Editing Principle (section)

===Principle of excluded middle===
{{Main|Law of excluded middle}}
The principle of the excluding third or "principium tertium exclusum" is a principle of the traditional logic formulated canonically by [[Gottfried Wilhelm Leibniz|Leibniz]] as: either ''A'' is ''B'' or ''A'' isn't ''B''. It is read the following way: either ''P'' is true, or its denial ¬''P'' is.<ref>{{Cite book|url=http://name.umdl.umich.edu/AAT3201.0001.001|title=Principia mathematica, by Alfred North Whitehead ... and Bertrand Russell.|last=Whitehead|first=Alfred North|date=2005}}</ref>
It is also known as "''tertium non datur''" ('A third (thing) is not'). Classically it is considered to be one of the most important fundamental principles or laws of thought (along with the principles of identity, non-contradiction and sufficient reason).
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