Included Middle
Theory proposing that logic has a three-part structure: asserting something, the negation of this assertion, and a third position that is neither or both.
Origin
The concept contrasts with Aristotle's law of excluded middle, stated in Metaphysics: "There cannot be an intermediate between contradictions." The law of excluded middle (LEM) asserts that every proposition must be either true or false, not both and not neither—"not neither" means at least one must be true. The principle of non-contradiction (PNC) says "not both" (at most one is true). While Aristotelian logic insists on this binary structure, some logical systems—particularly in Eastern philosophy and modern paraconsistent logics—explore "included middle" frameworks where a third position (neither, both, or intermediate) can exist between assertion and negation.