Full Idea
If one is very close to a conceptual boundary, then one's judgement will be too unreliable to constitute knowledge, and therefore one will be ignorant.
Gist of Idea
Close to conceptual boundaries judgement is too unreliable to give knowledge
Source
Timothy Williamson (Interview with Baggini and Stangroom [2001], p.156)
Book Reference
Baggini,J/Stangroom,J: 'New British Philosophy' [Routledge 2002], p.156
A Reaction
This is the epistemological rather than ontological interpretation of vagueness. It sounds very persuasive, but I am reluctant to accept that reality is full of very precise boundaries which we cannot quite discriminate.