Full Idea
Where my cat (Bruce) ends, there the density of matter, the relative abundance of chemical elements, abruptly change. Bruce is also a locus of causal chains, which traces back to natural properties. Natural properties belong to well demarcated things.
Gist of Idea
Objects are demarcated by density and chemistry, and natural properties belong in what is well demarcated
Source
David Lewis (New work for a theory of universals [1983], 'Cont of L')
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.220
A Reaction
This is an amazingly convoluted way to define natural properties in terms of the classes they generate, but it seems obvious to me that the properties are logically prior to the classes.