Full Idea
Given a prior commitment to cats, a commitment to cat-fusions is not a further commitment. The fusion is nothing over and above the cats that compose it. It just is them. They just are it.
Gist of Idea
A commitment to cat-fusions is not a further commitment; it is them and they are it
Source
David Lewis (Parts of Classes [1991], p.81), quoted by Achille Varzi - Mereology 4.3
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.17
A Reaction
I take this to make Lewis a nominalist, saying the same thing that Goodman said about Utah in Idea 10657. Any commitment to cat-fusions being more than the cats, or Utah being more than its counties, strikes me as crazy.
Related Idea
Idea 10657 The counties of Utah, and the state, and its acres, are in no way different [Goodman]