Full Idea
For Armstrong a predicate is sparse when there exists a corresponding universal; for Lewis, a predicate is sparse when there exists a corresponding natural property or relation.
Gist of Idea
Predicates can be 'sparse' if there is a universal, or if there is a natural property or relation
Source
Theodore Sider (Writing the Book of the World [2011], 06)
Book Reference
Sider,Theodore: 'Writing the Book of the World' [OUP 2011], p.85
A Reaction
I like 'sparse' properties, but have no sympathy with Armstrong, and am cautious about Lewis. I like Shoemaker's account, which makes properties even sparser. 'Abundant' so-called properties are my pet hate. They are 'predicates'!