An Etymological Dictionary of Astronomy and Astrophysics

The second principle of → formal logic introduced in Aristotle’s theory of the → syllogism: A
statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.

See also: → principle; → exclude; → middle.