Full Idea
Vague words have hidden boundaries. The subtraction of a single grain of sand might turn a heap into a non-heap.
Gist of Idea
Vague words have hidden boundaries
Source
Roy Sorensen (Vagueness and Contradiction [2001], Intro)
Book Reference
Sorensen,Roy: 'Vagueness and Contradiction' [OUP 2004], p.1
A Reaction
The first sentence could be the slogan for the epistemic view of vagueness. The opposite view is Sainsbury's - that vague words are those which do not have any boundaries. Sorensen admits his view is highly counterintuitive. I think I prefer Sainsbury.