Full Idea
One approach to predications in borderline cases is to say that they have a third truth value - 'neutral', 'indeterminate' or 'indefinite', leading to a three-valued logic. Or a degree theory, such as fuzzy logic, with infinite values between 0 and 1.
Gist of Idea
A third truth-value at borderlines might be 'indeterminate', or a value somewhere between 0 and 1
Source
R Keefe / P Smith (Intro: Theories of Vagueness [1997], §1)
Book Reference
'Vagueness: a Reader', ed/tr. Keefe,R /Smith,P [MIT 1999], p.7
A Reaction
This looks more like a strategy for computer programmers than for metaphysicians, as it doesn't seem to solve the difficulty of things to which no one can quite assign any value at all. Sometimes you can't be sure if an entity is vague.