excluded middle

Exclude \Ex*clude"\, v. t. [imp. & p. p. {Excluded}; p. pr. &
   vb. n. {Excluding}.] [L. excludere, exclusum; ex out +
   claudere to shut. See {Close}.]
   1. To shut out; to hinder from entrance or admission; to
      debar from participation or enjoyment; to deprive of; to
      except; -- the opposite to admit; as, to exclude a crowd
      from a room or house; to exclude the light; to exclude one
      nation from the ports of another; to exclude a taxpayer
      from the privilege of voting.
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            And none but such, from mercy I exclude. --Milton.
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   2. To thrust out or eject; to expel; as, to exclude young
      animals from the womb or from eggs.
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   {Excluded middle}. (logic) The name given to the third of the
      "three logical axioms," so-called, namely, to that one
      which is expressed by the formula: "Everything is either A
      or Not-A." no third state or condition being involved or
      allowed. See {Principle of contradiction}, under
      {Contradiction}.
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