Bivalence
Bivalence is the principle that every (declarative, truth-apt) sentence has exactly one of two truth values: true or false.
Why assume only two values?
It’s the foundational assumption that lets classical Sentential Logic and Propositional Logic use truth tables and binary connectives without gaps.
Non-classical pushback
Some logics drop bivalence:
- Three-valued logics add a third value (e.g., “undefined,” “neither”)
- Fuzzy logic allows degrees of truth between 0 and 1
- Intuitionistic logic rejects the law of excluded middle (P ∨ ¬P)
For everyday critical-thinking purposes, classical bivalence is assumed.