It's "Law of Excluded Middle". Worked great in Aristotle's Time.
   They modified it slightly in the 19th century. Boole made great
   use of it and computers, which are reaching the pinnacle of
   flip/flop form are starting to reach the limits of binary.

   But:

   In terms of human questions? They're of limited value.

   Either they exist or they don't? There's no reason why it is
   Either/Or, unless your Logic system is strictly binary in
   nature. There's more than one system of logic.