Full Idea
One requirement for a successful count is that double counting should be avoided: a single object should not be counted twice. ...but that is to make a knowledgeable judgement of distinctness - to resolve a question of identity in the negative.
Gist of Idea
A single object must not be counted twice, which needs knowledge of distinctness (negative identity)
Source
Ian Rumfitt (Concepts and Counting [2002], III)
Book Reference
-: 'Aristotelian Society' [], p.56
A Reaction
He also notes later (p.65) that you must count all and only the right things.