Full Idea
We can't dispense with structural universals if we cannot be sure that there are any simples which can be involved in them.
Gist of Idea
We can't get rid of structural universals if there are no simple universals
Source
David Lewis (Against Structural Universals [1986], 'Why believe')
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.85
A Reaction
Lewis cites this as Armstrong's strongest reason for accepting structural universals (and he takes their requirement for an account of laws of nature as the weakest). I can't comprehend a world that lacks underlying simplicity.