Full Idea
The usefulness of talk about possible worlds is not for purposes of individuating the object - that can be done in this world; such talk is a way of sorting its properties.
Gist of Idea
The use of possible worlds is to sort properties (not to individuate objects)
Source
Ruth Barcan Marcus (Essential Attribution [1971], p.192)
Book Reference
-: 'Nous' [-], p.192
A Reaction
'Possible worlds are a device for sorting properties' sounds to me like a promising slogan. Ruth Marcus originated rigid designation, before Kripke came up with the label.