bivalence
In logic, the semantic principle (or law) of bivalence states that every declarative sentence expressing a proposition (of a theory under inspection) has exactly one truth value, either true or false.[1][2] A logic satisfying this principle is called a two-valued logic[3] or bivalent logic.[2][4]
In formal logic, the principle of bivalence becomes a property that a
semantics may or may not possess. It is not the same as the law of excluded middle, however, and a semantics may satisfy that law without being bivalent.[2] It may be written in the second-order sentence as: 
, demonstrating similarity yet differing mainly by quantified set elements.
