Full Idea
In modern times, it was G.F. Stout who first explicitly made the proposal that properties and relations are as particular as the substances that they qualify.
Gist of Idea
Stout first explicitly proposed that properties and relations are particulars
Source
report of G.F. Stout (The Nature of Universals and Propositions [1923]) by Keith Campbell - The Metaphysic of Abstract Particulars §1
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.125
A Reaction
Note that relations will have to be tropes, as well as properties. Williams wants tropes to be parts of objects, but that will be tricky with relations. If you place two objects on a table, how does the 'to the left of' trope come into existence?