Full Idea
One version of realism says that the universal does not enter into the being of its instances, and thus is a One-Over-Many. One version of this is the model/copy view, but this is not widely held, because of difficulties such as the Third Man Argument.
Clarification
The 'Third Man' involves using a model to identify the model, which gives an infinite regress
Gist of Idea
One realism is one-over-many, which may be the model/copy view, which has the Third Man problem
Source
J.P. Moreland (Universals [2001], Ch.1)
Book Reference
Moreland,J.P.: 'Universals' [Acumen 2001], p.7
A Reaction
This presumably arises if the model is held to have the properties of the copy (self-predication), and looks like a bad theory