Full Idea
What's true of the many is not exactly what's true of the one. After all they are many while it is one. The number of the many is six, whereas the number of the fusion is one.
Gist of Idea
The one has different truths from the many; it is one rather than many, one rather than six
Source
David Lewis (Parts of Classes [1991], 3.6)
Book Reference
Lewis,David: 'Parts of Classes' [Blackwell 1991], p.87
A Reaction
Together with Idea 15521, this nicely illustrates the gulf between commitment to ontology and commitment to truths. The truths about a fusion change, while its ontology remains the same. Possibly this is the key to all of metaphysics.
Related Idea
Idea 15521 Given cats, a fusion of cats adds nothing further to reality [Lewis]