| bivalenza | : P è o vero o falso. | wp |
| non-contraddizione | : not(P e (non-P)) è vero. | wp |
| terzo escluso | : (P o non-P) è vero. | wp |
di 2 proposizione contraddittorie,
una deve essere vera e l'altra falsa.
2 proposizioni contraddittorie una e' la negazione dell'altra
2-valued logic bivalent logic a logic satisfying the principle of bivalence.
The principle of bivalence is studied in philosophical logic to address the question of which natural-language statements have a well-defined truth value.
Sentences that predict events in the future, and sentences that seem open to interpretation, are particularly difficult for philosophers who hold that the principle of bivalence applies to all declarative natural-language statements.
Many-valued logics formalize
a realistic characterization of the notion of consequence
that requires the admissibility of premises that cannot be considered classically bivalent, owing to vagueness, temporal or quantum indeterminacy, or reference-failure.