|Law of the Excluded Middle: an assertion is either true or false. "There is no third possibility."See also bivalence, anti-realism, multivalued logic.|
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|Excluded Middle||Berka I 170
SaD/Modal Logic/Becker/Berka: there is a triple SaD here: 1) p is either true or false (untrue - 2) p is either necessary or possibly false (not necessary) - 3) p is either possible (not impossible ) or impossible - but it obviously does not apply: - "p is either necessary (tautological) or impossible (contradictory)" - i.e. the SaD does not apply in the "logic of the necessities", but the principle of contradiction does apply - no statement both necessary and impossible at the same time - against: logic of possibilities: here precisely the SaD applies: - "a statement is always possibly true or possibly false" - but not the SvW: a statement cannot be possibly true and possibly false at the same time" - I 171 so we have: "p is either necessary or impossible, or at the same time possibly true and possibly false (i.e. "undefined" or "neither necessary nor impossible").
K. Berka/L. Kreiser
Logik Texte Berlin 1983