Full Idea
Supervaluation preserves classical logic (even though supervaluations are three-valued), except when we add the Δ operator (meaning 'definitely' or 'determinately').
Clarification
See Idea 13694 for supervaluation
Gist of Idea
Supervaluational logic is classical, except when it adds the 'Definitely' operator
Source
Theodore Sider (Logic for Philosophy [2010], 3.4.5)
Book Reference
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.85
Related Idea
Idea 13694 We can 'sharpen' vague terms, and then define truth as true-on-all-sharpenings [Sider]