Full Idea
It is hard to see classes as an 'addition of being'; God does not create the world, and then add the classes.
Gist of Idea
God does not create the world, and then add the classes
Source
John Heil (From an Ontological Point of View [2003], 13.4 n6)
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.143
A Reaction
This seems right. We may be tempted into believing in the reality of classes when considering maths, but it seems utterly implausible when considering trees or cows.