Full Idea
The term 'abstract entities' may not be entirely clear, but one thing that does seem clear is that such alleged entities as numbers, functions and sets are abstract.
Gist of Idea
'Abstract' is unclear, but numbers, functions and sets are clearly abstract
Source
Hartry Field (Science without Numbers [1980], p.1), quoted by JP Burgess / G Rosen - A Subject with No Object I.A.1.a
Book Reference
Burgess,J/Rosen,G: 'A Subject with No Object' [OUP 1997], p.13
A Reaction
Field firmly denies the existence of such things. Sets don't seem a great problem, if the set is a herd of elephants, but the null and singleton sets show up the difficulties.