Full Idea
Many decent candidates could the referent of this 'cup', differing over whether outlying particles are parts. No further sortal I could invoke will be selective enough to rule out all but one referent for it.
Gist of Idea
No sortal could ever exactly pin down which set of particles count as this 'cup'
Source
Jonathan Schaffer (Deflationary Metaontology of Thomasson [2009], 3.1 n8)
Book Reference
-: 'Philosophical Books' [-], p.148
A Reaction
I never had much faith in sortals for establishing individual identity, so this point comes as no surprise. The implication is strongly realist - that the cup has an identity which is permanently beyond our capacity to specify it.