irresistible force; overruling power; compulsion, physical or moral; fate; fatality.
  So spake the fiend, and with necessity,
  The tyrant's plea, excused his devilish deeds.   --Milton.
  5. Metaph. The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism.
  Of necessity, by necessary consequence; by compulsion, or irresistible power; perforce.
  Syn: -- See Need.
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  of necessity
       adv : in such a manner as could not be otherwise; "it is
             necessarily so"; "we must needs by objective" [syn: inevitably,
              necessarily, needs]