Full Idea
It is sometimes argued that if there is such a thing as a mountain it would be a vague object, but it is logically impossible for an object to be vague, so there is no such thing as a mountain.
Gist of Idea
There cannot be vague objects, so there may be no such thing as a mountain
Source
Timothy Williamson (The Philosophy of Philosophy [2007], 7.2)
Book Reference
Williamson,Timothy: 'The Philosophy of Philosophy' [Blackwell 2007], p.218
A Reaction
I don't take this to be a daft view. No one is denying the existence of the solid rock that is involved, but allowing such a vague object may be a slippery slope to the acceptance of almost anything as an 'object'.