Full Idea
Nominalists must at heart be materialists, or so it seems to me: otherwise their scruples are unintelligible.
Gist of Idea
Nominalism only makes sense if it is materialist
Source
Hilary Putnam (Philosophy of Logic [1971], Ch.5)
Book Reference
Putnam,Hilary: 'Philosophy of Logic' [Routledge 1972], p.36
A Reaction
This is modern nominalism - the rejection of abstract objects. I largely plead guilty to both charges.