Full Idea
To me it is mysterious how a state of affairs is made out of its particular and universal constituents. Different states of affairs may have the very same constituents, and the existence of constituents by no means entails the existence of the states.
Gist of Idea
How do things combine to make states of affairs? Constituents can repeat, and fail to combine
Source
David Lewis (Armstrong on combinatorial possibility [1992], 'What is there')
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.200
A Reaction
He is rejecting the structure of states of affairs as wholes made of parts. But then mereology was never going to explain the structure of the world.