Full Idea
One can observe a system and focus attention on the relations among the objects - ignoring those features of the objects not relevant to the system. For example, we can understand a baseball defense system by going to several games.
Gist of Idea
We can focus on relations between objects (like baseballers), ignoring their other features
Source
Stewart Shapiro (Philosophy of Mathematics [1997], p.74), quoted by Charles Chihara - A Structural Account of Mathematics
Book Reference
Chihara,Charles: 'A Structural Account of Mathematics' [OUP 2004], p.79
A Reaction
This is Shapiro perpetrating precisely the wicked abstractionism which Frege and Geach claim is ridiculous. Frege objects that abstract concepts then become private, but baseball defences are discussed in national newspapers.