Full Idea
The vocabulary of geometry is sufficient to identify the circle, but could not be used to identify any circular paint patch. The reason must be that the circle lacks certain properties that can distinguish paint patches from one another.
Gist of Idea
Geometrical circles cannot identify a circular paint patch, presumably because they lack something
Source
Zoltán Gendler Szabó (Nominalism [2003], 2.2)
Book Reference
'The Oxford Handbook of Metaphysics', ed/tr. Loux,M /Zimmerman,D [OUP 2005], p.17
A Reaction
I take this to be support for the traditional view, that abstractions are created by omitting some of the properties of physical objects. I take them to be fictional creations, reified by language, and not actual hidden entities that have been observed.