Full Idea
The supervaluationist view of vagueness proposes that a sentence is true iff it is true on all precisifications, false iff false on all precisifications, and neither true nor false otherwise.
Clarification
'Precisification' is an American word meaning 'making more precise'
Gist of Idea
Vague statements lack truth value if attempts to make them precise fail
Source
R Keefe / P Smith (Intro: Theories of Vagueness [1997], §3)
Book Reference
'Vagueness: a Reader', ed/tr. Keefe,R /Smith,P [MIT 1999], p.23
A Reaction
This seems to be just a footnote to the Russell/Unger view, that logic works if the proposition is precise, but otherwise it is either just the mess of ordinary life, or the predicate doesn't apply at all.